CaAlSiN3:Eu/glass composite film in reflective configuration: A thermally robust and efficient red-emitting color converter with high saturation threshold for high-power high color rendering laser lighting

To achieve high color rendering and proper color temperature, a red color converter is essential for phosphor-converted white lighting devices. CaAlSiN₃:Eu²⁺ (CASN) is a highly suitable red phosphor for white light-emitting diodes. However, it can be hardly used in high-power laser lighting due to poor thermal/chemical performance of the phosphor/silicone resin mixture. A series of all-inorganic CASN-based phosphors (e.g., composite ceramic and phosphor-in-glass) were developed to avoid the use of resin. However, new challenges emerged: none of them showed sufficient luminous efficacy (i.e., >50 lm/W) and adequate saturation-threshold (i.e., >30 W or 10 W/mm²). Here, we report a facile fabrication of CASN/glass composite films using a simple and efficient blade-coating method. Upon 450 nm excitation, the resultant composite film presents a high internal quantum efficiency of ~83%, comparable to that of pristine CASN powder (~90%). When irradiated with a blue laser, the composite film shows a record high luminous efficacy of 82 lm/W. Furthermore, its saturation threshold was investigated in high power and high power density mode, respectively. When measured in high power mode, it shows a high saturation threshold over 29.7 W (1.75 W/mm²), thus achieving a high luminous flux of 1576 lm; when measured in high power density mode, it shows a saturation threshold of ~10.2 W/mm² (1.13 W). With abovementioned excellent properties, the CASN/glass composite film has great potential for use in high-power and high color rendering laser lighting.     

Emitting area limitation via scattering control in phosphor film realizing high-luminance laser lighting

One major benefit of laser lighting is the possibility to achieve very high luminance. In phosphor-converted laser lighting systems, a blue (pump) laser can be focused into a very small spot. However, after excitation of the phosphor, the white-light-emitting area usually increases considerably, which reduces the luminance parameter substantially. Herein, we design and investigate a highly scattering YAG:Ce/glass composite film with a porous microstructure. Both the glass/phosphor interfaces and the introduced pores act as scattering centers, which can confine the emission area effectively. The relationship between the spot size and the microstructure (porosity, phosphor-particle size, thickness) is elucidated. Under excitation with blue laser, the composite film shows a uniform white-light emission with high luminous efficacy (230 lm/W) and high saturation threshold (> 40 W/mm²), thus achieving a high luminous exitance of ～1239 lm/mm². With above excellent properties, the designed composite films show great potential for use in high-luminance laser lighting.     

High CRI white light-emitting phosphor-in-glass film for laser lighting applications by adding cyan phosphor BaSi2O2N2:Eu2+

PiGF (Phosphor-in-glass film) with high color rendering was successfully prepared at a low sintering temperature. The influence of sintering temperature, the mass ratio of glass and phosphor, and different fluorescent layers on the luminescence properties of PiGF was systematically studied. It is of note that the “cyan cavity” is significantly reduced due to the addition of “cyan phosphor” (BaSi₂O₂N₂:Eu²⁺). Under 455 nm blue light laser excitation, PiGF has the highest luminous efficiency of 94.55 lm/W and a white light composite PiGF with a correlated color temperature of 5500 K and a color rendering index of 95 can be obtained. In short, this work shows that the PiGF has great potential application in white light laser lighting.     

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.     

Highly reflective interface design for phosphor-in-glass converter enabling ultrahigh efficiency laser-driven white lighting

To address the problems of low luminous efficacy and poor thermal stability of reflective phosphor-in-glass (PiG) converter, a thermally robust and highly reflective PiG-boron nitride (BN)-aluminum nitride (AlN) converter was designed for enabling ultrahigh efficiency laser-driven white lighting. Benefiting from the ingenious sandwich design with the thermally conductive AlN substrate and highly reflective BN-glass interface, a La₃Si₆N₁₁:Ce³⁺ (LSN) PiG-BN-AlN converter achieves white light emission with a high luminous efficacy of 214.2 lm/W under the 3.15 W blue laser excitation, which is the best recorded value for the reflective PiG-based converters thus far, and the surface temperature of LSN PiG is low to 126 °C. Furthermore, the LSN PiG-BN-AlN converter incorporates CaAlSiN3:Eu²⁺ (CASN) red phosphor to enable high-quality white light emission with high luminous flux and good color quality. The results reveal that the designed PiG-BN-AlN converter provides a promising strategy for achieving ultrahigh efficiency laser-driven white lighting.     

