Organic molecules with delayed fluorescence applied to human-centric lighting and radiation detectors

Abstract

An exemplary embodiment of the present disclosure provides a spectrally tunable light source, comprising a plurality of light converters and a controller. Each light converter can comprise a thermal activated delay fluorescence (TADF) material and a light source. The light source can be configured to direct light on the TADF material. The TADF material can be configured to emit light having a predetermined range of wavelengths in response to light from the light source. The controller can be configured to control the light source of each of the plurality of light converters to alter a light output of the plurality of light converters.

Description

ORGANIC MOLECULES WITH DELAYED FLUORESCENCE APPLIED TO HUMAN-CENTRIC LIGHTING AND RADIATION DETECTORS CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit of U.S. Provisional Application Serial No. 63 / 559,669, filed on 29 February 2024, which is incorporated herein by reference in its entirety as if fully set forth below. GOVERNMENT LICENSE RIGHTS

[0002] This invention was made with government support under DE-EE0008205 awarded by the U.S. Department of Energy, and DE-NA0003921 awarded by the National Nuclear Security Administration. The government has certain rights in the invention. FIELD OF THE DISCLOSURE

[0003] The various embodiments of the present disclosure relate generally to systems and methods for generating light. BACKGROUND

[0004] Light is vital to human life. Artificial lighting has evolved over thousands of years from using candlelight, to electric incandescent light sources over the last century, and most recently, ushering in the LED revolution of the past 30 years, driven by the aspect of sustainability pertaining to energy efficiency as well as increased awareness over the physiological and / or psychological effect upon humans.

[0005] Although natural daylight is essential for optimal health, Americans spend over 90% of their entire lives indoors according to the Environmental Protection Agency, a figure even higher for countries with harsh climate. It is not always feasible to provide outdoor exposure to all building occupants across varying climates, nor daylighting in energy efficient buildings due to heating and glare considerations.

[0006] Throughout the day, daylight’s evolving spectral power distribution (SPD) provides cues that regulate vital neurobiological functions, by way of the light incident on the back of the eye. These effects go beyond the visual perception of color, based on light reflected by surfaces and objects, which can induce fatigue and eye strain. Health effects from circadian health disruption include metabolic, endocrine, and circadian cycle regulation, leading toaffected mood, alertness, cancer rates. Therefore, a human-centric lighting solution would desirably possess high fidelity of both visual and circadian effects with respect to natural light.

[0007] Despite progress in color-tunable technologies to date, no lighting technology can replicate all of the characteristics of daylight, such as illuminance values exceeding 100,000 lx. For this study, the scope is limited only to reproducing the lighting performance metrics corresponding to the SPD of natural light, over the range of visible wavelengths at a luminance relevant to indoor daytime lighting, i.e. 250 photopic lux. Furthermore, achieving high performance as measured by standard metrics used in evaluating artificial lighting, such as the correlated color temperature (CCT) and color rendering index (CRI), is insufficient to develop artificial lighting that approximates the characteristics of natural daylight. State-of-the-art color mixed LEDs (cm-LED) can be electronically controlled to match the color coordinates for a given CCT, but differ significantly in circadian lighting and color rendering.

[0008] For instance, when an amber-emitting phosphor-converted LED (pc-LED) channel is added to a 3-channel cm-LED, producing an RGBA (red, green, blue, alpha) LED, circadian lighting match to an incandescent 2700 K SPD is improved to suitable levels for minimizing light pollution and circadian disruption, but color rendering at CCT of 6504 K remains low with IES (Illuminating Engineering Society) color fidelity index Rf values near 70. Even when a fifth LED channel is added, the CRI remains under 90, and the energy related to circadian lighting exceeds that of daylight with CCT of 6504 K by over 10%, at the same luminance and CCT. Linear combination of pc-LED channels can achieve tunable circadian lighting, such as the product named BIOS, but their CCT can only be tuned between 2700 K and 3500 K, with a reported CRI of 80 for the 3500 K condition. Other pc-LEDs can approximate sunlight with various CCT by employing around 12 phosphors, accurately reproducing color rendering and circadian lighting performance, but the CCT value of the LED chip is fixed at manufacturing time, prohibiting SPD tunability during operation. Similarly, LEDs using Cu(I) halides conversion layers reach CRI values ranging from 62.3 to 73.9 but lack SPD tunability. Hybrid organic / inorganic LEDs employing III-V blue LEDs with organic light converters can achieve very high CRI values of 95.7, but lack SPD tunability. On the other hand, white organic light- emitting diodes (WOLED) show advantages in reduction of blue light at night and a diffuse light distribution, but their tandem layer stack architecture prevents SPD tunability.

[0009] The cool white WOLED option’s SPD reaches a melanopic equivalent daylight illuminance (melanopic EDI) that is 68% of that of daylight with a CCT value of 6,504 K, at the same luminance of 250 photopic lux. These limitations for WLED and WOLEDtechnologies in enabling human-centric lighting, are intrinsic to the photophysics of their materials and device architectures.

