Patent Application
20240271037
This application claims the benefit of both priorities of Singapore Patent Application No. 10202107417Q filed on 6 Jul. 2021 and 10202201079R filed on 4 Feb. 2022, the contents of both being hereby incorporated by reference in its entirety for all purposes.
The present invention relates to a nanocrystal having a core-shell structure, wherein the core comprises a core perovskite structure, and the shell comprises a shell perovskite structure and a compound comprising silicon and oxygen, wherein the shell perovskite structure is different from the core perovskite structure and comprises a low-dimensional perovskite structure that is doped with a metal halide comprising a monovalent, divalent or trivalent metal ion. The present invention also relates to a process for preparing the nanocrystal, a substrate comprising the nanocrystal and the use of the nanocrystal.
Halide perovskite nanocrystals (HPNCs) with general formula ABX3, where A=CH3NH3+, CH(NH2)2+, Cs+, Rb+; B=Pb2+, Sn2+, Ge2+; X═I−, Br−, Cl−, F− are highly promising emergent nanomaterials with outstanding optoelectronic properties such as high carrier mobilities, long carrier diffusion lengths. defect tolerance, tunable emission wavelengths, large linear absorption and multi-photon absorption (MPA) cross-sections and near-unity photoluminescence quantum yield (PLQY). Recently, functional ion doping or substitution with halogens, transition metals (Mn and Fe) and rare earths (Er and Yb) have not only enabled low-lead or lead-free HPNCs with reduced toxicity, but have also facilitated further tailoring of their optical and electromagnetic properties for applications in sensing, spintronics, and quantum cutting, in particular in light-emitting diodes (LEDs), solar cells, photodetectors, and lasers.
Nevertheless, all HPNCs (with or without doping) suffer from an inherent major weakness of poor ambient stability such as water, oxygen, heat or irradiation. In particular, water degradation severely limits their practical applications. Even trace amounts of water (H2O) can drastically affect their performance. Most stability studies of HPNCs dispersed in water have only been performed using the green-emitting MAPbBr3 (MA=CH3NH3+) and CsPbBr3. Related studies on their chloride (blue emission) and iodide (red or infrared emission) counterparts are few and far between due to their much poorer water stability likely from their lower defect tolerance and ion migration issues. Research in functional ion-doped or substituted perovskite nanocrystals is still nascent with most studies focused mainly on basic optical characterization.
Nonetheless, the adverse effects of water on these perovskite nanocrystals are still expected to be present, as: (i) water molecules can destroy the nanocrystal structure, and/or (ii) coupling of the high-frequency stretching vibration of O—H in water molecules with most B-site doped ions, result in non-radiative decay and fluorescence quenching. Presently, it is extremely challenging to prepare colloidal HPNCs that emit across the full colour spectrum that also remain stable in water even for one day. Accordingly, existing approaches to tune the broad emission spectrum of perovskite nanocrystals relies on the use of organic halides with high solubility in organic systems, such as haloalkane solvents used with a strong nucleophile, long alkyl-based oleylammonium iodide and aryl-based aniline hydoroiodide, to alter the properties of the HPNCs.
Despite possessing the largest MPA cross-sections, the instability of the HPNCs in water has also severely curtailed the potential of colloidal HPNCs as a fluorophore for multi-photon bioimaging applications. Ultra-bright low-toxicity multicolour HPNCs with greatly enhanced water, light and chromatic stabilities will extend the boundaries of lighting, flat panel display and biological imaging technologies.
There is therefore a need for development of a nanocrystal that overcomes or at least ameliorates, one or more of the disadvantages described above.
In an aspect, there is provided a nanocrystal having a core-shell structure, wherein the core of the core-shell structure is at least partially encapsulated by the shell of the core-shell structure, wherein:
the shell of the core-shell structure comprises a shell perovskite structure and a compound comprising silicon and oxygen, wherein the shell perovskite structure is different from the core perovskite structure and comprises a low-dimensional perovskite structure that is doped with a metal halide comprising a monovalent, divalent or trivalent metal ion.
Advantageously, the nanocrystal as defined above may have high brightness and may emit across the full colour spectrum depending on the metal halide used to dope the low-dimensional perovskite structure.
The nanocrystal may advantageously have high dispersibility in water and may possess excellent water stability. Such stability and dispersibility may be unprecedented. For example, in water, the green and blue emitting nanocrystals may possess a photoluminescence quantum yield (PLQY) of ≥80% and ≥35%, respectively, for more than 7720 hours and 7000 hours, respectively. For the red-emitting HPNCs, the PLQY in water may reach about 30% for about 750 hours, which may be a significant improvement compared to conventional red-emitting unprotected iodide perovskite nanocrystals, whose fluorescence may rapidly quench when in contact with moisture. Further advantageously, the low-dimensional perovskite structures on the surface of the core perovskite structure may confer excellent passivation, protection, and biocompatibility to the nanocrystal in conjunction with the compound comprising silicon and oxygen, which may at least partially encapsulate the nanocrystal, thereby improving its stability.
Advantageously, the nanocrystals may possess high multiphoton action cross-sections in water that may be 4 to 5 orders of magnitude larger than that of the most advanced, specially designed organic molecules in organic solutions.
Further advantageously, the nanocrystals may have low biological toxicity.
Advantageously, the presence of the metal halide and the compound comprising silicon and oxygen may synergistically facilitate high performance, high emission across the full colour spectrum at high PLQY, as well as high stability and dispersibility in water, and low toxicity.
In another aspect, there is also provided a process of preparing the nanocrystal as defined above, comprising a step of simultaneously mixing in a mixing solvent, a core perovskite structure having a formula ABX3, a metal halide comprising a monovalent, divalent or trivalent metal ion and a precursor compound comprising silicon and oxygen, wherein:
Advantageously, the method may achieve ion doping or substitution of both the core and shell of the core-shell structure, wherein the shell comprises the shell perovskite structure and the compound comprising silicon and oxygen. The ion doping or substitution may basically occur in the perovskite structure. The synergistic implementation of these two processes may circumvent introduction of unnecessary surface defects on the nanocrystals, which may be common in typical multi-step syntheses. This may result in better surface passivation of the nanocrystals, thus ensuring that the nanocrystals may maintain high performance while improving water stability.
The method may further advantageously be performed at low temperatures and may be a simple chemical synthesis under atmospheric conditions, which may facilitate large scale, cost-efficient and time-efficient preparation of the nanocrystals. This may be contrary to conventional perovskite nanocrystal synthesis, which may require high temperature or inert atmosphere preparation. Further advantageously, the method may not only be highly versatile and cost-effective, but may also result in the formation of perovskite nanocrystals that may emit across the full colour spectrum.
