Patent Application
20220213381
The field of the DISCLOSURE lies in active materials for light emitting elements useful for light source apparatus and projector devices.
The present disclosure relates to a light emitting element comprising emissive semiconductor nano(crystal)material(s) (NC).
The present disclosure also relates to a light source apparatus, comprising at least one light emitting element according to the present disclosure.
The present disclosure also relates to a projector device, comprising a light source apparatus, comprising at least one light emitting element according to the present disclosure.
Moreover, the present disclosure relates to methods of obtaining embedded semiconductor nano(crystal)material(s) and NC films.
The “background” description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description which may not otherwise qualify as prior art at the time of filing, are neither expressly or impliedly admitted as prior art against the present disclosure.
In recent years, projector devices using solid state light sources, e.g. light emiting diodes LED or laser diodes LD, have become state-of-the-art technology. In some projector devices, LD are used as direct light sources, while in other cases the light from LD or LED source is used to excite an emissive material which emits photoluminescencent light within a specific wavelength range due to the excitation by the LD or LED light source.
Known emissive materials comprise inorganic phosphor materials, e.g. yellow-green emitting yttrium-aluminium-garnet (YAG) based material, or a combination of red and green emitting phosphor materials. A disadvantage of state-of-the-art inorganic phosphor materials is their broad emission spectrum (e.g. for YAG-based materials). Especially the limited emission in the red compared to the green spectral region leads to limitations in the achievable colour rendering index.
Semiconductor emissive nanocrystals (NC) are being explored as (electro-) luminescent materials in several lighting applications, e.g. LED or OLED flat-panel displays, as well as an active material in emissive display color filters.
A new/emerging application of NC materials is as an emissive source in projector devices, where the usage of NC materials aims improving the luminous efficacy and the color gamut compared to state-of-the-art inorganic phosphor materials used to date. The advantage of NC for projector application is their narrow spectral emission (FWHM ˜20-40 nm), high internal quantum efficiency (quantum yield (QY) up to ˜95%), as well as the possiblity to tune the emission wavelength in the visible range by changing the composition and the structure of the NC.
In one approach to realize a NC-based projector emissive source, the nanocrystals are dispersed in a matrix (polymeric or inorganic) to form a thin composite film. The NC are excited by an incident laser beam with a specific wavelength and at specific excitation power and the resulting photoluminescent light is collected. Typically a NC content of a few volume percent in the film is needed in order to achieve sufficient external quantum efficiency of the NC source, and to reach the required brightness and color gamut of the projector light source.
The internal quantum efficiency of emissive—nanocrystals—has achieved nearly 100%. However, the external quantum efficiency of NC-based light source remains below 15% because of losses due to concentration dependent multi-particle effects, e.g. re-absorption of the emitted photoluminescent light, emission quenching due to resonant energy transfer between neighbouring NC particles QD or non-radioactive relaxation processes (e.g. Auger recombination) or thermal quenching due to heating of the NC.
Further, the photoluminescence of pristine NC materials is degrading within a few minutes to few hours upon excitation with high light flux used in projector light source (typically in the range of several Watt/cm2 to several kWatt/cm2). The limited photo stability of the native nanocrystals is attributed to degradation processes, e.g. oxidative processes caused by the presence of oxygen and/or humidity in the environment, as well as due to thermal degradation of the light-emissive NC material.
It is provided a light emitting element capable of obtaining a high output and having excellent structural stability, a light source apparatus including the light emitting element, and a projector.
The present disclosure provides a light emitting element, comprising emissive semiconductor nano(crystal)material(s).
The present disclosure provides a light source apparatus, comprising
(i) a light source, and
(ii) at least one light emitting element according to the present disclosure, or a plurality of light emitting elements according to the present disclosure.
The present disclosure provides a projector device, comprising
(i) a light source apparatus according to the present disclosure,
(ii) a light modulation element, and
(iii) a projection optical system.
The present disclosure provides a method of obtaining emissive semiconductor nano(crystal) material(s) (NC) encapsulated in a shell, comprising the steps of
The present disclosure provides a method of obtaining semiconductor nano(crystal) material(s) (NC) encapsulated in a monolith, comprising the steps of
The present disclosure provides a method of generating a thin layer or film comprising a NC material, a binder material, and optionally other additives, which are deposited on a substrate, said method comprising the steps of
The present disclosure provides a method of increasing the thermal conductivity of the light emitting element, comprising
(i) mechanical ad-mixing of high thermal conductivity materials to the NC/binder system, preferably as obtained with the method of generating a thin layer or film according to the present disclosure, or
(ii) co-incorporation of high-thermal conductivity materials and NC into the shell or monolith encapsulation matrix.