[0010] Accordingly, there is a need for improved systems and methods for delivering human- centric lighting. The present disclosure provides such systems and methods. BRIEF SUMMARY

[0011] An exemplary embodiment of the present disclosure provides a spectrally tunable light source, comprising a plurality of light converters and a controller. Each light converter can comprise a thermal activated delay fluorescence (TADF) material and a light source. The light source can be configured to direct light on the TADF material. The TADF material can be configured to emit light having a predetermined range of wavelengths in response to light from the light source. The controller can be configured to control the light source of each of the plurality of light converters to alter a light output of the plurality of light converters.

[0012] In any of the embodiments disclosed herein, the plurality of light converters can comprise a first light converter configured to emit light having a first predetermined range of wavelengths and a second light converter configured to emit light having a second predetermined range of wavelengths.

[0013] In any of the embodiments disclosed herein, the first light converter can comprise a first TADF material, and the second light converter can comprise a second TADF material.

[0014] In any of the embodiments disclosed herein, the light source of each of the plurality of light converters can comprise a light emitting diode.

[0015] In any of the embodiments disclosed herein, the light emitting diode can be configured to emit light having a wavelength of 380 nm to 750 nm.

[0016] In any of the embodiments disclosed herein, the controller can be configured to control the light source of each of the plurality of light converters to alter a wavelength of light output of the plurality of light converters.

[0017] In any of the embodiments disclosed herein, the controller can be configured to control the light source of each of the plurality of light converters to alter an intensity of light output by the plurality of light converters.

[0018] In any of the embodiments disclosed herein, the controller can be configured to control whether each light source of the plurality of light converters is on or off.

[0019] In any of the embodiments disclosed herein, the controller can be configured to control an intensity of light emitted by each light source of the plurality of light converters.

[0020] In any of the embodiments disclosed herein, a first portion of the plurality of light converters can be configured to emit light having a first range of wavelengths, and a second portion of the plurality of light channels can be configured to emit light having a second range of wavelengths.

[0021] Another embodiment of the present disclosure provides a spectrally tunable light source, comprising a first light converter, a second light converter, and a controller. The first light converter can comprise a first emitter comprising a first TADF material and a first light source configured to illuminate the first emitter. The first emitter can be configured to emit light having a first range of wavelengths in response to illumination by the first light source. The second light converter can comprise a second emitter comprising a second TADF material and a second light source configured to illuminate the second emitter. The second emitter can be configured to emit light having a second range of wavelengths in response to illumination by the second light source. The controller can beconfigured to control an output of the first and second light sources to alter a light output by the spectrally tunable light source.

[0022] In any of the embodiments disclosed herein, the spectrally tunable light source can further comprise a third light converter and a fourth light converter. The third light converter can comprise a third emitter comprising the first TADF material and a third light source configured to illuminate the third emitter. The third emitter can be configured to emit light having the first range of wavelengths in response to illumination by the third light source. The fourth light converter can comprise a fourth emitter comprising the second TADF material and a fourth light source configured to illuminate the fourth emitter. The fourth emitter can be configured to emit light having the second range of wavelengths in response to illumination by the fourth light source. The controller can be further configured to control an output of the third and fourth light sources to alter a light output by the spectrally tunable light source.

[0023] Another embodiment of the present disclosure provides a method of emitting light, comprising: providing a plurality of light converters, each light converter comprising a thermal activated delay fluorescence (TADF) material and a light source configured to direct light on the TADF material, wherein the TADF material is configured to emit light having a predetermined range of wavelengths in response to light from the light source; and controlling the light source of each of the plurality of light converters to alter a light output of the plurality of light converters.

[0024] In any of the embodiments disclosed herein, controlling the light source of each of the plurality of light converters can alter a wavelength of light output by the plurality of light converters.

[0025] In any of the embodiments disclosed herein, controlling the light source of each of the plurality of light converters can comprise controlling whether each light source of the plurality of light converters is on or off.

[0026] In any of the embodiments disclosed herein, controlling the light source of each of the plurality of light converters can alter an intensity of light emitted by each light source of the plurality of light converters.

[0027] These and other aspects of the present disclosure are described in the Detailed Description below and the accompanying drawings. Other aspects and features of embodiments will become apparent to those of ordinary skill in the art upon reviewing the following description of specific, exemplary embodiments in concert with the drawings. While features of the present disclosure may be discussed relative to certain embodiments and figures, all embodiments of the present disclosure can include one or more of the features discussed herein. Further, while one or more embodiments may be discussed as having certain advantageous features, one or more of such features may also be used with the various embodiments discussed herein. In similar fashion, while exemplary embodiments may be discussed below as device, system, or method embodiments, it is to be understood that such exemplary embodiments can be implemented in various devices, systems, and methods of the present disclosure. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] The following detailed description of specific embodiments of the disclosure will be better understood when read in conjunction with the appended drawings. For the purpose of illustrating the disclosure, specific embodiments are shown in the drawings. It should be understood, however, that the disclosure is not limited to the precise arrangements and instrumentalities of the embodiments shown in the drawings.

[0029] FIG.1 provides a schematic diagram of a spectrally tunable light source, in accordance with an exemplary embodiment of the present disclosure.