In an example, prior to the mixing step, the process may further comprise the step of dissolving the metal halide in a polar solvent comprising an alcohol, a fatty acid, a fatty amine, and an amine having a structure N(R2)3, wherein R2 may be independently hydrogen or alkyl.
Advantageously, the polar solvent may facilitate the complete dissolution of the metal halide at high concentrations and thereby enable post-treatment of the core perovskite structure for doping or substitution with the metal halide. The polar solvent may further be miscible with low-polarity solvents that may be present in the mixing solvent to aid the dispersion of the core perovskite structure and/or the compound comprising silicon and oxygen. This may facilitate the mixing solvent to be a good homogeneous system for ion-doping and shelling process.
The method as defined above may be contrary to conventional wisdom, as non-polar or low polarity post treatment solutions may be typically used in conventional synthesis of perovskite nanocrystals to minimize potential damage to the perovskite nanocrystal structures. The use of a suitable polar solvent may adjust the hydrophilicity of the synthesized nanocrystal, so that the nanocrystals may be highly dispersible in water. Advantageously, the method as defined above may not only circumvent the issue of poor solubility of most metal halides in low polarity solvents. but may also enable doping or substitution with functional metal ions. Importantly, the method may enable self-repairing of the perovskite nanocrystals, thus ensuring high PLQY.
In another aspect, there is also provided a substrate comprising the nanocrystal as defined above, wherein the substrate may be selected from the group consisting of an aqueous solution, film, microcrystal, or bulk single crystal.
In another aspect, there is also provided the use of the nanocrystal as defined above or the substrate as defined above in LEDs, multi-photon imaging, full-colour displays, lasers, bioimaging, optoelectronics, spintronic devices, solar cells, memristors or as radiation detectors.
Advantageously, the combination of high performance, high stability and high dispersibility in water of the nanocrystals may be useful in the development of HPNCs for practical applications.
The following words and terms used herein shall have the meaning indicated:
The word “core-shell” refers to a structure in which the core is at least partially encapsulated by the shell, where the core and shell are two different materials.
The word “low-dimensional perovskite” refers to molecular-level or structure-level low-dimensional perovskite structures which are either perovskite structures a) made of the [BX6]4− octahedra that exist in a two-dimensional, one-dimensional or zero-dimensional form, as opposed to a three-dimensional form. They possess the dimension to one or several molecular units in at least one direction; or b) having a morphology of a nanoplatelet, nanosheet, nanowire, nanorods, nanocrystals or nanoclusters.
The word “doped” and “substituted” with respect to the metal halide in the nanocrystal as defined herein, may be used interchangeably, and refers to the intentional introduction of an impurity into the intrinsic perovskite for the purpose of modulating its electrical, optical and structural properties. The term “doping” and “substituting” should be construed accordingly.
The word “substantially” does not exclude “completely” e.g. a composition which is “substantially free” from Y may be completely free from Y. Where necessary, the word “substantially” may be omitted from the definition of the invention.
Unless specified otherwise, the terms “comprising” and “comprise”, and grammatical variants thereof, are intended to represent “open” or “inclusive” language such that they include recited elements but also permit inclusion of additional, unrecited elements.
As used herein, the term “about”, in the context of concentrations of components of the formulations, typically means +/−5% of the stated value, more typically +/−4% of the stated value, more typically +/−3% of the stated value, more typically, +/−2% of the stated value, even more typically +/−1% of the stated value, and even more typically +/−0.5% of the stated value.
Throughout this disclosure, certain embodiments may be disclosed in a range format. It should be understood that the description in range format is merely for convenience and brevity and should not be construed as an inflexible limitation on the scope of the disclosed ranges. Accordingly, the description of a range should be considered to have specifically disclosed all the possible sub-ranges as well as individual numerical values within that range. For example, description of a range such as from 1 to 6 should be considered to have specifically disclosed sub-ranges such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6 etc., as well as individual numbers within that range, for example, 1, 2, 3, 4, 5, and 6. This applies regardless of the breadth of the range.
Certain embodiments may also be described broadly and generically herein. Each of the narrower species and subgeneric groupings falling within the generic disclosure also form part of the disclosure. This includes the generic description of the embodiments with a proviso or negative limitation removing any subject matter from the genus, regardless of whether or not the excised material is specifically recited herein.
The accompanying drawings illustrate a disclosed embodiment and serve to explain the principles of the disclosed embodiment. It is to be understood, however, that the drawings are designed for purposes of illustration only, and not as a definition of the limits of the invention.
There is provided a nanocrystal having a core-shell structure, wherein the core of the core-shell structure is at least partially encapsulated by the shell of the core-shell structure, wherein:
A may be selected from the group consisting of CH3NH3+, CH(NH2)2+, Cs+, Rb+ and any mixture thereof, B may be selected from the group consisting of Pb2+, Sn2+, Ge2+ and any mixture thereof, and X may be selected from the group consisting of I−, Br−, Cl−, F− and any mixture thereof.
The monovalent, divalent or trivalent metal ion may be an ion of a metal selected from the group consisting of Group IA, Group IIA, Group IIIA or Group IVA of the Periodic Table of Elements, transition metal, lanthanoid series, actinoid series and any mixture thereof.
The monovalent, divalent or trivalent metal ion may be selected from the group consisting of Na+, K+, Rb+, Ca2+, Sc3+, Cu+, Ga3+, Cd2+, Sn2+, Mn2+, Y3+, Zn2+, In3+, Ni2+, Co2+, Al3+, Mg2+, Fe2+, Fe3+, Pb2+, Bi3+, La3+, Ce3+, Pr3+, Nd3+, Pm3+, Sm3+, Eu3+, Gd3+, Tb3+, Dy3+, Ho3+, Er3+, Tm3+, Yb3+, Lu3+ and any mixture thereof.
For ion doping or substitution in the shell perovskite structure, the monovalent, divalent or trivalent metal ion may improve the functionality of the nanocrystal. Doping or substitution at the A-site (group IA elements of the Periodic Table of Elements) and X-site (halide ions) of the structure ABX3 may be mainly responsible for adjusting the band gap or emission band, while doping or substitution at the B-site of the structure ABX3 (except with group IA elements of the Periodic Table of Elements and non-metal elements) may provide additional function to the nanocrystal.
The ion of the metal selected from Group IA of the Periodic Table of Elements may be doped in the A-site of the shell perovskite structure.
The ion of the metal selected from Group IIA, IIIA or IVA of the Periodic Table of Elements, transition metal, lanthanoid series or actinoid series may be doped at the B-site of the shell perovskite structure.
