High Brightness White Light Research Articles

Unique sandwich and microstructure design of phosphor-in-glass film for high brightness laser-driven white lighting

All-inorganic phosphor-in-glass (PiG) converter withstanding high power laser excitation has garnered attention for laser-driven white lighting, while its poor heat dissipation and low fluorescence conversion efficiency has been serious challenges in high-brightness white lighting. Herein, a thermally robust PiG film converter with a sandwich phosphor structure and microstructure interface was designed for ultrahigh-brightness laser-driven white lighting. The yellow-emitting YAG PiG film was thermocompression bonded to microstructure sapphire (MS) and planar alumina (PA) to construct the MS-PiG-PA converter. The YAG PiG film possess higher luminescence intensity than YAG phosphor and was tightly attached to sapphire and alumina without microcracks. Benefiting from the double-sided heat dissipation design and microstructure interface light field strengthening effect, the MS-PiG-PA converter emits ultrahigh luminous flux white light (5197 lm) at power density of 30 W/mm2 and displays excellent CRI and CCT stability. The MS-PiG-PA converter has a lower working temperature, higher saturation threshold and luminous efficacy.

White electroluminescence of diamond/boron/diamond/SrTiO3 composite film

Diamond/boron/diamond/SrTiO3 composite film (BDDSCF) electroluminescent (EL) devices were deposited by microwave plasma chemical vapor deposition (MPCVD) technology and vacuum electron beam vapor deposition (EBVD) technology. The samples were characterized by field emission scanning electron microscopy (FE-SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and energy dispersive spectroscopy (EDXS). The current-voltage (I–V) characteristic of the sample was measured by an adjustable direct current power supply. The EL spectra of the samples obviously exhibit three emission peaks, which are centered at 440 nm (blue area), 592 nm (yellow area) and 736 nm (red area). In the indoor environment, it can be observed by the naked eye that the surface of the sample will emit uniform and high brightness white light. The blue peak is from the recombination of the conduction band electron in SrTiO3 film and the quasi-acceptor (trapped hole) associated with oxygen vacancy, the yellow peak is caused by the self-trapping exciton (STE) recombination caused by oxygen vacancies in SrTiO3, and the red peak is attributed to the silicon impurity centers or carbon neutral vacancy in diamond films.

Nitride phosphor-in-glass films enabling high-performance white light in transmissive and reflective laser lighting

Phosphor-converted laser lighting has become a credible candidate in next-generation high-brightness white lighting, and the configuration types of phosphor converters have a great influence on the opto-thermal performances of laser lighting. In this work, we proposed nitride phosphor-in-glass films (PIGFs) for high-brightness laser lighting and investigated the opto-thermal performances of PIGFs in transmissive (T) and reflective (R) modes. The Y-PIGFs were prepared by low-temperature sintering a mixture of yellow-emitting La3Si6N11:Ce3+ (LSN) phosphor and borosilicate glass, and the Y/R-PIGFs were achieved by incorporating red-emitting CaAlSiN3:Eu2+ (CASN) phosphor into the Y-PIGFs. The PIGFs display higher thermal stability and luminescence intensity than the raw phosphors. By tailoring the thickness of Y-PIGFs, the Y-PIGF with a film thickness of 75 μm achieves the luminous efficacy of 199.4 lm/W and 91.5 lm/W in the T mode and R mode, respectively, and the PIGF realizes the highest luminous efficacy of 207.8 lm/W by collecting backward light in the T mode. At the CASN/LSN ratio of 0.20, the Y/R-PIGF enables high-quality white light with a color rendering index (CRI) higher than 89. Furthermore, under 4.82 W laser excitation, the central temperatures of Y-PIGF in the T-mode and R-mode are only 98 °C and 67.4 °C, respectively. The results indicate that the PIGFs enable high-performance white laser lighting with distinct opto-thermal properties by adjusting configuration types.