Tunable chromaticity and enhanced luminous efficacy of white LEDs with phosphor-in-glass coating via multilayer screen-printing

The phosphor-in-glass (PiG) coating was fabricated via multilayer screen-printing and low-temperature sintering. The PiG coating consisted of Eu₂O₃-doped P₂O₅-ZnO-B₂O₃ (PZB) glass, Y₃Al₅O₁₂:Ce³⁺ (YAG:Ce) yellow phosphor, and CaAlSiN₃:Eu²⁺ (CASN:Eu) red phosphor. Eu₂O₃ and CASN:Eu were used to provide red emission for tunable chromaticity of white light-emitting diodes (LEDs), and surprisingly, the luminous efficacy was also enhanced. The impact of the variation in the B₂O₃ content on the PZB glass and the effect of Eu₂O₃, YAG: Ce, and CASN:Eu on the luminescent properties of the PiG coating were investigated. The glass matrix with 8 mol% B₂O₃ showed the lowest transition temperature and a suitable coefficient of thermal expansion. The spectra showed that the coating can be excited by blue light and produce yellow light and red light. The spatial distribution of the PiG coating was inspected by scanning electron microscopy, and it was observed that only a low erosion of phosphor by the glass matrix occurred. Furthermore, the white LEDs devices were constructed with the PiG coating on the blue LED chips. This method showed a decreased correlated colour temperature of 5137, a increased colour rendering index of 82.8 and an improvement in the luminous efficacy. The PiG coating for tunable chromaticity and enhanced luminous efficacy of white LEDs shows potential for application.     

On the luminance saturation of phosphor-in-glass (PiG) films for blue-laser-driven white lighting: Effects of the phosphor content and the film thickness

To investigate the luminance saturation in high-power blue-laser-driven solid state lighting, the Y₃Al₅O₁₂: Ce (YAG)-based PiG films was co-fired with a high thermally conductive sapphire substrate. When the PtG ratio or the thickness of the PiG film increases, the luminance saturation becomes worse and both of the luminous flux and luminous efficacy decrease. With an additional sapphire substrate coated with an anti-reflection layer on one side and a blue-pass filter on another side attached to the PiG film, the film shows an improvement in luminous flux and efficacy, and produces the white light with a luminous flux of 1709 lm, a luminous efficacy of 211 lm W^?1 and a correlated color temperature of 6602 K under the maximum (10.3 W mm^?2) blue laser light excitation. It indicates that the PiG film could be applied in high power laser-driven solid state lighting when its microstructure is carefully tailored.     

Tunable chromaticity and high color rendering index of WLEDs with CaAlSiN3:Eu2+ and YAG:Ce3+ dual phosphor-in-silica-glass

Phosphors-in-glass (PiG), which serves as a potential bi-replacement of both phosphors and organic encapsulants in high-power white light-emitting diodes (WLEDs), has captured much attention due to its high thermal stability and excellent luminescent properties. However, due to the high-temperature sensitivity and the chemical reactions between phosphors with glass matrix, a variety of phosphors, especially red phosphors could be hardly dispersed into the glass without thermal quenching and decomposition, which greatly limits the improvement of color rendering index and chromaticity tunability of the WLEDs. In this study, adopting the mesoporous silica (FDU-12) and commercial phosphors as raw materials, the phosphors-in-silica-glasses (PiSGs) embedded with red phosphor CaAlSiN₃:Eu²⁺ and yellow phosphor YAG:Ce³⁺ have been successfully prepared at low sintering temperature (950°C) and short preparation time (10 minutes) using spark plasma sintering. Owing to the well preservation of the originally emissive properties of the embedded phosphors, the warm WLEDs with tunable chromaticity and exhibited a superior performance with LE of 133 lm/W, CCT of 3970 K and CRI of 81 were fabricated by encapsulating the as-prepared PiSGs on the blue chips. Moreover, the PiSG composite exhibits a high thermal conductivity up to 1.6 W/m·K.     