[0030] FIG. 2 provides a schematic of a light converter, in accordance with an exemplary embodiment of the present disclosure.

[0031] FIG.3 provides plots of photoluminescence (PL) spectrum of TADF light-converters including electroluminescent (EL) spectrum of 415 nm VLED with accompanying photographs of devices under 415 nm VLED illumination, in accordance with an exemplary embodiment of the present disclosure.

[0032] FIGs. 4A-H provide SPD of illuminance scaled to 250 photopic lux for TADF- WLED and RGBA LED with reference SPD at same photopic lux used for evaluation of performance metrics, with (4A) incandescent SPD with CCT of 2855 K and (4B) daylight SPD with CCT 6504 K, and bar graphs of results of benchmark for (4C) and (4D) s-opic EDI Efficiency and melanopic EDI Efficiency; (4E) and (4F) color rendering performance metrics compared; and (4G) and (4H) CS Efficiency, CLAEfficiency, and EML Efficiency benchmarked to reference SPDs of incandescent 2855 K (4C), (4E), and (4G) and daylight 6504 K (4D), (4F), and (4H), with target value of figure of merit 100 denoted by horizontal lines.

[0033] FIGs. 5A-D provide plots showing (5A) SPD variations for TADF-WLED and (5B) for cm-LED, with insets showing standard deviation of variation per channel optical power<>LIMM <FF ,( P<LD<HN 973M$ <H? ",2# =IR%<H?%QCDME@L ?<N< AIL @<>C IA NC@ V%IJD> 435Efficiencies with corresponding standard deviation for TADF-WLED and (5D) box-and-QCDME@L ?<N< AIL @<>C IA NC@ V%IJD> 4354AAD>D@H>D@M QDNC >ILL@MJIH?DHB MN<H?<L? ?@PD<NDIH AILcm-LED.

[0034] FIGs.6A-C provide plots showing performance metrics of TADF-WLED compared to reference spectra of daylight in early morning (CCT 5002 K), mid-morning (CCT 5499 K),IP@L><MN ?<SNDG@ "22: .,(.6#$ <H? MOHM@N MESFDBCN "22: +*..6# DH>FO?DHB "-1# V%IJD> 435Efficiency, (6B) color rendering and (6C) CS Efficiency, CLAEfficiency, and EML Efficiency. DETAILED DESCRIPTION

[0035] Although preferred exemplary embodiments of the disclosure are explained in detail, it is to be understood that other exemplary embodiments are contemplated. Accordingly, it is not intended that the disclosure is limited in its scope to the details of construction and arrangement of components set forth in the following description or illustrated in the drawings. The disclosure is capable of other exemplary embodiments and of being practiced or carried out in various ways. Also, in describing the preferred exemplary embodiments, specific terminology will be resorted to for the sake of clarity.

[0036] To facilitate an understanding of the principles and features of the present disclosure, various illustrative embodiments are explained below. The components, steps, and materials described hereinafter as making up various elements of the embodiments disclosed herein are intended to be illustrative and not restrictive. Many suitable components, steps, and materials that would perform the same or similar functions as the components, steps, and materials described herein are intended to be embraced within the scope of the disclosure. Such other components, steps, and materials not described herein can include, but are not limited to, similar components or steps that are developed after development of the embodiments disclosed herein.

[0037] As used in the specification and the appended claims, the singular forms “a,” “an” and “the” include plural referents unless the context clearly dictates otherwise.

[0038] Also, in describing the preferred exemplary embodiments, terminology will be resorted to for the sake of clarity. It is intended that each term contemplates its broadest meaning as understood by those skilled in the art and includes all technical equivalents which operate in a similar manner to accomplish a similar purpose.

[0039] Ranges can be expressed herein as from “about” or “approximately” one particular value and / or to “about” or “approximately” another particular value. When such a range is expressed, another exemplary embodiment includes from the one particular value and / or to the other particular value.

[0040] Similarly, as used herein, “substantially free” of something, or “substantially pure”, and like characterizations, can include both being “at least substantially free” of something, or “at least substantially pure”, and being “completely free” of something, or “completely pure”.

[0041] By “comprising” or “containing” or “including” is meant that at least the named compound, member, particle, or method step is present in the composition or article or method, but does not exclude the presence of other compounds, materials, particles, method steps, even if the other such compounds, material, particles, method steps have the same function as what is named.

[0042] Mention of one or more method steps does not preclude the presence of additional method steps or intervening method steps between those steps expressly identified. Similarly, it is also to be understood that the mention of one or more components in a device or system does not preclude the presence of additional components or intervening components between those components expressly identified.

[0043] The materials described as making up the various members of the invention are intended to be illustrative and not restrictive. Many suitable materials that would perform the same or a similar function as the materials described herein are intended to be embraced within the scope of the invention. Such other materials not described herein can include, but are not limited to, for example, materials that are developed after the time of the development of the invention.

[0044] Reference will now be made in detail to exemplary embodiments of the disclosed technology, examples of which are illustrated in the accompanying drawings and disclosed herein. Wherever convenient, the same references numbers will be used throughout the drawings to refer to the same or like parts.

