Patent Application
20070262294
In spectroscopy or color measurement applications which characterize the transmission, absorption, emission or reflection of a target material (such as ink on paper, paint on metal, dyes on cloth, etc.), an illumination source must be present, as well as an apparatus to measure the reflected, transmitted or emitted light. One method for providing the illumination is using light emitted from light emitting diodes (LEDs). To adequately characterize the material properties of the target that would be seen by a human observer, illumination over the entire visible wavelength range from 400 nm to 700 nm is desirable. Individual white or chromatic LEDs and even multiple-LED assemblies, however, often do not provide adequate intensity at all wavelengths in this range.
One known solution for tailoring the emission spectra of a LED to cover the desired illumination range is to use an interference filter with the LED to filter out the unwanted wavelengths. Such an arrangement, however, is not practical where the source (e.g., the LED) does not emit sufficient energy at the desired wavelength. Also, such arrangements can be inefficient for certain applications because much of the energy emissions from the source may be filter out and therefore wasted.
In one general aspect, the present invention is directed to a light source comprising a light emitting device and quantum dot material. The quantum dot material is positioned relative to the light emitting device such that the quantum dot material absorbs light emitted from the light emitting device and converts the wavelengths of at least a portion of the photons emitted from the light emitting device to longer wavelengths. Judicious selection of the quantum dot material allows the emission spectra of the light source to be tailored to meet the needs of a particular illumination application, and avoids the drawbacks associated with the use of interference filters because the quantum dot material can upconvert the wavelengths emitted from the light emitting device such that the emission spectra of the light source can include wavelengths that are not emitted by the light emitting device itself.
According to various implementations, the quantum dot material may comprise a host material and a plurality of quantum dot material intra-layers suspended in the host material, wherein the quantum dot material intra-layers have different light absorption/emission characteristics. Also, the quantum dot material may be positioned directly on the light emitting device, or it may be a part of a quantum dot material assembly spaced apart from the light emitting device that comprises (1) an optically transparent substrate and (2) one or more quantum dot material layers. The quantum dot material layer(s) may comprise quantum dot material and the host material, and the assembly is positioned such that light from the light emitting device is absorbed by the quantum dot material layer(s) on the substrate.
In addition, the light emitting device may comprise one or a number of light emitting diodes (LEDs), one or a number of lasers, one or a number of laser diodes, a lamp, or a combination of these light emitting devices.
The quantum dot material may be chosen such that the emission spectra of the light source meets a desired emission spectra profile. For example, the emission spectra profile may correspond to an adopted industry illumination standard, such as an incandescent illumination standard, a daylight illumination standard or a fluorescent illumination standard. Also, the quantum dot material may be chosen such that the emission spectra of the light source may cover a narrow band of wavelengths, for example.
In addition, the light source may comprise (1) a lower lens between the light emitting device and the quantum dot material for collecting and focusing light from the light emitting device onto the quantum dot material and/or (2) an upper lens, wherein the quantum dot material is between the light emitting device and the upper lens, for collecting and focusing light from the quantum dot material on a target sample material.
In another general aspect, the present invention is directed to an apparatus for measuring a spectroscopic property of a target material. The apparatus may comprise, for example, the above-described light source for emitting light photons to impinge upon the target material and an optical radiation sensing device for detecting light reflected by the target material. The apparatus may, of course, comprise other components.
Various embodiments of the present invention are described herein by way of example in conjunction with the following figures, wherein:
The light source 10 illustrated in
In the light source 10 of
According to various embodiments, the quantum dot material layer 20 may comprise a composite of different quantum dot intra-layers 21a-c suspended in the host material 23, as shown in
The substrate 22 on which the quantum dot material layer 20 is placed may be optically transparent such that all or most of the light from light emitting device 12 passes through the substrate 22 and impinges on the quantum dot material layer 20. According to various embodiments, the substrate 20 may be made from glass, such as sapphire glass. The substrate 22 may be spaced-apart from the light emitting device 12 as shown in
According to various embodiments, the light source 10 may comprise multiple quantum dot assemblies 18.
In other embodiments, rather than using two (or more) substrates 22a,b as in the embodiment of
According to other embodiments, as shown in
In other embodiments, as shown in
By careful selection of various options, including the characteristics of the quantum dot material layer(s) 20 (including the number and characteristics of the intra-layers 21, if any), the number of quantum dot material layers 20, and the light emission spectral characteristics of the light emitting device 12, a desired emission spectra profile may be produced (or at least approximated). For example, in one embodiment, the light emitting device 12 may emit photons in the ultraviolet portion of the optical spectrum (wavelengths <400 μm), and the quantum dot material assembly 18 may convert the pump light to greater wavelengths at sufficient intensities over a broad spectrum, such as wavelengths of 400 nm to 700 nm. According to another embodiment, the light emitting device 12 may emit photons in the blue portion of the optical spectrum (wavelengths between 400 nm and 425 nm), and the quantum dot material assembly 18 may emit light at sufficient intensities over the 400 nm to 700 nm range.
According to other embodiments, the quantum dot material layer(s) 20 may be chosen such that the emission spectra of the light source 10 is limited to a narrow band of wavelengths. As used herein, “narrow band” means less than or equal to 50 nm full width at half maximum (FWHM). That is, when the emission spectra of the light source 10 is a narrow band, the difference between the wavelengths at which emission intensity of the light source is half the maximum intensity is less than or equal to 50 nm.
According to other embodiments, the quantum dot material layer(s) 20 may be chosen such that the emission spectra of the light source corresponds to a known spectral emission standard such as, for example, incandescent standards (e.g., CIE standard illuminant A), daylight standards (e.g., CIE standard illuminant D65 or D50), fluorescent standards (e.g., CIE standard illuminant F2 or F11), or other defined standards.
One or more of the light sources 10 described above may be employed, for example, in a color measurement or spectroscopic apparatus to measure the transmission, absorption, emission and/or reflection properties of a material.
One or more of the light sources 10 could be used in other equipment, including, for example, a printing press, an ink jet printer, or other color-based process monitoring equipment.
While several embodiments of the invention have been described, it should be apparent, that various modifications, alterations and adaptations to those embodiments may occur to persons skilled in the art with the attainment of some or all of the advantages of the invention. For example, the materials and the emission spectra profiles described herein are illustrative only. All such modifications, alterations and adaptations are intended to be covered as defined by the appended claims without departing from the scope and spirit of the present invention.