Enhancing opto-thermal performances of white laser lighting by high reflective phosphor converter

Phosphor-converted white laser lighting has been considered as a promising candidate in next-generation high-brightness lighting. However, the color converter confronts the inevitable roadblock of low light extraction efficiency and poor thermal stability in reflective white laser diodes (LDs). Herein, a high reflective converter of phosphor-in-glass film-BN layer-Al substrate (PiG-BN-Al) was prepared for high-brightness white laser lighting. The effects of laser power and excitation time on opto-thermal performances of PiG-BN-Al-based converter were investigated and compared with the traditional PiG-Al-based converter. Attributing to the high reflectivity of BN glass composite and the high thermal conductivity of Al substrate, the PiG-BN-Al-based converter achieves a luminous flux of 458.6 lm at a laser power of 3.15 W, which is about 70 % higher than the PiG-Al-based converter. Furthermore, the PiG-BN-Al-based converter still remains low surface temperature of 46.4 °C under the continuous laser excitation. The PiG-BN-Al-based converter provides an effective strategy to enhance the opto-thermal performances of white laser lighting. • A high reflective PiG-BN-Al-based converter was prepared for white laser lighting. • The PiG-BN-Al-based converter presents high luminous flux of 458.6 lm. • The PiG-BN-Al-based converter shows thermal stability and low surface temperature. • The converter enhances the opto-thermal performances of white laser lighting.

Heat-conducting LSN:Ce-in-glass film on AlN substrate for high-brightness laser-driven white lighting

Laser diodes (LDs) combined with color converters have been considered as new-generation high-brightness white light source. Whereas, the luminescence of phosphor materials is easily influenced by accumulated heat originating from laser-driven conversion. In order to alleviate the thermal effect under focused laser of high-power, we proposed a high-luminescence laser-driven color converter of heat-conducting La3Si6N11:Ce3+ (LSN:Ce) phosphor-in-glass (PiG). The LSN:Ce nitride phosphor exhibits excellent opto-thermal property. The LSN:Ce-PiG-AlN converter was fabricated by sintering the LSN:Ce-PiG layer (∼50 μm) upon a AlN ceramic substrate. Due to excellent luminescence of LSN:Ce and high thermal conductivity of AlN, the LSN:Ce-PiG-AlN converter achieves a luminous flux (LF) of 376.1 lm, a luminous efficiency (LE) of 158 lm/W, and a correlated color temperature (CCT) of 4462 K under 2.39 W laser excitation. In addition, the temperature of PiG film surface still stays low level (<150 °C) when driven by 4.82 W laser irradiation. The proposed LSN:Ce-PiG-AlN converter is a high-performance and promising phosphor converter for high-luminescence white laser lighting.

Enhancing Thermal Stability of Laser-Driven Phosphor Converter by Utilizing Copper Powder Sintering Framework/Paraffin

Laser-driven white light illumination is considered as the next generation of high brightness white light source. The most common way to achieve laser-based white light is using a blue laser to excite phosphor/ silicone converter (reference converter). However, the relatively low thermal conductivity of phosphor limits most of the heat to its surface and cannot be dissipated effectively. In this work, a converter with copper sintering powder framework/paraffin (CPSF/P) embedded into the phosphor/silicone is proposed. As an internal heat transfer channel, copper powder sintering framework (CPSF) transfers heat to paraffin coated in porous skeleton, and then paraffin absorbs the generated heat through solid–liquid phase transition, which effectively dissipates the heat concentrated on the phosphor surface and improves its thermal stability. Under high-power laser excitation of 7.74 W, the surface temperature of the reference converter is up to 660 °C, while the maximum temperature of the CPSF/P converter is only 139 °C, which is reduced by 521 °C (78.9%). The results show that the proposed CPSF/P converter can withstand higher excitation power and show better thermal stability than the reference converter, which is helpful to obtain higher color stability. This provides an efficient heat dissipation scheme for high-power laser-driven lighting.