Highly thermal conductive red-emitting AlN-CaAlSiN3:Eu2+ composite phosphor ceramics for high-power laser-driven lighting

Thermally robust red-emitting phosphor ceramics are urgently required for laser lighting and displays with high luminance and better color saturation. The most promising CaAlSiN₃:Eu ceramics have a low thermal conductivity of 4.2 W m^?1 K^?1 and a small luminance saturation of 0.5 W, making it hard to be used under high power laser irradiation. In this work, we incorporated AlN into the CaAlSiN₃:Eu ceramic to produce red-emitting AlN-CaAlSiN₃:Eu composite phosphor ceramics by spark plasma sintering. The fully densified phosphor ceramics have the highest thermal conductivity reported so far (53.5 W m^?1 K^?1), which is about 13 times higher than the reported one. The luminance saturation of the composite ceramics occurs at a high threshold of 4.2 W under blue laser excitation, enabling them to be used for high power laser lighting. This work provides an idea of tackling the microstructure of nitride phosphor ceramics and of preparing thermally robust red-emitting color converters.     

Highly thermal stable and color tunable composite fluorescent ceramics for high-power white LEDs

All-inorganic fluorescent materials with high luminescence efficiency, high thermal stability and adjustable spectrum are urgently needed, especially for high-power white LEDs. In this work, Y_2.84Lu_0.1Al₅O₁₂: 0.06Ce³⁺ fluorescent ceramics were prepared firstly by vacuum sintering technology, and then Y_2.84Lu_0.1Al₅O₁₂: 0.06Ce³⁺/SrAlSiN₃: Eu²⁺ composite fluorescent ceramics were synthesized by technology screen-printing and laser ablation. Under 460 nm excitation, the composite fluorescent ceramic exhibits a broad emission band from 500 nm to 675 nm, which is attributed to the 5d → 4f transitions of Ce³⁺ and Eu²⁺ ions, respectively. By controlling the screen-printed times, the color coordinates of the composite fluorescent ceramics could be tuned from (0.3125, 0.2437) to (0.4106, 0.3824), and the correlated color temperature can vary from 3296 to 9689 K. In particular, the thermal stability of composite fluorescent ceramics is improved obviously after laser ablation. At 423 K, the luminescence intensity at 535 nm and 620 remains 91% and 94% of that at room temperature, respectively. Combining a 460 nm blue chip and the composite fluorescent ceramic, a white LED with CRI = 90, and the maximum luminous efficiency can be up to 148 lm/W. Our results indicate that Y_2.84Lu_0.1Al₅O₁₂: 0.06Ce³⁺/SrAlSiN₃: Eu²⁺ composite fluorescent ceramics could be used in high-power white LEDs.     

Investigation of an LuAG:Ce translucent ceramic synthesized via spark plasma sintering: Towards a facile synthetic route,robust thermal performance,and high-power solid state laser lighting

The aim of this study is to investigate a thermally robust green-yellow color converter for high-power solid state laser lighting applications. LuAG:Ce translucent ceramics (TCs) were synthesized via the spark plasma sintering (SPS) technique and LiF was used as additive. The as-prepared ceramics show remarkably superior thermal and luminescent properties: a high external quantum efficiency (77%), a low thermal quenching (4.1% drop at 200 °C), a good thermal conductivity (6.3 W m^?1K^?1), and a high reliability (only a 1.9% drop after 1000 h, at 85 °C and 85% humidity). A prototype lamp using the TC (and a 450 nm laser diode), with the increasing driving power (up to 8.7 W), shows increasing luminous flux (238–472 lm) with stable luminous efficiency (54.3-56.6 lm/W). This indicates that the translucent ceramic can be used for high-power laser-lighting.     

Ce:YScAG phosphor-converted transparent ceramics with high thermal saturation and weak concentration quenching for LED and LD white lighting

In the high-power white light LEDs/LDs area, obtaining phosphor-converted materials with high thermal stability and high luminous emittance with proper blue/yellow light ratio has been the main challenge in recent years. In this study, a group of (Ce_xY_1-x)₃(Sc_yAl_1-y)₅O₁₂ transparent ceramics with high optical quality were proposed to rise to that challenge. Their spectra were regulated by incorporating Sc³⁺, showing blue shifted emission bands (peak position from 554 nm–538 nm), blue shifted excitation bands (462–445 nm) and narrowed full width at half maxima (120–112 nm). Significantly, the prepared Ce:YScAG transparent ceramics (TC) exhibited decent thermal quenching performance with the photoluminescence intensity at 150 °C maintaining 88.7% of its original value at room temperature. The Sc incorporation impacted the atoms’ occupation and distance, crystal field splitting and energy band structure. Under remote LD excitation mode, the luminous efficiency of the prepared Ce:YScAG TC can achieve 164.8 lm/W. And even if the Ce³⁺ doping reaches 2.0 at%, the LE can still maintain 117.8 lm/W, exhibiting decent concentration quenching characteristic. Consequently, Ce:YScAG TCs have great potential as promising phosphor-converted materials in future high-power LED and LD white lighting.     