For example, doping with Yb3+ may alter f-f transitions and therefore may be useful in quantum cutting applications as it may yield about 200% PLQY in the near-infrared emission, while doping with ions of rare-earth elements may be useful in sensing. Similarly, doping with Mn2+ and ions of the iron triad (Fe2+, Fe3+, Ni2+ and Co2) may alter d-d transition emission and magnetic properties and therefore may be useful in spintronics application.
The doping with the metal halide may independently occur on the surface of the core of the core-shell structure, the surface of the core perovskite structure, in the shell of the core-shell structure, in the shell perovskite structure, in the low-dimensional perovskite structure, or any mixture thereof. The shell of the core-shell structure may comprise the shell perovskite structure and the compound comprising silicon and oxygen. The doping may generally occur in the perovskite structure.
The low-dimensional perovskite shell may further comprise a halide ion X′− selected from the group consisting of I−, Br−, Cl−, F− or any mixture thereof.
The halide ion in the low-dimensional perovskite shell may advantageously improve spectral tunability of the nanocrystal. The nanocrystal, depending on the halide used to dope the low-dimensional perovskite structure, may emit across the full colour spectrum, namely between about 350 nm to about 750 nm. By using chlorinated, brominated, or iodinated metal salts, nanocrystals with blue, green or (deep) red emission, respectively may be obtained.
The ratio of the metal ion and halide ion doped in the nanocrystal may not directly correlate to the stoichiometric ratio of the elements comprising the metal halide. The doping amount of the metal ion and halide ion may independently be affected by many factors, including concentration. temperature, volume of doping element and its suitability in the nanocrystal, including valence. As an example, if the nanocrystal is doped with YCl3, doping with one Y3+ ion may not necessarily entail doping with 3 Cl− ions.
The low-dimensional perovskite structure in the shell perovskite structure may be selected from the group consisting of a zero-dimensional perovskite structure, one-dimensional perovskite structure, two-dimensional perovskite structure and any mixture thereof.
The core perovskite structure may comprise three-dimensional γ-CsPbX3.
The core perovskite structure may comprise substantially of γ-CsPbX3. The core perovskite structure may comprise greater than 95 wt %, greater than 97 wt % or greater than 99 wt % of γ-CsPbX3. The core perovskite structure may contain small amounts (less than 5 wt %) of impurities such as Cs4PbBr6 which may have been introduced by batch error or room temperature synthesis without an insulating atmosphere. The amount of impurities in the core perovskite structure may be in the range of about 0 wt % to about 5 wt %, about 0 wt % to about 1 wt %, about 0 wt % to about 3 wt %, about 1 wt % to about 3 wt %, about 1 wt % to about 5 wt %, or about 3 wt % to about 5 wt %.
The low-dimensional perovskite structure may comprise a structure selected from the group consisting of zero-dimensional ABX3 magic sized clusters, zero-dimensional A4BX6, one-dimensional δ-ABX3, two-dimensional ABX3 nanoplatelets, two-dimensional AB3X5 and any mixture thereof.
The one-dimensional δ-ABX3 may be in the form of nanorods.
When the core perovskite structure comprises three-dimensional γ-CsPbX3, the low-dimensional perovskite structure may comprise a structure selected from the group consisting of zero-dimensional CsPbX3 magic sized clusters, zero-dimensional Cs4PbX6, one-dimensional δ-CsPbX3, two-dimensional CsPbX3 nanoplatelets, two-dimensional CsPb2X5 and any mixture thereof.
The presence of the low-dimensional perovskite structures as defined above may be a distinct fingerprint of the nanocrystal as defined above. The low-dimensional perovskite structure may comprise multiple forms of low-dimensional perovskite structures. Further, the low-dimensional perovskite structures in the shell perovskite structure may be different before and after dispersing the nanocrystal in water, or after doping with different metal halides.
When the nanocrystal is dispersed in a substrate such as water, the low-dimensional perovskite structure may become dispersed throughout the substrate.
When the nanocrystal is dispersed in a substrate such as water, the low-dimensional perovskite structure may comprise zero-dimensional CsPbX3 magic sized clusters (MSCs). The zero-dimensional CsPbX3 MSCs may have a size in the range of about 2 nm to about 4 nm, about 2 nm to about 3 nm or about 3 nm to about 4 nm.
Magic-sized clusters (MSCs) may be a specific molecular-scale arrangement of atoms that may exhibit enhanced stability. They may grow in discrete jumps, creating a series of crystallites, without the appearance of intermediate sizes.
The compound comprising silicon and oxygen may be selected from the group consisting of silica, silicate, an oligomeric silicon-oxygen compound, siloxane and any mixture thereof.
The nanocrystal may have a particle size in the range of about 40 nm to about 80 nm, about 40 nm to about 50 nm, about 40 nm to about 60 nm, about 40 nm to about 70 nm, about 50 nm to about 60 nm, about 50 nm to about 70 nm, about 50 nm to about 80 nm, about 60 nm to about 70 nm, about 60 nm to about 80 nm or about 70 nm to about 80 nm.
The core of the core-shell structure of the nanocrystal may have a size in the range of about 10 nm to about 30 nm, about 10 nm to about 15 nm, about 10 nm to about 20 nm, about 10 nm to about 25 nm, about 15 nm to about 20 nm, about 15 nm to about 25 nm, about 15 nm to about 30 nm, about 20 nm to about 25 nm, about 20 nm to about 30 nm, or about 25 nm to about 30 nm.
The core of the core-shell structure may all have the same size as defined above. Having the size as defined above may reduce energy dissipation due to size dispersion in the nanocrystals. This may enable the perovskite nanocrystals to achieve optical gain (or stimulated emission) more easily. That is, the nanocrystal may achieve low threshold simulated emission.
There is also provided a process of preparing the nanocrystal as defined above, comprising a step of simultaneously mixing in a mixing solvent, a core perovskite structure having a formula ABX3, a metal halide comprising a monovalent, divalent or trivalent metal ion and a precursor compound comprising silicon and oxygen, wherein:
Prior to the mixing step, the process may further comprise the step of dissolving the metal halide in a polar solvent comprising an alcohol, a fatty acid, a fatty amine, and an amine having a structure N(R2)3, wherein R2 may be independently hydrogen or alkyl.