Heat Dissipation Enhancement of Phosphor-Converted White Laser Diodes by Thermally Self-Managing Phosphor-in-Glass

Laser-driven white lighting has been considered as a next-generation high-brightness white lighting source. Thermally stable color converter is an essential down-conversion material for phosphor-converted white laser diodes (pc-wLDs), which inevitably endures high-density laser excitation and huge heat shock from conversion loss. In this work, we proposed a thermally self-managing phosphor-in-glass (PiG) converter to enhance the heat dissipation of reflective pc-wLDs. The PiG converter was prepared by printing and sintering a phosphor glass film on the cold side of thermoelectric cooler (TEC). By controlling the input current of TEC, the heat generated from phosphors under high-power laser excitation was effectively and initiatively dissipated into the ambient environment due to the Peltier effect of TE materials. As the laser power (LP) increases from 0.73 to 5.6 W, the working temperature of PiG film slowly increases from 2.3°C to 6.1°C. The maximum temperature of PiG film is reduced by 61.1 °(~91%) at the LP of 5.6 W. Furthermore, the PiG-TEC-based pc-wLD achieves a cool white light and stable light quality under various LPs. At the LP of 4.5 W, the correlated color temperature (CCT) of pc-wLD is 6449 K, and the chromaticity coordinate of pc-wLD is (0.3139, 0.3274). The results indicate that the proposed PiG-TEC converter enhances the thermal performance of high-brightness laser-driven white lighting.

Ternary solid solution phosphors Ca1-x-yLixAl1-x-ySi1+x+yN3-yOy:Ce3+ with enhanced thermal stability for high-power laser lighting

The discovery of thermally robust phosphors is essential to achieve efficient and stable luminescence in solid-state lighting devices, especial in high-power devices. Here, a novel ternary solid solution phosphor enabling to address this challenge is designed by introducing isostructural LiSi2N3 and Si2N2O into CaAlSiN3 lattice. The compound, Ca1-x-yLixAl1-x-ySi1+x+yN3-yOy:Ce3+ (CALSON:Ce), exhibits an excellent thermal stability with an integrated emission loss of only 9% at 200 °C, far smaller than that of the parent CaAlSiN3:Ce3+ (25%). The enhanced thermal stability is assigned to the broadened band gap (5.21 → 5.50 eV) upon the formation of solid solutions. Moreover, the new phosphor presents a broadband (full width at half maximum of 135 nm) yellow-orange emission peaking at 580 nm and shows a high external quantum efficiency of 41.5%. The excellent photoluminescence properties and thermal stability of CALSON:Ce thus enable it to be used under high-power laser excitation, and to produce high-brightness white light having a luminous flux of 392 lm (luminous emittance of 781 lm mm−2), a low correlated color temperature of 4349 K, and a high color rendering index of 70. This work suggests that creating multi-component solid solutions would be a general strategy for designing novel phosphors.

Ring Remote Phosphor Structure for Laser-Driven White Lighting

In this article, a ring remote phosphor (RRP) structure comprising an inverted-cone-lens encapsulant and a surrounding phosphor layer was developed and used for laser-driven white lighting. The inverted-cone-lens encapsulant in the structure redirects light from a blue laser diode (LD) to the surrounding phosphor layer, thus preventing intense light from hitting the phosphor layer on a small surface and, therefore, from considerably reducing luminous efficiency. The design of the inverted-cone-lens surface of the encapsulant was investigated, and 3-D ray-trace simulations were performed to confirm its light distributions. The RRP structure with an inverted-cone-lens encapsulant and a surrounding phosphor layer was fabricated to produce laser-driven white lighting, and the optical characteristics of the RRP structure with different phosphor concentrations were examined. The output luminous flux of the RRP samples increased with increased phosphor concentration, whereas the correlated color temperature (CCT) decreased with an increase in phosphor concentration. Therefore, the RRP structure can be used to generate efficiently high-brightness white light.