The foregoing paragraphs have been provided by way of general introduction, and are not intended to limit the scope of the following claims. The described embodiments, together with further advantages, will be best understood by reference to the following detailed description taken in conjunction with the accompanying drawings.
A more complete appreciation of the disclosure and many of the attendant advantages thereof will be readily obtained as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings, wherein:
The light emitting element (1) has the shape of a wheel and is a light emitting element in which a reflective layer (3, with a surface (3S)) and a layer of emissive semiconductor nano(crystal) material (4) comprising NC (5) (and optionally binder (6)) are laminated in order on a surface (2S) of a base material (2) including a thin plate having a circular planar shape an opening (2K) is provided at the center of the base material (2). Further details are enclosed in U.S. Pat. No. 9,645,479 B2.
The light emitting element (1A) is a light emitting element in which the layer of emissive semiconductor nano(crystal) material (4) is formed on a surface (2S1) of the base material 2. The surface (2S1) is a rough surface. The light emitting element (1A) is a so-called transmission type light emitting element: the base material (2) is configured of a transparent material and has a property of transmitting the excitation light (EL) with which a rear face (2S2) is irradiated on the side opposite to the surface (2S1).
Further details are enclosed in U.S. Pat. No. 9,645,479 B2.
The light source apparatus (10) includes the light emitting elements (1) and (1A), a motor (11) including a rotation axis (J11), a motor (11A) including a rotation axis (J11A), a light source part (12) emitting the excitation light (EL), lenses (13 to 16), a dichroic mirror (17), and a reflection mirror (18). The light emitting element (1) is rotatably supported by the rotation axis (J11) and the light emitting element (1A) is rotatably supported by the rotation axis (J11A). The light source part (12) includes a first laser group (12A) and a second laser group (12B). Both of the first and the second laser groups (12A) and (12B) are groups in which a plurality of semiconductor laser elements (121) which oscillate blue laser light as excitation light. Here, for convenience, the excitation light oscillated from the first laser group (12A) is referred to as (EL1) and the excitation light oscillated from the second laser group (12B) is referred to as (EL2).
Further details are enclosed in U.S. Pat. No. 9,645,479 B2.
The projector (100) includes the light source apparatus (10), the illumination optical system (20), an image forming part (30), and a projection optical system (40) in order.
The illumination optical system (20) includes, for example, a fly eye lens (21) (21A and 21B), a polarization conversion element (22), a lens (23), dichroic mirrors (24A and 24B), reflection mirrors (25A and 25B), lenses (26A and 26B), a dichroic mirror (27), and polarization plates (28A to 28C) from the position close to the light source apparatus (10).
The image forming part (30) includes reflection type polarization plates (31A to 31C), reflection type liquid crystal panels (32A to 32C), and a dichroic prism (33).
The projection optical system (40) includes lenses (L41 to L45) and a mirror (M40).
Further details are enclosed in U.S. Pat. No. 9,645,479 B2.
a) mechanical ad-mixing to the NC/binder system; and b) co-incorporation into the shell or monolith encapsulation matrix.
As discussed above, the internal quantum efficiency of semiconductor nanocrystals has achieved nearly 100%, whereas, the external quantum efficiency of the semiconductor nanocrystal based light source remains below ˜15% because of losses due to concentration dependent multi-particle effects, e.g. re-absorption of the emitted photoluminescent light, emission quenching due to resonant energy transfer between neighbouring nanocrystals or thermal quenching due to local heating of the nanocrystals.
Further, the photoluminescence of pristine emissive semiconductor nano(crystal) material is degrading within a few minutes to few hours upon excitation with high light flux used in projector source (typically in the range of several Watt/cm2 to several kWatt/cm2). The limited photo stability of the native NC is attributed to oxidative processes caused by the presence of oxygen and/or humidity in the environment, as well as due to thermal degradation of the light-emissive NC material.
To achieve both high photo stability and high efficiency of the NC-based projector light source, a modification of the native NC and their implementation into appropriate film matrix is required in order to prevent both oxidative and thermal degradation.
The present disclosure provides a light emitting element. Said light emitting element comprises emissive semiconductor nano(crystal) material(s) as described herein.
The light emitting element emits photoluminescent light, by being excited with light emitted from a light source, such as in a light source apparatus of the present disclosure or a projector device of the present disclosure.