The polar solvent may comprise about 50% to about 80%, about 50% to about 60%, about 50% to about 70%, about 60% to about 70%, about 60% to about 80%, or about 70% to about 80% by volume of the alcohol,
The polar solvent may comprise about 15% to about 25%, about 15% to about 17%, about 15% to about 20%, about 15% to about 22%, about 17% to about 20%, about 17% to about 22%, about 17% to about 25%, about 20% to about 22%, about 20% to about 22% or about 22% to 25% by volume of the fatty acid
The polar solvent may comprise about 5% to about 15%, about 5% to about 7%, about 5% to about 10%, about 5% to about 12%, about 7% to about 10%, about 7% to about 12%, about 7% to about 15%, about 10% to about 12%, about 10% to about 15% or about 12% to about 15% by volume of the fatty amine
The polar solvent may comprise and about 1% to about 3%, about 1% to about 1.5%, about 1% to about 2%, about 1% to about 2.5%, about 1.5% to about 2%, about 1.5% to about 2.5%, about 1.5% to about 3%, about 2% to about 2.5%, about 2% to about 3% or about 2.5% to about 3% by volume of the amine having the structure N(R2)3.
The total volume of the polar solvent may add to 100%.
The alcohol may be selected from the group consisting of methanol, ethanol, isopropanol and any mixture thereof.
The fatty acid may be a C2 to C20 fatty acid. The fatty acid may be a saturated or unsaturated fatty acid. The fatty acid may be a monounsaturated fatty acid. The fatty acid may be oleic acid, dodecanoic acid, octanoic acid, hexanoic acid, acetic acid, or any mixture thereof.
The fatty amine may be a C5 to C20 fatty amine. The fatty amine may be a saturated or unsaturated fatty amine. The fatty amine may be a monounsaturated fatty amine. The fatty amine may be oleylamine, dodecylamine, octylamine, hexylamine or any mixture thereof.
The amine having a structure N(R2)3, wherein R2 may be independently hydrogen or alkyl, may be selected from the group consisting of ammonia, methylamine, dimethylamine, trimethylamine, ethylamine, diethylamine, triethylamine, and any mixture thereof.
The polar solvent may comprise oleic acid, oleylamine, ammonia and an alcohol selected from the group consisting of methanol, ethanol, isopropanol and any mixture thereof.
The metal halide may be selected from the group consisting of NaX′, KX′, RbX′, CaX′2, ScX′3, CuX′, GaX′3, CdX′2, SnX′2, MnX′2, YX′3, ZnX′2, InX′, NiX′2, CoX′2, AlX′3, MgX′2, FeX′2, FeX′3, PbX′2, BiX′3, LaX′3, CeX′3, PrX′3, NdX′3, PmX′3, SmX′3, EuX′3, GdX′3, TbX′3, DyX′3, HoX′3, ErX′3, TmX′3, YbX′3, LuX′3, and any mixture thereof, wherein X′ is independently selected from Cl, Br, I or F.
The metal halide may be present at a concentration in the range of about 0.1 mM to about 400 mM, about 0.1 mM to about 0.4 mM, about 0.1 mM to about 1 mM, about 0.1 mM to about 4 mM, about 0.1 mM to about 10 mM, about 0.1 mM to about 40 mM, about 0.1 mM to about 100 mM, about 0.4 mM to about 1 mM, about 0.4 mM to about 4 mM, about 0.4 mM to about 10 mM, about 0.4 mM to about 40 mM, about 0.4 mM to about 100 mM, about 0.4 mM to about 400 mM, about 1 mM to about 4 mM, about 1 mM to about 10 mM, about 1 mM to about 40 mM, about 1 mM to about 100 mM, about 1 mM to about 400 mM, about 4 mM to about 10 mM, about 4 mM to about 40 mM, about 4 mM to about 100 mM, about 4 mM to about 400 mM, about 10 mM to about 40 mM, about 10 mM to about 100 mM, about 10 mM to about 400 mM, about 40 mM to about 100 mM, about 40 mM to about 400 mM, or about 100 mM to about 400 mM.
In the mixing solvent, the metal halide may be present at a concentration in the range of about 0.3 mM to about 10 mM, about 0.3 mM to about 0.5 mM, about 0.3 mM to about 1 mM, about 0.3 mM to about 5 mM, about 0.5 mM to about 1 mM, about 0.5 mM to about 5 mM, about 0.5 mM to about 10 mM, about 1 mM to about 5 mM, about 1 mM to about 10 mM, or about 5 mM to about 10 mM.
In the polar solvent, the metal halide may be present at a concentration in the range of about 20 mM to 400 mM, about 20 mM to about 40 mM, about 20 mM to about 100 mM, about 20 mM to about 200 mM, about 40 mM to about 100 mM, about 40 mM to about 200 mM, about 40 mM to about 400 mM, about 100 mM to about 200 mM, about 100 mM to about 400 mM or about 200 mM to about 400 mM.
The precursor compound comprising silicon and oxygen may be selected from the group consisting of tetramethylorthosilicate (TMOS), tetraethylorthosilicate (TEOS), tetraisopropyl orthosilicate (TIPOS), (3-aminopropyl)triethoxysilane (APTES) and any mixture thereof.
The precursor compound comprising silicon and oxygen may be present at a concentration in the range of about 2 mM to about 10 mM, about 2 mM to about 4 mM, about 2 mM to about 6 mM, about 2 mM to about 8 mM, about 4 mM to about 6 mM, about 4 mM to about 8 mM, about 4 mM to about 10 mM, about 6 mM to about 8 mM, about 6 mM to about 10 mM or about 8 mM to about 10 mM.
Prior to the mixing step, the process may further comprise the step of size-sieving the core perovskite structure to a size in the range of about 10 nm to about 30 nm, about 10 nm to about 15 nm, about 10 nm to about 20 nm, about 10 nm to about 25 nm, about 15 nm to about 20 nm, about 15 nm to about 25 nm, about 15 nm to about 30 nm, about 20 nm to about 25 nm, about 20 nm to about 30 nm, or about 25 nm to about 30 nm.
The step of size-sieving may be performed by centrifugation.
The size-sieving of the core perovskite structure to the size as defined above before silica encapsulation may reduce energy dissipation due to size dispersion in the nanocrystals. This may enable the perovskite nanocrystals to achieve optical gain (or stimulated emission) more easily. That is, the nanocrystal may achieve low threshold simulated emission. In contrast, when encapsulation with the silicon-oxygen compound is simultaneously accompanied by the nucleation and growth of the perovskite nanocrystals, it may be difficult to perform size sieving by means of centrifugation and thereby develop perovskite nanocrystals as low threshold optical gain medium.