[0045] As shown in FIG. 1, an exemplary embodiment of the present disclosure provides a spectrally tunable light source 100. The light source 100 can comprise a plurality of light converters 105A-D and a controller 110. The present disclosure is not limited to any particular number of light converters and should be construed as including many different numbers of light converters. As shown in FIG.3, each light converter 105 can comprise a thermal activated delay fluorescence (TADF) material 107. The TADF material 107 can be many different TADF materials, including, but not limited to TXO-TPA, TCZPBOX, 4CzIPN, 2CzPN, oBFCzTrz, TXO-PhCz, DMTDAc, tBuCzDBA, and the like.

[0046] Each light converter can further comprise a light source 106. The light source 106 can be many different light sources. In some embodiments, the light source 106 can comprise a light emitting diode (LED). The LEDs can be many different LEDs known in the art, including, but not limited to VLEDs, OLEDs, and the like. The LED light source can be configured to emit a wavelength of light between 300 nm and 450 nm.

[0047] The light source 106 can be configured to direct light on the TADF material 107. For example, in some embodiments, as shown in FIG. 3, the light source 106 can be positioned beneath the TADF material 107. In response to light stimulation by the light source 106, the TADF material 107 can be configured to fluoresce, emitting light having a predetermined range of wavelengths. The predetermined range of wavelengths can correspond to the particular TADF material selected.

[0048] The controller 110 can be configured to control the light source of each of the plurality of light converters to alter a light output of the plurality of light converters. The controller 110 can be many controllers known in the art and comprise a combination of hardware and software to control the light sources 106 of each of the light converters. In some embodiments, thecontroller 110 can comprise a plurality of subcontrollers, wherein each subcontroller is configured to control one (or a subset) of the plurality of light converters 105A-D. For example, the controller 110 can be configured to individually turn the light sources 106 of the light converters 105A-D on and off and / or to individually adjust an intensity of each of the light sources 106.

[0049] In some embodiments, the plurality of light converters 105A-D can comprise a first light converter 105A (or first subset of light converters) configured to emit light having a first predetermined range of wavelengths and a second light converter 105B (or second subset of light converters) configured to emit light having a second predetermined range of wavelengths. In some embodiments, the plurality of light converters could similarly comprise third 105C (or third subset) or more light converters. In such embodiments, the first light converter 105A (or first subset of light converters) can comprise a first TADF material, and the second light converter 105B (or second subset of light converters) can comprise a different second TADF material. The wavelength of light emitted by the light converters 105A-D can correspond to the TADF material 107 of the converter.

[0050] When the light converters 105A-D emit different wavelengths of light, the controller 110 can control the various converters to control characteristics of the composite light emitted by the spectrally tunable light source 100. For example, by controlling which light sources 106 of the light converters 105A-D are on / off and / or the intensity of each, the controller 110 can be used to alter a wavelength (or range of wavelengths) and / or intensity of the composite light emitted by the spectrally tunable light source 100. Thus, by specific selection of TADF materials and control of each light converter 105A-D, a spectrally tunable light source 100 is provided, which can, for example, mimic human-centric lighting conditions. EXAMPLES

[0051] Below certain exemplary embodiments of the light sources of the present disclosure and their operation are discussed. These examples, however, are for illustration purposes only and should not be construed to limit the scope of the present disclosure.

[0052] Disclosed below are exemplary novel electronically spectrally-tunable hybrid organic / inorganic light sources, comprising a combination of spectra emitted by light converter channels based on thermally-activated delayed fluorescence (TADF) dyes photoexcited by violet-emitting LEDs (VLED). Furthermore, these light converters can be fabricated through additive manufacturing to enable ease of integration. Herein, these light sources are sometimes referred to as a TADF-WLED, shown in FIG. 1. TADF-WLEDdiffers, at least in part, from state-of-the-art color-tunable WLEDs in that they allowapproximating targeted 0",-*' %$& where 0 # ., m, l, indexes corresponding to short (s),medium (m), and long (l) wavelength receptors, and 0 can also refer to the melanopsin-containing or rhodopsin receptors in the human eye, relevant to color rendering and circadian lighting performance.

[0053] This linear combination is mathematically described in Eq. (1) below with device compositions found in the “Methods” section below, Table 1. Eq. 1: SPDWLED = C1SPDLED,1 + C2SPDLED,2 + ... + CNSPDLED,N

[0054] In some embodiments of the TADF-WLED, all current can be injected into VLED with a peak wavelength of 415 nm, exploiting the higher wall-plug efficiency of VLED compared to green- and amber-emitting LEDs, lower by 53.9% and 85.5% respectively, serving as a proof of concept establishing a roadmap towards high efficiency lighting systems surpassing 390 lm / W based on the high Stokes Shift that is characteristic of TADF emitters compared to traditional fluorescent and phosphorescent emitters, with high color-rendering and circadian lighting performance. This addresses the current tradeoff between color rendering and energy efficiency.