In one embodiment, said emissive semiconductor nano(crystal) material(s) comprising elements of several groups of the periodic system, such as but not limited to:
(i) type II/VI semiconductor materials,
(ii) type BIN semiconductor materials,
(iii) group IV-VI elements,
(iv) group IB-(III)-VI elements,
(v) group IV elements,
(vi) organometallic halide perovskites,
In one embodiment, said emissive semiconductor nano(crystal)material(s) have dimensional structure(s), such as
micron sized particles,
nanostructured particles
sub-nanometer sized emissive clusters.
In one embodiment, the NC are encapsulated in non-emissive material(s)
(a) in a shell, or
(b) in a monolith.
In one embodiment of the light emitting element, the NC are encapsulated (a) in a shell, wherein the structure is preferably core/shell, or core/shell/shell, wherein the core is preferably a single NC.
The process of shell encapsulation aims for the formation of a core/shell NC material with an example structure as shown in
In said embodiment, the shell has a defined pore size, and the shell thickness is preferably in the range from 1 nm up to 1 μm.
Shell thickness can be between 1 nm and 1,000 nm, preferably between 20 nm and 100 nm. Shell porosity (expressed as minimum inner open voids size) is preferably between 0.001 nm and 0.5 nm.
Shell permeability to oxygen and humidity (expressed as oxygen transmission rate at 25° C. and 50% relative humidity) is preferably between 0.1 and 5 cm3/(m2 day)
In said embodiment, the shell material is a non-emissive material selected from
(i) inorganic oxide or nitride materials,
such as
(ii) polymer-based composite materials,
such as
The shell material has preferably a refractive index between 1 and 4, preferably between 1.2 and 2.5.
In said embodiment, the shell serves as a spacer to suppress resonant energy transfer between neighboring NC. The shell serves also as barrier to oxygen and/or humidity (H2O) permeation from the environment.
In one embodiment of the light emitting element, the emissive semiconductor nano(crystal) material(s) are encapsulated (b) in a monolith, wherein preferably several NCs (>1 NC/monolith) are embedded into a monolith matrix.
The process of monolith encapsulation aims the formation of a NC-containing material, with example structure shown in
Monolith Properties:
In said embodiment, the monolith material is a non-emissive material selected from
(i) inorganic oxide or nitride materials,
such as
(ii) polymer-based materials,
such as
(iii) single crystals,
such as
In one embodiment, the emissive semiconductor nano(crystal) material(s), preferably quantum dots (QD) further comprise support ligands.
In order to ensure high quantum yield (>50%) of the encapsulated NC, support ligands are preferably used to reduce the decrease of internal quantum efficiency (QY) during the encapsulation in shell and/or monolith.
In one embodiment, the support ligands are directly ad-mixed to the encapsulation reaction mixture during the encapsulation process and allowed to react with the NC nanocrystals typically before the shell or monolith formation.
In one embodiment, the support ligands are separately reacted with the initial NC material before encapsulation. In this case, a protective ligand shell on the NC is formed which is not exchanged during the encapsulation process, i.e. during the shell or monolith formation.
In said embodiment, said support ligands are added during encapsulation, or they form a ligand shell on the NC.
In said embodiment, the support ligands comprise:
(i) organic ligands,
such as
(ii) inorganic ligands,
such as
(ii) inorganic ligands,
such as
In one embodiment, the light emitting element further comprise high-thermal conductivity material(s).
In said embodiment, said high-thermal conductivity material(s) are preferably co-incorporated into the shell or monolith encapsulation matrix together with the emissive semiconductor nano(crystal) material.
The high-thermal conductivity materials preferably comprise:
inorganic oxide materials,
ceramic materials,
carbon-based materials,
In one embodiment of the light emitting element, the emissive semiconductor nano(crystal) (NC) material(s) are deposited as a thin layer or film, comprising NC and binder material, on a substrate.
For preparation of the light emitting element, emissive semiconductor nano(crystal) material(s) are preferably deposited as a thin layer comprising both NC and binder material.
In said embodiment the thickness of the layer or film can be in the range of 1 μm to 1,000 μm, preferably 10 μm to 200 μm.
In said embodiment the loading of NC can be in the range of 0.0001% vol up to 95% vol, preferably between 0.01% vol and 80% vol.
In said embodiment the binder material(s) can be selected from, but are not limited to:
silicone resin polymers
siloxane polymers,
thermoplastic polymers,
organic-inorganic silica polymers,
inorganic polysilazanes,
ceramic materials,
composite materials,
In one embodiment, the thermal conductivity of the thin layer or film of the light emitting element can be in the range from about 1 W/K.m to more than 30 W/K.m. Said thermal conductivity serves to achieve good thermal dissipation within the light emitting element.