The core perovskite structure may be present at a concentration in the range of about 25 nM to about 70 nM, about 25 nM to about 30 nM, about 25 nM to about 30 nM, about 25 nM to about 40 nM, about 25 nM to about 50 nM, about 25 nM to about 60 nM, about 30 nM to about 40 nM, about 30 nM to about 50 nM, about 30 nM to about 60 nM, about 30 nM to about 60 nM, about 40 nM to about 50 nM, about 40 nM to about 60 nM, about 40 nM to about 70 nM, about 50 nM to about 60 nM, about 50 nM to about 70 nm, or about 60 nM to about 70 nM.
The mixing solvent may comprise a solvent selected from the group consisting of an alcohol, a fatty acid, a fatty amine, n-hexane, toluene, dichloromethane, an amine having a structure N(R2)3 wherein R2 is independently hydrogen or alkyl, and any mixture thereof.
The mixing step may be performed at a temperature in the range of about 25° C. to about 35° C., about 25° C. to about 27° C., about 25° C. to about 30 ° C., about 25° C. to about 32° C., about 27° C. to about 30° C., about 27° C. to about 32° C., about 27° C. to about 35° C., about 30° C. to about 32° C., about 30° C. to about 35° C. or about 32° C. to about 35° C.
The mixing step may be performed for a duration in the range of about 1 hour to about 36 hours, about 1 hour to about 6 hours, about 1 hour to about 12 hours, about 1 hour to about 24 hours, about 6 hours to about 12 hours, about 6 hours to about 12 hours, about 6 hours to about 24 hours, about 6 hours to about 36 hours, about 12 hours to about 24 hours, about 12 hours to about 36 hours, or about 24 hours to about 36 hours.
There is also provided a substrate comprising the nanocrystal as defined above, wherein the substrate may be selected from the group consisting of an aqueous solution, film, microcrystal, or bulk single crystal.
The film may comprise a polymer selected from the group consisting of polymethyl methacrylate, polyethylene, polyethylene terephthalate (PET), polypropylene (PP), polydimethylsiloxane (PDMS) and any mixture thereof.
There is also provided the use of the nanocrystal as defined above or the substrate as defined above in LEDs, multi-photon imaging, full-colour displays, lasers, bioimaging, optoelectronics, spintronic devices, solar cells, or as radiation detectors.
The bioimaging may be multi-colour and/or multi-functional imaging. In bioimaging, the nanocrystal as defined above may be used as a high fluorescent biomedical label.
The laser may be a low-threshold multi-colour laser.
Non-limiting examples of the invention will be further described in greater detail by reference to specific Examples, which should not be construed as in any way limiting the scope of the invention.
Lead bromide (22 98%), cesium bromide (99.999%), oleylamine (70%), oleic acid (90%), methyl acetate (anhydrous, 99.5%), ethyl acetate (anhydrous, 99.8%), hexane (anhydrous, 95%), toluene (anhydrous, 99.8%), N,N-dimethylformamide (anhydrous, 99.8%), dimethyl sulfoxide (anhydrous, ≥99.9%), ammonium hydroxide solution (28% NH3 in H2O, ≥99.99%), ethyl alcohol (anhydrous, >99.5%), isopropyl alcohol (anhydrous, 99.5%), tetraethyl orthosilicate (99.999%), tetraisopropyl orthosilicate and metal halides for post-treatment were purchased from Sigma-Aldrich (St. Louis, Missouri, USA). Tetramethyl orthosilicate (>99.0%) was purchased from Tokyo Chemical Industry Co., Ltd (TCI, Tokyo, Japan). Reagents were used as such unless until mentioned further purification.
Fourier-transform infrared (FTIR) spectroscopy spectra were taken in attenuated total reflection mode (ATR) using a commercial FTIR spectrometer (Invennio-R, Bruker, Billerica, Massachusetts, USA) equipped with diamond ATR accessory. The setup was constantly purged with dry N2 gas.
X-ray photoelectron spectroscopy (XPS) measurements were conducted using an XPS Shimadzu Kratos Axis Supra (Shimadzu, Kyoto, Japan), with XPS peak information analysed via the National Institute of Standards and Technology (NIST) X-ray Photoelectron Spectroscopy Database. Powder X-ray Diffraction (PXRD) patterns were measured using a PANalytical X'Pert Pro X-ray diffraction system (PANalytical Inc., Malvern, UK) with monochromatic Cu Kα irradiation (λ=1.5418 Å).
The High-Resolution Transmission Electron Microscopy (HR-TEM) and High-Angle Annular Dark-Field Scanning Transmission Electron Microscopy (HAADF-STEM) images were recorded in a ARM300 TEM (JEOL, Tokyo, Japan) equipped with a probe and an image corrector. The HAADF-STEM images were recorded with a 90 mrad semi-angle inner collection angle. The Scanning Transmission Electron Microscopy Energy Dispersive X-ray (STEM-EDX) signal was recorded using a JEOL-EDX detector installed on the ARM300 TEM (JEOL, Tokyo, Japan). The HAADF-STEM and STEM-EDX data were collected at cryogenic temperature to mitigate the contamination using a dedicated micro-electromechanical system (MEMS) based Transmission Electron Microscopy (TEM) holder with improved spatial stability. The spatial drift of the STEM-EDX stack was compensated by realigning the EDX stack using HyperSpy Python plugin.
The optical measurements for multiphoton excited femtosecond transient absorption (TA) experiments were performed by using a Phasetech spectrometer (PhaseTech Spectroscopy. Inc., Madison. Wisconsin, USA). The Near Infrared (IR) pump pulse was generated from an optical parametric amplifier (NDFG, Light Conversion) that was pumped by a 1 kHz regenerative amplifier (Astrella, Coherent Inc. (Santa Clara, California. USA), 35 fs, 1 kHz, 800 nm), with 3.5 mJ input pulse energy. The system was seeded by a mode-locked Ti-sapphire oscillator (Vitesse. Coherent Inc., 80 MHZ). The white light continuum probe beam was generated by focusing a small portion (about 10 μJ) of the regenerative amplifier's fundamental 800 nm laser pulses into a 2 mm sapphire crystal (for visible range). The probe beam was collected using a Charge-coupled device (CCD) sensor (Teledyne e2v. Chelmsford, UK). Time-Resolved Photoluminescence (TRPL) measurements were performed using excitation pulses from the same femtosecond laser system described above. The luminescence signal from the sample was dispersed by a DK240) 1/4 meter monochromator with 150 g mm−1 grating, and the temporal evolution of the photoluminescence (PL) was resolved by an Optoscope streak camera system (Optronics, Kehl, Germany), which has an ultimate temporal resolution of about 10 ps when operated at the shortest time window of 330 ps. Steady-state absorption spectra were collected using a UV-3600 UV-VIS-NIR spectrophotometer (Shimadzu. Kyoto. Japan). Photoluminescence Quantum Yield (PLQY) and Commission Internationale de I'Elcairage (CIE, the International Commission on Illumination) chromaticity measurements were performed using a Jobin-Yvon Fluorolog system (Horiba, Kyoto, Japan) equipped with iHR320 monochromator, coupled with a photomultiplier tube and a spectrally calibrated Spectralon-coated integrating sphere (Quanta-Phi, Lauderdale, Florida, USA). Excitation energy was varied by selecting different components of a Xe lamp emission with a monochromator. Dilute solutions of the samples were contained in a quartz 1 cm×1 cm cuvette.