[0055] The TADF molecules were chosen due to their potential of achieving high photoluminescence efficiency, reduced dimerization favorable for photostability, and because their inherent disorder and 3D molecular shapes can result in broad spectral emission compared to fluorescent emitters, which is favorable for solid-state lighting. Additionally, both TADF molecules and stereolithography are reputed to be low-cost methods due to decreased complexity in processing and low cost of raw materials. The reason for the spectrally broad emission can be attributed to the charge-transfer characteristic of the lowest energy excited state.

[0056] TADF-WLED can achieve an SPD approximating that of daylight as described by CIE Standard Illuminant D, with CCT ranging from 4277 K to 22,333 K, corresponding to sunlight at different times of the day, varying climates, and weather conditions such as clear morning, mid-day, sunset, overcast daylight, and the northern sky. In addition, the TADF- WLED provides an approximation comparable to the state-of-the-art color tunable LEDs to an incandescent light source as described by CIE Standard Illuminant A, an illuminant of interest towards reducing sky glow, light pollution, and disruption of nocturnal ecosystems. No other color-tunable LED technology achieves this function. All reference SPDs were scaled to a luminance value of 250 photopic lux.

[0057] The degree to which an LED’s SPD delivers energy to each relevant photoreceptor in the eye can be quantified by metrics introduced over the last decade by the CIE, such as 0" opic EDI in units of (cdmU )defined in CIE Standard S 026. However, for benchmarking purposes to compare different light sources, a new figure of merit is introduced that describesthe 0",-*' %$& %))*'*(+' / in units of (%), or how closely the EDI of the light source underevaluation approximates that of the relevant reference illuminant, given the same illuminanceof X photopic lux (defined in Eq. 2 below).4K& * / V IJD> 4354AAD>D@H>S 0"V IJD> 435 "973##'" V IJD> 435"8@A& 5FFOGDH<HN##T ; JCINIJD> FOR

[0058] These metrics can be computed for each photoreceptor within the human eye relevant to the application in order to validate that these metrics capture visual and circadian characteristics of lighting. Color rendering was characterized using IES Standard TM-30-15, which measures both color fidelity index Rfand color gamut index Rg, to describe how a light source renders the hue of objects, as well as the shift in hue with respect to reference light source, evaluated over 99 color samples representing many objects. The color fidelity index, Rf, describes how accurately the hue of color will be reproduced similar to CRI but covering a larger color sample pallet, and the color gamut index Rgdescribes how saturated or de- saturated the colors appear with respect to the reference illuminant. CRI, or CIE General Color Rending Index is denoted by Ra, but priority is given to Rfand Rgmetrics, as CRI is limited to a single value for fidelity and uses only eight color samples that are less representative of the infinite color possibilities encountered by users. No further processing was performed on Rfand Rgas they are already a ratio between the light source in evaluation and the reference illuminant. Values of Rf and Rg can exceed 100, but this may not be desirable in this application, since it translates to higher-than-natural color hue distortion orsaturation. The high values in Rfseen with the TADF-WLED translate to high CRI values, so the same conclusions can be drawn from both values.

[0059] Circadian lighting performance was characterized through a figure of merit based on circadian stimulus (CS), circadian lighting (CLA), and equivalent melanopic lux (EML). These metrics are defined based on standards1,4,35 that account for sensitivity of melanopsin photopigment contained within the ipRGC, and CS and CLA take into account the effect of the transduction of light through the front of the eye. To better enable benchmarking how closely the light source approximates the corresponding reference illuminant, a set of figures of merit can be defined describing as CS Efficiency, CLAEfficiency, and EML Efficiency given by Eqs. (3)–(5). Eq. 3: CS Efficiency = (CS (SPD)) / (CS (Ref. Illuminant))|(X photopic lux) Eq. 4: CLA Efficiency = (CLA (SPD)) / (CLA (Ref. Illuminant))|(X photopic lux) Eq. 5: EML Efficiency = (EML (SPD)) / (EML (Ref. Illuminant))|(X photopic lux)

[0060] The TADF light converters were fabricated individually as shown in “Methods” section, “Materials” and “Fabrication” subsections, and the linear combination of the channel SPDs was achieved in practice by an embedded computing platform built in-house, utilizing open-source hardware and software. The SPD tuning was achieved by manually tuning the currents in MATLAB for simulated SPDs with luminance scaled to 250 photopic lux.

[0061] Results and discussion Comparison to tunable LED

[0062] For benchmarking to quantify the performance of TADF-WLED, the SPD of the TADF-WLED was first compared to the SPD of an RGBA LED as found by the IES-TM-13 Color Rendering Toolbox. The SPDs were compared under low and a high CCT conditions, with the reference spectra of an incandescent bulb and daylight with a CCT of 6504 K respectively. The SPDs were equalized to a luminance of 250 photopic lux using MATLAB, representative of office lighting conditions. Rhodopsin sensitivity was excluded because it corresponds to vision in low-light conditions under 1 lx. The results of this benchmark are found in FIGs. 4A-H.