Phosphor-SiO2 composite films suitable for white laser lighting with excellent color rendering

Currently, phosphor composite films draw much attention in white laser lighting. In this work, we developed a novel phosphor-SiO₂ film via a mild method, which avoiding the phosphor degradation. Commercial colloidal silica was elected as the source of SiO₂ and acted as an inorganic binder, gap filler and a protective coating layer. Composite films comprised of mixed Lu₃Al₅O₁₂:Ce³⁺ and CaAlSiN₃:Eu²⁺ phosphors exhibit a uniform dense strucure and strong adhesion to the substrate. When excited by blue diodes laser, the optimal film exhibits excellent thermal stability (it maintains 89.1 % of the room-temperature intensity at 200 °C), super resistance against laser irradiation (12.9 W/mm²), a broad emission spectra with a full width at half maximum of 180 nm and a high luminous efficiency (183 lm/W). The color rendering index of the film was improved to 85. These outstanding properties indicate that the derived films are a promising candidate for white laser lighting.     

High lumen density of Al2O3-LuAG: Ce composite ceramic for high-brightness display

Thermally robust and highly efficient green-emitting luminescent ceramics are gradually attracting great attention as promising phosphors using in high-brightness laser phosphor display to reduce serious speckle noise as well as high cost. However, lumen density is still seriously restricting their potential applications especially under high-power density laser due to insufficient absorption of blue laser and significant thermal quenching. Here, we report an Al₂O₃-LuAG: Ce composite ceramic phosphor (CCP) for high-brightness laser phosphor display. Owing to good optical properties and high thermal conductivity of Al₂O₃, the Al₂O₃-LuAG: Ce CCP shows high photoluminescence quantum yield (79.6%), low thermal quenching (only 3.2% loss in luminescence at 200°C), and high thermal conductivity (18.9 W·m⁻¹·K⁻¹). Moreover, the Al₂O₃, as scattering centers, enhances the Rayleigh–Mie scattering of the blue laser, and hence the absorption of the Al₂O₃-LuAG: Ce CCP exhibits a remarkable improvement (~2.3 times) at 450 nm. Finally, with optimized thickness (0.3 mm) of Al₂O₃-LuAG: Ce CCP, an excellent luminous efficiency (216 lm·W⁻¹) and outstanding lumen density (6129 lm·mm⁻²) of the green-emitting light source was obtained by driving under a high-power density (28.33 W·mm⁻²) blue laser. All of those validate the suitability of the Al₂O₃-LuAG: Ce CCP for high-brightness display.     

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.     

Porous Ce:YAG ceramics with controllable microstructure for high-brightness laser lighting

In order to meet the increasing demand for high-power laser diode lighting and displays, phosphor converters with high-brightness and high-directionality ought to be constructed to enhance the luminance and luminous efficacy. However, the pores formed during the sintering of phosphor ceramics affect the scattering effect and directionality of light. Therefore, porosity optimization and pore size regulation need to be explored. In this work, a series of Ce:YAG ceramics with various porosities and pore sizes were prepared. The influences of porosity and pore size on the microstructure, light confinement ability, and optical properties of Ce:YAG ceramics were studied. The ceramic phosphor with a porosity of 10 vol.% and a pore size of 3 μm exhibits a good spot confinement ability and shows a high luminous flux value of 3430 lm and a central luminance (1669 592 cd/m²) under blue laser excitation. The 10 vol.% Ce:YAG ceramic phosphor with a pore size of 5 μm has the highest emission intensity and gives a maximum luminous efficacy of 268 lm/W and a luminous flux of 4020 lm under 30 W/mm² blue laser excitation. Thus, the porous Ce:YAG ceramics are expected to be a promising candidate for high-brightness laser lighting and projection applications.     