Caenorhabditis elegans (C. elegans) maintenance and assessment of HPNCs toxicity and in-vivo PL imaging are as follows. The C. elegans wild-type strain (purchased from University of Minnesota Caenorhabditis Genetics Center) was used in all toxicity experiments. C. elegans were maintained on Nematode Growth Medium (NGM) agar plates seeded with Escherichia coli OP50 as food source at 20° C. Worms were synchronized by bleaching in all experiments. A stock solution of 4 mg/ml HPNCs diluted in ultrapure water was prepared and diluted accordingly (from 0.01 mg/mL to 0.5 mg/mL) for various experiments. Toxic effects were assessed by three factors which were body length. locomotion, and reproduction rate. There was negligible toxic effects on the C. elegans animal model at concentrations of up to 0.5 mg/mL HPNCs in toxicity endpoint assays. Bright field images were acquired with Lumar. V12 stereomicroscope (Carl Zeiss AG, Oberkochen, Germany). The worm length was measured using ImageJ software. Locomotion behaviours were assessed by counting worm body thrashes in liquid M9 media. Fifty age-synchronized adult worms were seeded on NGM agar-coated 12-well plates. Reproductive rates were obtained by counting the number of eggs per well 5 days after seeding and exposure to HPNCs. Each experiment noted above was independently repeated three times. In-vivo PL imaging was taken by the Carl Zeiss inverted fluorescence microscope, and were performed after C. elegans ingested HPNCs for 10 minutes.
Single-photon to multi-photon excited bioimaging was conducted using a 1035 nm femtosecond pulse as the excitation (50 MHz, pulse width about 260 fs) generated from a fully automated ultrafast laser system (Monaco 1035-80-60, Coherent, Inc., Santa Clara, California, USA). In addition, the 400 nm (3.1 eV, 250 kHz, <160 fs) excitation pulse was generated in optical parametric amplifier (Coherent Inc., OPA 9400/9800 series) by simply frequency doubling the 800 nm femtosecond pulses with BBO nonlinear crystal. The 800 nm femtosecond pulses were generated from regenerative amplifier (Coherent Inc., RegA 9000, 250 kHz, <160 fs), which used a Verdi G for CW pumping and Vitara for seed pulses. The incident 400 nm or 1035 nm laser beam was directly coupled to the Nikon C2si-SH C2 Scanner mounted on the Nikon Ti2-E Inverted Motorized Microscope (Nikon, Tokyo, Japan), then focusing on the sample through an objective lens (CFI TU Plan FLUOR Epi 20×, NA/WD: 0.45/4.5 mm). Photo multiplier tubes (PMTs) were used to collect PL signals from the sample for imaging. In addition, the bright field images were taken by a CMOS camera (Zelux® 1.6 MP CMOS Cameras, Thorlabs, Inc., New Jersey, USA) mounted on the microscope. Various functions for bioimaging such as high dynamic range (HDR) mode, Z-stack scanning, and 3D displaying modes were obtained from Nikon NIS-Elements C Software Suite.
In order to determine the multi-photon absorption cross section (MPAC, σn, where n is the order of MPE) of these aqueous HPNCs, the transient absorption (TA) saturation method was developed to uniformly solve the measurement of single- to multi-photon excitation. This was a method for directly measuring the multiphoton absorption cross section, which was different from the existing commonly used multiphoton excited PL ratio method that can only perform indirect measurement.
By analysing the bleaching signal |ΔOD|t
in which, α is a constant that relates to instrumental and sample parameters. N
refers to the average number of photons (for single photon excitation) or equivalent high-energy photons (for multiphoton excitation) absorbed per QD at the given excitation fluence. σn (n=1, 2, 3, 4, 5, . . . ) refers to the single-/multi-photon absorption cross-section (in cm2n sn−1photons1−n), and Fn refers to the photon fluence for single photon excitation or equivalent photon fluence for multiphoton excitation (in cm−2photonsns1−n) at the given excitation wavelength.
Further, Ppeak is the peak power density, ℏω is the photon energy for excitation and τ is the laser pulse width. By plotting Fn and |ΔOD|t
CsPbBr3 nanocrystals were first synthesized as the template before performing post-treatment with a metal halide salt solution and tetramethyl orthosilicate (TMOS) simultaneously to achieve full-colour emitting halide perovskite nanocrystals (HPNCs) with both high photoluminescence quantum yield (PLQY), stability and dispersibility in water. In contrast to conventional methods where organic halides with high solubility is used in low-polar solvents for post-treatment of perovskite nanocrystals to tune the emission spectrum, in the present disclosure, a mixed polar solvent system of alcohol/oleic acid (OAc)/oleylamine (OAm)/ammonia was used to prepare a clear solution of metal halide salts with high concentration (0.02 to 0.4 M) for post-treatment.
This method contravened conventional wisdom, as non-polar or low polarity solvents are typically used in these post-treatment steps instead of a polar solvent, to minimize any potential damage to the HPNCs. Surprisingly, this method not only overcame the issue of poor solubility of most metal halides such as MnCl2, YbCl3, CoX2, and InX3, where X=Cl−, Br−, I−, in low-polar solvents, but also allowed effective functional ion doping or substitution of the shell structure. More importantly, the method enabled self-repairing of the thus produced HPNCs, and resulted in the formation of a halogen-rich, low-lead, low-dimensional perovskite shell layer on the surface of the template CsPbBr3. This perovskite shell layer bound with the silicon-oxygen compound provided by the hydrolysis of TMOS, to synergistically facilitate stronger passivation and better protection from environmental stressors such as water, oxygen, heat or irradiation, as well as to improve the dispersibility of the nanocrystals in water and to reduce the toxicity of the nanocrystals (
CsPbBr3 nanocrystals (NCs) were synthesized by the ligand-assisted re-precipitation (LARP) method. Briefly, PbBr2 (73.4 mg, 0.2 mmol), CsBr (42.6 mg, 0.2 mmol), oleic acid (0.5 mL), and oleylamine (0.25 mL) were added to 5 mL dimethylformamide (DMF) or a (9:1) v/v DMF/Dimethyl sulfoxide (DMSO) mixed solution and stirred to be fully dissolved. A portion (1 mL) of the obtained mixture was swiftly injected into 10 mL toluene under vigorous stirring. After stirring, the resultant solution was subjected to a combination of centrifugation, which removed small-sized crystals at high speed (8000 rpm for 10 minutes) and large-sized crystals at low speed (3000 rpm for 15 minutes). The final size-sieved nanocrystals were stored in n-hexane for further use.