[0063] Bar graphs of the s-opic EDI Efficiency and melanopic EDI Efficiency were the focus of this analysis as m-opic Efficiency and l-opic EDI Efficiency were comparable since they contribute spectrally primarily to photopic vision, and luminance was fixed. For the incandescent SPD, the results show that the TADF-WLED s-opic EDI Efficiency is near 100% while for RGBA it is around 38%. In consequence, both Rf and Rg show a gain of nearly 20% for the TADF-WLED. Both have comparable CS Efficiency and CLAEfficiency,showing that no undesirable energy content is being introduced that can exacerbate melatonin suppression for nighttime use. For daylight at CCT of 6504 K, there are also comparable gains in color rendering. Melanopic EDI Efficiency is improved by over 20%, improving CS Efficiency and CLAEfficiency by 5% and 10% respectively, which is correlated to melatonin suppression potential.

[0064] &2'(-.-230+ 2,* 4"01-) $#% *++-)-* / )3

[0065] The next benchmark that was performed was the stability of the 0",-*' %$& %))*'*(+' / .For this benchmark, strictly III-V LED channels were used for the cm-LED as they are the long-term strategy for efficient color-tunable LED technology. This analysis is shown in FIGs. 5A-D. Fifty sampled SPD variants were synthesized numerically in MATLAB by varying the optical power of each channel within a tolerance of 10%. The TADF-WLED had comparable standard deviation in the m-opic EDI Efficiency, l-opic EDI Efficiency, and melanopic EDI Efficiency, while retaining more stability in the s-opic EDI Efficiency, with a standard deviation of melanopic EDI Efficiency, or 1mel of 3.8 compared to 6.1 for cm-LED. This is likely the byproduct of operating the blue III-V LED at a higher optical power to supply the correct amount of energy for s-cone photoreceptor, a design choice used to overcome the small FWHM of the emission spectrum of the LED.

[0066] Overall, the 0",-*' %$& %))*'*(+' / is slightly more robust to variations in the opticalpower of the TADF-WLED channels as shown in FIGs.5A-D. This is relevant because during operation, differential efficiency droops of the component III-V LEDs, differential aging, and LED driver variations all create a challenge for controls, posing a roadblock to adoption of network connected lighting systems.

[0067] This analysis was performed on III-V semiconductor five channel component cm-LED. While the devices resulted in improved performance 0",-*' %$& %))*'*(+' / metrics,color rendering showed limitations, with Rfvalues of 86, Rgof 106, and CRI of 83.9. Thesevalues were achieved in spite of excellent values for distance to black-body locus Duv = U + ×104and CCT matching reference daylight spectrum of 6504 K, metrics often used for simplicity due to correlation to the visual color appearance of a light source and its proximity to the color appearance of the reference black-body radiator.

[0068] Comparison to illuminants representing natural light

[0069] For the final benchmark, the TADF-WLED was compared to a set of illuminants representing natural light. These included measured sun and skylight SPD at sunset with CCT of 4277 K and Illuminant D with CCTs of 5002 K (horizon daylight), 5499 K (mid-morning daylight), 7005 K, and 7507 K (overcast daylight). The SPD of the northern sky was included because it may be of importance to inhabitants of the northern hemisphere. Illuminant A and the black-body spectrum with temperature of 3500 K were chosen because these spectra can be useful for minimizing melatonin suppression, light pollution for coastal ecosystems and migratory birds, and astronomical observatories.

[0070] The SPDs attained by the TADF-WLED utilized the same four light conversion layersand varied only the optical power output by each channel. FIGs. 6A-C show the 0",-*' %$&Efficiency, color rendering, and CS Efficiency, CLAEfficiency, and EML Efficiency metrics for TADF-WLED approximating the performance of a subset of the illuminants, specifically the early morning (5002 K), mid-morning (5499 K), overcast (7507 K), and sunset (4277 K), illustrating that no value has below a 95% match for these diverse set of conditions, with many of the 0-opic EDI Efficiency values staying within ± 3%, and Rg is 100 for three of the four conditions. This analysis also shows that the EML Efficiency mirrors the melanopic EDI Efficiency, consistent with the definitions based solely on corresponding sensitivity curve.

[0071] Methods

[0072] Materials

[0073] Synthesis of 5,5’-(2,3,5,6-tetra(9 H-carbazol-9-yl)-1,4-phenylene)bis(2-(4-(tert-butyl)phenyl)-1,3,4-oxadiazole), or TCZPBOX, was discussed in Zhang, X. et al.Host-free yellow-green organic light-emitting diodes with external quantum efficiency over 20% based on a compound exhibiting thermally activated delayed fluorescence. ACS Appl.Mater. Interfaces. 11, 12693–12698. https: / / doi.org / 10.1 021 / acsami.8b18798 (2019).Synthesis of 5-(2-(4,6-diphenyl-1,3,5-triazin-2-yl) phenyl)-5 H-benzofuro[3,2-c]carbazole, or oBFCzTrz, was discussed in Zhang, X. et al. High performance blue-emitting organic light- emitting diodes from thermally activated delayed fluorescence: a guest / host ratio study. J. Appl.Phys.124, 055501. https: / / doi.org / 10.1063 / 1.5041447 (2018). 2-[4-(Diphenylamino)phenyl]-10,10-dioxide-9 H- thioxanthen- 9- one, or TXO-TPA, was purchased from Luminescence Technologies Corporation. 2,7-bis(9,9-dimethylacridin-10(9 H)-yl)-9,9-dimethyl-9 H- thioxanthene 10,10-dioxide, or DMTDAc, was purchased and used as is from Luminescence Technologies Corporation.