In one embodiment, high thermal conductivity material(s) are mechanically admixed to the NC/binder system.
The high-thermal conductivity materials preferably comprise:
inorganic oxide materials,
ceramic materials,
carbon-based materials,
In one embodiment, the light emitting element further comprises a substrate material having a reflective surface.
As discussed above, the present disclosure provides a light source apparatus, comprising
(i) a light source, and
(ii) at least one light emitting element according to the present disclosure, or a plurality of light emitting elements according to the present disclosure.
In one embodiment, the light source is a laser diode, preferably a blue laser diode, or a plurality of laser diodes configured in an array.
Further details are enclosed e.g. in U.S. Pat. No. 9,645,479 B2.
The light emitting element emits photoluminescent light by being excited with light emitted from the light source.
As discussed above, the present disclosure provides a projector device, comprising
(i) a light source apparatus according to the present disclosure,
(ii) a light modulation element, and
(iii) a projection optical system.
The light modulation element modulates light which is ejected from the light source apparatus. The projection optical system projects light from the light modulation element.
Further details are enclosed e.g. in U.S. Pat. No. 9,645,479 B2.
In one embodiment the projector device can be a projection type image display apparatus which projects a screen of a personal computer, a video footage, or the like on a screen.
As discussed above, the present disclosure provides a method of obtaining semiconductor nano(crystal) materials (NC) encapsulated in a shell, comprising the steps of
In one embodiment, the NC comprise elements of several groups of the periodic system, as defined herein,
and/or wherein the shell material is a non-emissive material as defined herein.
As discussed above, the present disclosure provides a method of obtaining emissive semiconductor nano(crystal) material(s) (NC) encapsulated in a monolith, comprising the steps of
In one embodiment, the NC comprise elements of several groups of the periodic system, as defined herein, and/or wherein the monolith material is a non-emissive material as defined herein.
In one embodiment, the methods further comprise the use of support ligands during the encapsulation, wherein
(i) the support ligands are directly ad-mixed to the encapsulation reaction mixture during the encapsulation process and allowed to react with the emissive semiconductor nano(crystal) material(s) typically before the shell or monolith formation; or
(ii) the support ligands are separately reacted with the initial NC material prior to the encapsulation, such that a protective ligand shell on the NC is formed which is not exchanged during the encapsulation process, i.e. during the shell or monolith formation.
In one embodiment, the support ligands comprise organic ligands and/or inorganic ligands as defined herein.
As discussed above, the present disclosure provides a method of generating a thin layer or film comprising emissive semiconductor nano(crystal) material(s), a binder material, and optionally other additives, which are deposited on a substrate.
In one embodiment, the substrate is a flat piece of glass, ceramic or metal material with reflective surface.
In one embodiment, the NC material is one of non-modified pristine NC nanocrystals, NC encapsulated in shell, and/or NC encapsulated in monolith.
In one embodiment, the binder material serves to hold the NC material and/or the other additives together, and at the same time ensures a good adhesion of the NC film to the substrate.
In one embodiment, the binder material(s) are as defined herein.
The light emitting element thin film characteristics are preferably:
The method of generating a thin layer or film comprises:
Binder curing is done by heat exposure (thermal curing), UV exposure (UV curing), and/or chemical curing.
In one embodiment, binder curing conditions for film preparation are between complete inert (0% oxygen, 0% relative humidity) to ambient (21% oxygen, up to 100% relative humidity); and/or temperature of binder curing is between ambient (22° C.) and 180° C.; and/or UV exposure for binder curing is between 1 J/cm2 and 16 kJ/cm2 preferably between 10 J/cm2 and 10 J/cm2.
As discussed above, the present disclosure provides a method of increasing the thermal conductivity of light emitting element, comprising
(i) mechanical ad-mixing of high thermal conductivity materials to the NC/binder system, preferably as obtained with the method of generating a thin layer or film (see above) the present disclosure,
or
(ii) co-incorporation of high-thermal conductivity materials and NC into the shell or monolith encapsulation matrix, preferably as obtained with one of the methods of the present disclosure.
The high-thermal conductivity materials preferably comprise:
inorganic oxide materials,
ceramic materials,
carbon-based materials,
Note that the present technology can also be configured as described below.
(1) A light emitting element
comprising emissive semiconductor nano(crystal) material(s) (NC).
(2) The light emitting element of embodiment (1), wherein the nano(crystal) material(s) (NC) are encapsulated in non-emissive material(s)
(a) in a shell, or
(b) in a monolith.