Carbon-free synthesis and luminescence saturation in a thick YAG:Ce film for laser-driven white lighting

Good thermal dispersion is essential for phosphors used in laser-lighting applications. Luminescent films naturally show better thermal dispersion than bulk phosphor because the distance to the supporting substrate is shorter, which facilitates heat dissipation. However, the underlying mechanism for luminescence saturation in films is still unclear. In addition, the synthesis of luminescent films always involves the use of carbon-rich organic materials, which can introduce both pores and carbon residues. Here, we present a facile sol–gel route to synthesize YAG:Ce thick films suitable for laser lighting applications. Inorganic aluminum hydroxides are used as gelling agent, which solves the carbon residue problem. A series of YAG:Ce films of different thicknesses was produced at relatively low temperature (975 °C). The YAG:Ce film shows no luminescence saturation under 4.1 W blue laser excitation. This means this approach represents a strong potential candidate for applications like automotive headlamps and many other devices.     

Phosphor‐in‐glass thick film formation with low sintering temperature phosphosilicate glass for robust white LED

Phosphor‐in‐glass (PiG) thick film was fabricated on a borosilicate glass substrate using a conventional screen printing method and employing phosphosilicate glass to allow low‐temperature sintering. The vehicle content and sintering temperature were optimized to form a thick film with a thickness of ~50 μm. Commercial yellow (Y₃Al₅O₁₂:Ce³⁺) and red (CaAlSiN₃:Eu²⁺) phosphors were successfully incorporated within the glass matrix and then sintered at 550°C. Color‐tunable white LEDs were achieved using the PiG thick films as a color converter by varying the glass to phosphor (GtP) ratio. The high luminous efficacy of up to ~120 lm/W and high color rendering index of up to 89 in combination with the thermal quenching property prove the practical feasibility of the PiG thick films for high‐power/high‐brightness LED applications.     

High-efficiency phosphor-in-glass with ultra-high color rendering indexing for white laser diode lighting

Stable color converters exhibiting high color rendering index have drawn researchers’ attention for their applications in high-quality white laser lighting. In this study, we develop the multi-color phosphor-in-glass (PIG) with the weight ratio of green-emitting (Y₃Al_3.08Ga_1.92O₁₂:Ce³⁺) to red-emitting (CaAlSiN₃:Eu²⁺) phosphor powders (10/1–18/1) by low temperature co-sintering method. The obtained composite material displays an outstanding optical and thermal performance, including a high internal quantum efficiency of 84.2%, a high transparency of 45% in the visible region and a low thermal quenching (it remains 86% at 448 K). By integrating 450 nm blue laser diodes with optimized multi-color PIG, the white light with a maximum luminous flux of 258 lm and a luminous efficiency of 137 lm/W is achieved for the first time. Additionally, considering the white balance, by tailoring the weight ratio of green-emitting to red-emitting phosphor and the thickness of PIG, the 14/1 PIG at fixed thickness of 0.75 mm produces pure white light with ultra-high color rendering index of 95.2 and a high luminous efficiency of 120.9 lm/W under power density of 2.39 W/mm² irradiation. The above superior characteristics imply that the multi-color PIG is an ideal candidate for high-quality white laser lighting applications.     

Nanostructured NdF3 glass ceramic: An efficient bandpass color filter for wide-color-gamut white LED

Up-to-date LED-lit LCD technology pursues a wide color gamut to ensure reproduction of all natural colors. Herein, a novel NdF₃ glass ceramic was developed as bandpass color filter for pc-wLEDs. In-depth microstructural and optical analyses reveal the alteration of local environment of Nd³⁺ from the oxide-amorphous matrix to the fluoride-crystalline phase after crystallization. A prototype pc-wLED is constructed by coupling all-inorganic “YAGG:Ce³⁺+CASN:Eu²⁺” phosphor-in-glass plate and NdF₃ glass ceramic plate with blue-emitting chip in a stacked configuration. Thanking to the efficient absorption from hypersensitive Nd³⁺: ⁴I_9/2 → ⁴G_5/2, ²G_7/2 transition, the electroluminescent spectral profile of phosphors can be well separated into two narrowed bands in the green and red regions, and so an improved color gamut of 78.8% is achieved. The present work demonstrates an efficient route for wide-color-gamut white LED in a facile and cost-effective way.