High luminous fluorescence generation using Ce:YAG transparent ceramic excited by blue laser diode

Solid-state laser lighting is an emerging technology, whereby high-brightness white light can be generated using blue laser diodes combined with a yellow-emitting phosphor. In this study, Ce:YAG transparent ceramic wafers with different cerium concentrations and thicknesses are prepared and their optical characteristics are measured. A transmission mode is used, wherein the phosphor ceramic is fixed onto an oxygen-free copper sink, whose temperature is accurately controlled, and excited using the blue laser diode. The recorded spectrum shows that blue laser light is completely converted to yellow light with a wavelength of 565 nm and width of 200 nm. Moreover, with varied temperatures of 10–80 °C, the luminous flux, spectrum, and color coordinates exhibit relatively stable. More importantly, the luminous flux is highest (2690 lm) when irradiated by a 19.5-W blue laser (with a center wavelength of 454 nm) for a Ce3+ dopant concentration of 0.5 mol% and a Ce:YAG thickness of 1.6 mm. Based on these results, the Ce:YAG transparent ceramic can be used as a potential phosphor material in applications of high-power solid-state laser lighting and laser display.

Polarisation fields in III-nitrides: effects and control

III-Nitrides are materials that have revolutionised the lighting industry allowing for the development of high brightness and efficiency white light emitting diodes (LEDs), enabling cost and energy savings at an unprecedented scale. However, there remain several obstacles to the further enhancement of the efficiency of LEDs, particularly for emission at longer wavelengths. The existence of polarisation fields as an inherent property of wurtzite III-nitride materials severely hampers LED performance. The origin of these fields due to the deviation from an ideal tetrahedral bonding structure and their relation to strain has been addressed in this review. The effect of the polarisation fields on the band structure of heterostructure quantum wells, known as the quantum confined stark effect, and its implications for the efficiency and spectral stability of LEDs have also been reviewed. Finally, the effectiveness and viability of several proposed methods of mitigating the harmful effects of the polarisation fields, such as the growth of III-nitrides on alternative planes, doping, strain engineering and growth of cubic GaN, have been addressed.

Single-crystal phosphors for high-brightness white lighting

Single-crystal phosphors for high-brightness white lighting

Evaluation of Thermally Stable Phosphor Screens for Application in Laser Diode Excited High Brightness White Light Modules

A study on the preparation of thermally stable phosphor targets based on yttrium aluminum garnet doped with cerium (YAG:Ce) when excited by a high power laser diode is described. The luminous flux, chromaticity and radial spectral flux of the targets along with their thermal stability have been determined when exposed to laser powers of up to 5000 mW. This report presents successful high brightness light sources with adjustable emission properties achieved by utilizing thermally stable phosphor targets excited by high power laser diodes.

Nanopatterned yttrium aluminum garnet phosphor incorporated film for high-brightness GaN-based white light emitting diodes

In this study, we fabricated high-brightness white light emitting diodes (LEDs) by developing a nanopatterned yttrium aluminum garnet (YAG) phosphor-incorporated film. White light can be obtained by mixing blue light from a GaN-based LED and yellow light of the YAG phosphor-incorporated film. If white light sources can be fabricated by exciting proper yellow phosphor using blue light, then these sources can be used instead of the conventional fluorescent lamps with a UV source, for backlighting of displays. In this work, a moth-eye structure was formed on the YAG phosphor-incorporated film by direct spin-on glass (SOG) printing. The moth-eye structures have been investigated to improve light transmittance in various optoelectronic devices, including photovoltaic solar cells, light emitting diodes, and displays, because of their anti-reflection property. Direct SOG printing, which is a simple, easy, and relatively inexpensive process, can be used to fabricate nanoscale structures. After direct SOG printing, the moth-eye structure with a diameter of 220nm was formed uniformly on the YAG phosphor-incorporated film. As a result of moth-eye patterning on the YAG phosphor-incorporated film, the light output power of a white LED with a patterned YAG phosphor-incorporated film increased to up to 13% higher than that of a white LED with a non-patterned film.