[0074] Additional considerations for the materials chosen for this device include photostability and efficiency. Some of the emitters selected for this study have been used for high stability OLED architectures, such as TCZPBOX DMTDAc, TXO-TPA, and oBFCzTrz, have been demonstrated to have low aggregation as well, an approach that may result in highphotostability. This approach paves the way for higher device stability since the emitter dyes are operated in photoluminescence (PL), where the usual OLED degradation mechanisms of high-energy triplet interactions and carrier imbalance are not present. Other embodiments can utilize TADF emitters with larger FWHM, as most emitting materials have been developed for display applications requiring narrow spectra with low FWHM for color purity.

[0075] Fabrication

[0076] The device fabrication process began with creating the CAD file for the encapsulation that houses the light-conversion layer based on the dimensions of the beam spot size of the excitation LED. This process itself also allows the creation of built-in beam-steering and focusing structures, such as lenses. The design was printed in Clear v4 resin by FormLabs, using a FormLabs Form 2 SLA system. With this method, up to 60 samples were fabricated per batch.

[0077] Resin formation comprised blending the Clear v4 resin from FormLabs with the TADF compounds in powder form blended by magnetic stirring bar after sublimation and purification. A magnetic steering plate was used for 12–16 h depending on the material until the resin looked homogenous. All samples were stirred in amber vials to prevent photoinitiated cross-linking. This resin was chosen because it was readily available, relatively inexpensive, and compatible with high-throughput, high yield scalable additive manufacturing. After resin was filled into the encapsulation, the encapsulation was cured under 405 nm LED irradiance for 75 min at a temperature of 60 °C using a FormLabs Form Cure station.

[0078] Each resin sample was characterized by utilizing a 415 nm peak wavelength LED, for photoexcitation which was also used as the excitation source for the final WLED. The spectrum was then collected utilizing an OceanOptics USB2000 spectrometer. For each lab bench prototype device consisting of a VLED and encapsulated TADF light conversion layer was controlled by Keithley 2400. VLED model A007-UV410-48 was used, though in principle, other VLEDs with emission peak wavelength near 415 nm suitable for high power applications can be used.

[0079] Samples e-3, e-34, e-89, and e-100 were irradiated with an estimated 30.3 mW, 30.3 mW, 30.3 mW, and 57.8 mW respectively for spectrum characterization, corresponding to operating currents of 1 to 2 mA.

[0080] Data processing

[0081] Data set of over 1500 WLED SPD data was downloaded as provided by measurements.

[0082] WOLED SPD data was collected by measuring OLEDWorks OLED panels, measured in-house using OceanOptics USB2000 and powered by the OLEDWorks SDK which includes current driver and power supply.

[0083] Seoul Semiconductor Sunlike WLED data was digitized from datasheet using Origin 2020, datasheet available online at http: / / www.seoulsemicon.com / en / product / spec / _91_SunLike_92_%20SAWS0661A / 37files / 1469 / 37.html.

[0084] Hybrid rare earth free WLED comprised two organic emitters in PMMA matrix, data was digitized using Origin 2020 from plots in Menéndez-Velázquez, A., Morales, D. & García- Delgado, A. B. Sunlike white light-emitting diodes based on rare-earth-free luminescent materials. Materials. 15, 1680 (2022). All datasets were equalized by scaling such that luminous power was 250 photopic lux.

[0085] It is to be understood that the embodiments and claims disclosed herein are not limited in their application to the details of construction and arrangement of the components set forth in the description and illustrated in the drawings. Rather, the description and the drawings provide examples of the embodiments envisioned. The embodiments and claims disclosed herein are further capable of other embodiments and of being practiced and carried out in various ways. Also, it is to be understood that the phraseology and terminology employed herein are for the purposes of description and should not be regarded as limiting the claims.

[0086] Accordingly, those skilled in the art will appreciate that the conception upon which the application and claims are based may be readily utilized as a basis for the design of other structures, methods, and systems for carrying out the several purposes of the embodiments and claims presented in this application. It is important, therefore, that the claims be regarded as including such equivalent constructions.

[0087] Furthermore, the purpose of the foregoing Abstract is to enable the United States Patent and Trademark Office and the public generally, and especially including the practitioners in the art who are not familiar with patent and legal terms or phraseology, to determine quickly from a cursory inspection the nature and essence of the technical disclosure of the application. The Abstract is neither intended to define the claims of the application, nor is it intended to be limiting to the scope of the claims in any way.

Claims

CLAIMS What is claimed is:

1. A spectrally tunable light source, comprising:a plurality of light converters, each light converter comprising a thermal activated delay fluorescence (TADF) material and a light source configured to direct light on the TADF material, wherein the TADF material is configured to emit light having a predetermined range of wavelengths in response to light from the light source; and a controller configured to control the light source of each of the plurality of light converters to alter a light output of the plurality of light converters.