(3) The light emitting element of embodiment (1) or (2), wherein said emissive semiconductor NC comprise elements of several groups of the periodic system, such as but not limited to:
(i) type II/VI semiconductor materials,
(ii) type III/V semiconductor materials,
(iii) group IV-VI elements,
(iv) group IB-(III)-VI elements,
(v) group IV elements,
(vi) organometallic halide perovskites,
such as
(i) inorganic oxide or nitride materials,
such as
(ii) polymer-based composite materials,
such as
(i) inorganic oxide or nitride materials,
such as
(ii) polymer-based materials,
such as
(iii) single crystals,
such as
(i) organic ligands,
such as
(ii) inorganic ligands,
such as
inorganic oxide materials,
ceramic materials,
carbon-based materials,
silicone resin polymers
siloxane polymers,
thermoplastic polymers,
organic-inorganic silica polymers,
inorganic oxide materials,
inorganic polysilazanes,
ceramic materials,
composite materials,
inorganic oxide materials,
ceramic materials,
carbon-based materials,
(i) a light source, and
(ii) at least one light emitting element according to any one of embodiments (1) to (12), or a plurality of light emitting elements according to any one of embodiments (1) to (12).
(14) A projector device, comprising
(i) a light source apparatus according to embodiment (13),
(ii) a light modulation element, and
(iii) a projection optical system.
(15) A method of obtaining emissive semiconductor nano(crystal) material(s) (NC) encapsulated in a shell, comprising the steps of
providing NC material(s),
providing chemical precursors for the synthesis of the monolith,
carrying out a chemical reaction to form the monolith encapsulation of NC,
isolating the monolith encapsulated NC material,
wherein the NC comprise elements of several groups of the periodic system, as defined in embodiment (3),
and/or wherein the monolith material is a non-emissive material as defined in embodiment (6).
(17) The method of embodiment (15) or (16), comprising the use of support ligands during the encapsulation, wherein
(i) the support ligands are directly ad-mixed to the encapsulation reaction mixture during the encapsulation process and allowed to react with the NC nanocrystals typically before the shell or monolith formation; or
(ii) the support ligands are separately reacted with the initial NC material prior to the encapsulation, such that a protective ligand shell on the NC is formed which is not exchanged during the encapsulation process, i.e. during the shell or monolith formation,
and wherein the support ligands comprise organic ligands and/or inorganic ligands as defined in embodiment (7).
(18) A method of generating a thin layer or film comprising semiconductor nano(crystal) materials, a binder material, and optionally other additives, which are deposited on a substrate,
said method comprising the steps of
(i) mechanical ad-mixing of high thermal conductivity materials to the NC/binder layer, preferably as obtained with the method of embodiment (18),
or
(ii) co-incorporation of high-thermal conductivity materials and NC into the shell or monolith encapsulation matrix, preferably as obtained with a method of any one of embodiments (15) to (17),
wherein the high-thermal conductivity material(s) preferably comprise:
The term “semiconductor nano(crystal) material (NC)”, as used herein, refers semiconductor nanocrystals which can emit pure monochromatic red, green, and blue light.
The term “shell”, as used herein, refers to a spatially discrete object in which preferably single NC particles are embedded; the shape of the shell could be spherical, spheroid, rod-like, disk-like, and platelet-like.
The term “monolith”, as used herein, refers to a matrix which is not spherical and is not a bead. A monolith is a semi-dimensional structure which could be described as a flake. A “monolith” is understood as a spatially discrete microscopic object with homogeneous microstructure in which multiple NC particles are embedded; monolith object is characterized by its irregular shape, e.g. flake-like, platelet-like, needle-like, grain-like. Single NC particles within the monolith are separated by thin layers of material from the monolith matrix. Size of the microscopic monolith objects can be between 0.2 μm and 1000 μm, preferably between 1 μm and 20 μm.
The present invention relates to semiconductor nano(crystal) material(s) emissive materials as light emitting material implemented in a solid state projector light source with the purpose to improve the stability, the quantum efficiency, the spectral properties and the colour rendering capabilities.
Furthermore, the present invention is related to a projector light source using such emissive materials.
The present disclosure provides the following features:
The present disclosure provides:
Examples for Photostability Improvement Through Encapsulation of QD:
Improvement of photostability of Cd-based NC through encapsulation is demonstrated by the following examples (Table 1).
The photostability of the NC material was assessed as the loss of photoluminescence intensity after 24 h excitation with continuous wave laser diode (LD) array, using excitation wavelength 450 nm.
| Number | Date | Country | Kind |
|---|---|---|---|
| 19176156.8 | May 2019 | EP | regional |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2020/056973 | 3/13/2020 | WO | 00 |