Incoherentized High-brightness White Light Generated Using Blue Laser Diodes and Phosphors&amp;mdash;Effect of Multiple Scattering&amp;mdash;

Incoherentized High-brightness White Light Generated Using Blue Laser Diodes and Phosphors&amp;mdash;Effect of Multiple Scattering&amp;mdash;

Heat Dissipation Design of High Power LED Headlamp

High brightness white light emitting diodes(LEDs) are very promising in many new illumination applications. This paper is to investigate the cooling solutions of a LED heallamp. Air cooling with heat sink were proved to be unsuitable. A cooling method based on heat pipe is adopted which is proved to be effective. Simulations were performed with Flotherm software to investigate the thermal permance.A sample of LED headlamp is fabricated based on the structure of a certain sedan combined headlamp. The testing results are in accordance with the simulation results

Liquid cooling of bright LEDs for automotive applications

With the advances in the technology of materials based on GaN, high brightness white light emitting diodes (LEDs) have flourished over the past few years and have shown to be very promising in many new illumination applications such as outdoor illumination, task and decorative lighting as well as aircraft and automobile illuminations. The objective of this paper is to investigate an active liquid cooling solution of such LEDs in an automotive headlights application. The thermal design from device to board to system level has been carried out in this research. Air cooling and passive liquid cooling methods were investigated and excluded as unsuitable, and therefore an active liquid cooling solution was selected. Several configurations of the active liquid cooling system were studied and optimisation work was carried out to find an optimum thermal performance.

High Brightness White Organic Light Emitting Devices Employing Phosphorescent Iridium Complex as RGB Dopants

An efficient phosphorescent white organic light-emitting diode (WOLED) was realized by using a bright blue-emitting layer, iridium (III) bis [(4, 6-di-fluoropheny)-pyridinato-N, C2’] picolinate doped 4.4’-bis (9-carbazolyl)-2, 2’-dimethyl-biphenyl, together with tris (2- Phenylpyridine) iridium and bis (1-phenyl-isoquinoline) acetylacetonate iridium (III) were codoped into 4,4’-N,N’-dicarbazole-biphenyl layer to provide blue, green, and red emission for color mixing. The device emission color was controlled by varying dopant concentrations and the thickness of blue and green-red layers as well as tuning the thickness of exciton-blocking layer. The maximum luminance and power efficiency of the WOLED were 37100cd/m2 at 17 V and 7.37lm/W at 5V, respectively. The Commission Internationale de 1’Eclairage (CIE) chromaticity coordinate changes from (0.41, 0.42) to (0.37, 0.39) when the luminance rangeed from 1000cd/m2 to 30000cd/m2.

Fluorene trimers with various 9,9′-substituents: The synthesis, characteristics, condensed state structures, and electroluminescence properties

The four fluorene-based trimers with various aromatic and alkyl substituents (T1–T4) are synthesized and characterized. These oligomers show the similar electronic absorption and emission characteristics (e.g., absorption peak at 351nm, and highly efficient deep blue emission at 394nm in solution), indicating that the major electronic properties of the core chromophore are essentially independent of the substituents. However, the condensed state structures and thermal properties of four trimers are found to be different from each other, from crystalline (full alkyl (T1) or full aromatic (T2) substituted trimers) to amorphous (mixed aromatic and alkyl (T4) substituted trimers). The effect of different condensed state structures on electroluminescence device properties is presented: The blue light-emitting devices with accordant structure of ITO/PEDOT:PSS/TCTA (40nm)/trimers (40nm)/BCP (10nm)/Alq3 (20nm)/LiF/Al exhibit different EL efficiency (2.9% of T2, 1.8% of T3 and 2.7% of T4). Using amorphous T4, the white light-emitting device of ITO/TCTA (40nm)/rubrene (0.1nm)/T4 (8nm)/Alq3(52nm)/LiF/Al is fabricated with high efficiency (6.15cdA−1), high brightness (9500cdm−2) and good white light CIE coordinates (0.32, 0.37).

Medium pressure mercury discharge for use as an intense white light source

In this paper, we demonstrate the possibilities that exist in developing a high brightness white light source. The lamp employs mercury at a few Torr and is operated with short pulses of the order of 1 µs at a frequency of 10 kHz. The emission spectrum is atomic in nature and the white light is the outcome of a relative enhancement of the mercury yellow lines at 577 and 579 nm with respect to the rest of the visible lines, which shifts the colour coordinates of the source towards the black body locus of the chromaticity diagram. The pulse operation of a lamp containing mercury at a vapour pressure of 20 Torr offers a greater near-UV and visible output compared to a phosphor-uncoated, low-pressure pulsed compact mercury discharge.