0.1 to 2.0 mmol metal halide salts (MnCl2, ZnCl2, NdBr3, MnI2, MgI2, RbBr, CoBr2, YCl3, YbCl3, InBr3, NiI2, InI3, AlI3 or ZnI2) were added to 5 mL of a mixed solution (alcohol:oleic acid:oleylamine:ammonia solution=34:10:5:1 by volume) and stirred to be fully dissolved for further use. In the present disclosure, the number following the metal halide in the sample name refers to the molar amount of metal halide used. For example, “InBr3-0.5” means that 0.5 mmol of InBr3 was used to prepare the metal halide solution for post-treatment, and the solution was prepared as described above.
Synthesis of the Aqueous Perovskite Nanocrystals with Metal Halide and TMOS Post-Treatment
0.2 mL metal halide solution and 5 μL tetramethyl orthosilicate (TMOS) were added to 10 mL of the approximately 60 nM template CsPbBr, nanocrystals solution and stirred for 2 to 24 hours at room temperature. Then the resultant solution was mixed with ethyl acetate at a volume ratio of 1:1 and centrifuged to obtain a precipitate. Finally, after drying, the precipitate was directly dispersed in water to form an aqueous perovskite nanocrystal solution. It should be noted that in the present disclosure, (½) in the sample name, for example “MnCl2-1.0 (½)”, means that the concentration of the template CsPbBr3 solution used in this sample is half of the approximately 60 nM template CsPbBr3 nanocrystal solution.
The template CsPbBr3 nanocrystals were synthesized by the facile, ligand-assisted re-precipitation (LARP) method. Basic characterization including high resolution transmission electron microscopy (HRTEM), absorption and photoluminescence (PL) spectra, as shown in
These perovskite nanocrystals were easily dispersed in water and gave strong emission with high colour purity and wavelength, which was adjustable from about 420 nm to about 670 nm. depending on the metal halide used in the post-treatment. The tunning of the emission properties of these nanocrystals originated from treatment with different metal halide solutions.
Both the A-site ion (alkali metal) and X-site ion (halogen) were mainly responsible for causing band gap adjustment. For example, Cl−, Br− or I− treatment causing doping or substitution provided blue, green, or red emission due to doping or substitution at the X-site; while B-site ions (except elements in Group IA of the Periodic Table of Elements and non-metal elements) provided additional emission bands, such as the d-d transitions of transition metals. For example. Mn emission of 500 to 700 nm that is evident in
Apart from the different spectral widths of both the transient absorption (TA) bleach and PL emission bands, pseudo-colour TA spectra of pristine CsPbBr3 NCs in toluene and HPNCs treated with representative metal halides, specifically YCl3 for blue-emission, InBr3 for green-emission and NiI2 for red-emission, and TMOS, as measured in water were rather similar, all showing an initial carrier cooling stage within 2 ps at low pump fluence (P), photoinduced bleach bands for delay times within 4 ns (
Detailed TRPL decay curves are shown in
Further, the introduction of water was thought to contribute to the formation of CsPb2Br5 given that the phase of CsPb2Br5 was more pronounced while the main peak of the CsPbBr3 phase was slightly weakened after being dispersed in water.
Using metal chloride (or iodide) for post-treatment, it was found that the diffraction peak of the pristine CsPbBr3 was still present although it had shifted to a larger angle (or a smaller angle). This was because the lattice constant became smaller (or larger) after being doped with chloride (or iodide) ions.
Interestingly and unexpectedly, the HPNC samples that were post-treated with metal halide and TMOS showed periodic diffraction peaks in the low-angle region (3° to 15°), which was attributed to the formation of low-dimensional perovskites. For the HPNC samples that used lead halide or metal iodide for post-treatment, these small-angle periodic peaks only appeared after being dispersed in water, but they were both weak and difficult to distinguish. This may be because the lead-rich surface was easier to construct high-dimensional structures, while iodide ions were not suitable for stabilizing low-dimensional structures due to their large volume.
In contrast, the non-lead metal bromide and chloride post-treated HPNCs (HPNCs treated with TMOS and InBr3-0.5 or MnCl2-1.0 (½)) showed significant periodic peaks either before or after the introduction of water. In particular, the peak position/intensity of the former was basically unchanged, indicating a high structural stability.
High-resolution electron transmission microscopy (HRTEM) further confirmed that the sample of HPNC treated with InBr3-0.5 and TMOS, before dispersion in water, had a core-shell structure (
The FFT pattern of the HRTEM image of the core (
The nanocrystals were also imaged using high-angle annular-dark-field (HAADF) scanning TEM (STEM) mode coupled with energy dispersive X-ray spectroscopy (EDX) to map the composition of the core-shell structure. It was found that the core had a brighter contrast than the shell in HAADF-STEM mode, indicating a higher density in the core compared to the shell. The EDX mapping indicated that the core had a higher concentration of Pb while Cs and Br were distributed more evenly throughout the particle (
The full scan X-ray photoelectron spectroscopy (XPS) spectra of HPNCs treated with TMOS and representative metal halides (PbBr2-0.2, InBr3-0.5, MnCl2-1.0 (½) and NiI2-0.25) showed that peaks of Cs 3d, Pb 4f, Br 3d, Si 2p and O 1 s were observed in all cases, while In 3d, Mn 2p and Cl 2p, Ni 2p and I 3d were separately present in the three non-lead metal treated samples (
The higher binding energy (Si 2p of 102.8 eV and O 1 s of 533.7 eV) was attributed to the formation of a silica network structure, while the lower binding energy (Si 2p of 101.7 eV and O 1 s of about 532 eV) may be attributed to the Si—O—H or oligomeric Si—O structure and the oxygen from the ligand oleic acid, which were also confirmed by Fourier Transform infrared spectroscopy (FTIR) analysis.