2. The spectrally tunable light source of claim 1, wherein the plurality of light converterscomprise a first light converter configured to emit light having a first predetermined range of wavelengths and a second light converter configured to emit light having a second predetermined range of wavelengths.

3. The spectrally tunable light source of claim 2, wherein the first light convertercomprises a first TADF material, and wherein the second light converter comprises a second TADF material.

4. The spectrally tunable light source of claim 1, wherein the light source of each of theplurality of light converters comprises a light emitting diode.

5. The spectrally tunable light source of claim 4, wherein the light emitting diode isconfigured to emit light having a wavelength of 380 nm to 750 nm.

6. The spectrally tunable light source of claim 1, wherein the controller is configured tocontrol the light source of each of the plurality of light converters to alter a wavelength of light output of the plurality of light converters.

7. The spectrally tunable light source of claim 1, wherein the controller is configured tocontrol the light source of each of the plurality of light converters to alter an intensity of light output by the plurality of light converters.

8. The spectrally tunable light source of claim 1, wherein the controller is configured tocontrol whether each light source of the plurality of light converters is on or off.

9. The spectrally tunable light source of claim 1, wherein the controller is configured tocontrol an intensity of light emitted by each light source of the plurality of light converters.

10. The spectrally tunable light source of claim 1, wherein a first portion of the plurality oflight converters are configured to emit light having a first range of wavelengths and a secondportion of the plurality of light channels are configured to emit light having a second range of wavelengths.

11. A spectrally tunable light source, comprising:a first light converter, comprising: a first emitter comprising a first TADF material; and a first light source configured to illuminate the first emitter, wherein the first emitter is configured to emit light having a first range of wavelengths in response to illumination by the first light source; a second light converter, comprising: a second emitter comprising a second TADF material; and a second light source configured to illuminate the second emitter, wherein the second emitter is configured to emit light having a second range of wavelengths in response to illumination by the second light source; and a controller configured to control an output of the first and second light sources to alter a light output by the spectrally tunable light source.

12. The spectrally tunable light source of claim 11, further comprising:a third light converter, comprising: a third emitter comprising the first TADF material; and a third light source configured to illuminate the third emitter, wherein the third emitter is configured to emit light having the first range of wavelengths in response to illumination by the third light source; a fourth light converter, comprising: a fourth emitter comprising the second TADF material; and a fourth light source configured to illuminate the fourth emitter, wherein the fourth emitter is configured to emit light having the second range of wavelengths in response to illumination by the fourth light source, wherein the controller is further configured to control an output of the third and fourth light sources to alter a light output by the spectrally tunable light source.

13. The spectrally tunable light source of claim 11, wherein the first and second lightsources each comprise a light emitting diode.

14. The spectrally tunable light source of claim 13, wherein the light emitting diodes areconfigured to emit light having a wavelength of 380 nm to 750 nm.

15. The spectrally tunable light source of claim 11, wherein the controller is configured tocontrol the first and second light sources to alter a wavelength of the light output by the spectrally tunable light source.

16. The spectrally tunable light source of claim 11, wherein the controller is configured tocontrol the first and second light sources to alter an intensity of the light output by the spectrally tunable light source.

17. The spectrally tunable light source of claim 11, wherein the controller is configured tocontrol whether the first and second light sources are on or off.

18. The spectrally tunable light source of claim 11, wherein the controller is configured tocontrol an intensity of light emitted by each of the first and second light sources.

19. A method of emitting light, comprising:providing a plurality of light converters, each light converter comprising a thermal activated delay fluorescence (TADF) material and a light source configured to direct light on the TADF material, wherein the TADF material is configured to emit light having a predetermined range of wavelengths in response to light from the light source; and controlling the light source of each of the plurality of light converters to alter a light output of the plurality of light converters20. The method of claim 19, wherein the plurality of light converters comprise a first lightconverter configured to emit light having a first predetermined range of wavelengths and a second light converter configured to emit light having a second predetermined range of wavelengths.

21. The method of claim 20, wherein the first light converter comprises a first TADFmaterial, and wherein the second light converter comprises a second TADF material.

22. The method of claim 19, wherein the light source of each of the plurality of lightconverters comprises a light emitting diode.

23. The method of claim 22, wherein the light emitting diode is configured to emit lighthaving a wavelength of 380 nm to 750 nm.

24. The method of claim 19, wherein controlling the light source of each of the plurality oflight converters alters a wavelength of light output by the plurality of light converters.

25. The method of claim 19, wherein controlling the light source of each of the plurality oflight converters comprises controlling whether each light source of the plurality of light converters is on or off.

26. The method of claim 19, wherein controlling the light source of each of the plurality oflight converters alters an intensity of light emitted by each light source of the plurality of light converters.

27. The method of claim 19, wherein a first portion of the plurality of light converters areconfigured to emit light having a first range of wavelengths and a second portion of the plurality of light converters are configured to emit light having a second range of wavelengths.

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