All these XPS and FTIR findings echoed the aforementioned PXRD results. Combined with the analysis of the TEM results, they indicated that the structure of these HPNCs before water introduction should be: (a) the non-lead metal chloride/bromide and TMOS post-treatment tended to form a halogen rich low-dimensional perovskite shell, supplemented by oligomeric Si—O—Si and Si—OH structures, which may be the reason for the high dispersibility of the resultant HPNCs in water; and (b) the post-treatment of lead halide/metal iodide and TMOS was not suitable for the formation of low-dimensional perovskite shell, but favoured the formation of a highly polymerized Si—O—Si network structure that protected the perovskite core.
All the post-treated HPNCs showed outstanding stability performance regardless of whether there was formation of a low-dimensional perovskite shell supplemented with oligomeric Si—O—Si and Si—OH structures or a highly polymerized Si—O—Si structure, whereby the former was superior.
Furthermore, when an irradiation source (MF-2000W-LED) calibrated to be equivalent to 1 sun irradiation was used to continuously irradiate an aqueous solution of the HPNCs treated with InBr3-0.5 and TMOS for 24 hours, the PLQY was maintained at about 80% with the chromaticity remaining invariant, thereby validating high irradiation stability (
The excellent water/chromaticity/irradiation stability performances indicated that the low-dimensional perovskite shell supplemented with oligomeric Si—O—Si and Si—OH structures provided better passivation and protection than pure, highly polymerized Si—O—Si structure. For the HPNCs post-treated with blue and red emitting metal halide (chloride and iodide, respectively) and TMOS, the stability also dramatically improved. To date, there have not been any reports on the stability of chlorinated or iodinated perovskite NCs in aqueous solution.
The PLQY of HPNCs treated with MnCl2-1.0 and TMOS which had pure blue emitting peaks at about 462 nm approached 60% after being dispersed in water for more than 900 hours. For HPNCs treated with YCl3-1.0 and TMOS with emission centre wavelength at about 458 nm, the PLQY attained was about 40% (
For red-emitting HPNCs, after being dispersed in water for about 750 hours, the HPNC treated with NiI2-0.25 and TMOS with emission centre wavelength of about 600 nm had a PLQY of about 30% (
The lower defect tolerance of chloride perovskites and the ion migration in iodide perovskites resulted in lower PLQY than bromide perovskites. The HPNCs treated with MnCl2-1.0 (½) and TMOS with higher concentration of MnCl2 showed a maximum PLQY of only about 23% after being dispersed for 250 hours in water (
It was noted that the PLQY of most HPNCs treated with metal halide and TMOS increased after being dispersed in water (
The stable and bright full-range colour emitting HPNCs enabled extremely challenging MPE measurements to be performed directly in water, which was unprecedented due to the thigh pump fluence needed.
The commercially available quantum dots (QDs) CdSe/ZnS with the trade name of ED-C11-TOL-0560 from Evident Technologies was used as the reference sample to evaluate the reliability of this method.
The dynamics of the two-dimensional TA spectroscopy of multi-photon excitation was basically the same as that of single-photon excitation (
Combined with the absorbance spectrum of the reference sample, the molar absorption coefficient at first exciton was calculated to be α (545 nm) approximately 1.8×105 M−1cm−1 close to the value of approximately 1.0×105 M−1 cm−1 provided by Evident Technologies Inc and the σ2 (800 nm) of approximately 1.48×104 GM was also consistent with previously known data. Likewise, the TA spectral bleaching signals of the pristine CsPbBr3 NCs and aqueous HPNCs showed a saturation trend with increasing pump fluence under single-photon to multi-photon excitation, which could be highly fitted by Equation 1 to derive corresponding single-/multi-photon absorption cross-sections σn (
Upon multiphoton excitation, the steady-state/time-resolved emission band position and shape of the HPNCs were basically the same as those under single-photon excitation (
Table 1 summarizes the multiphoton action cross-sections (that is, σn×η) of the full-colour emitting HPNC aqueous solutions, which were 4 to 5 orders of magnitude larger than that of the most advanced organic molecules in dimethyl sulfoxide, and 1 to 4 orders of magnitude larger than that of aqueous solutions of inorganic semiconductor quantum dots (QDs) of elements in Groups II-VI of the Periodic Table of Elements, indicating that the nanocrystals disclosed herein may be a highly promising fluorophore labelling system for multi-photon microscopy applications.
aλem refers to the emission centre wavelength of the material.
bη refers to the PLQY.
c Method refers to the method for single-/multi-photon absorption cross-section measurement.
dSIDT refers to the static intensity-dependent transmission measurement.
e OAZ scans refers to the open-aperture Z scan measurement.
As a proof-of-concept (POC) of the potential of the aqueous HPNCs for multi-photon in-vivo imaging. Caenorhabditis elegans (C. elegans) ingested with aqueous HPNCs treated with InBr3-0.5 and TMOS were imaged. The worms were first starved for 24 hours prior to exposure to the HPNCs, as starved C. elegans are known to feed quickly and indiscriminately on small particles. Upon 488 nm continuous light excitation, the ingested HPNCs were detected inside the pharynx of the worms after being exposed to HPNCs for about 10 minutes. In a video that was taken, it was observed that these C. elegans moved with a whip-like motion (or sinusoidal locomotion) on an agar plate, indicating that C. elegans readily fed on the HPNCs on the nematode growth medium (NGM) agar plates. This also validated successful operation of real-time in-vivo fluorescence imaging.
To ascertain whether these HPNCs were harmful to living organisms, the body length, locomotion, and reproductive rate of C. elegans that ingested HPNCs were studied. It was found that the body length of C. elegans that ingested the HPNCs was comparable with the control sample (
A further investigation of C. elegans, which had initially ingested HPNCs for about 10 minutes. found that the autofluorescence of the organisms was severe under continuous light-excitation (
Furthermore, after being stored at 4° C. for 96 hours, the sample of C. elegans that ingested HPNCs still performed remarkably with high-quality MPE imaging in the high dynamic range (HDR) mode without observable PL quenching (
The nanocrystal as defined above may be useful in full-colour displays, lasers, bioimaging, optoelectronics, spintronic devices, solar cells, memristors or radiation detectors.
The method of combining halide salt post-treatment and silica encapsulation may also be extended to other perovskite systems, including organic-inorganic hybrid perovskites, two-dimensional layered perovskites, and double perovskites.
It will be apparent that various other modifications and adaptations of the invention will be apparent to the person skilled in the art after reading the foregoing disclosure without departing from the spirit and scope of the invention and it is intended that all such modifications and adaptations come within the scope of the appended claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 1020210741Q | Jul 2021 | SG | national |
| 10202201079R | Feb 2022 | SG | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/SG2022/050469 | 7/6/2022 | WO |
