Color conversion properties of various thick-film phosphor-in-glasses depending on structural design for white LEDs

Thick-film phosphor-in-glasses (PiGs) were fabricated via a screen-printing method with various phosphor layer structures, to compose a white light emitting diode (LED). Green (Lu₃Al₅O₁₂:Ce³⁺) and red (CaAlSiN₃:Eu²⁺) phosphors were mixed, layered, and patterned on a glass substrate. The chromaticity of each structured PiG was tuned to achieve a white LED by varying phosphor content and thickness. The emission spectra and the related various color conversion properties, including color coordinates, correlated color temperature (CCT), color rendering index (CRI), luminous efficacy (LE) and the color gamut of the mounted PiGs with different phosphor layer structures were examined and compared. Time-resolved photoluminescence (TRPL) measurements of the white LEDs with various phosphor layer structural designs were also obtained and compared. It was observed that spectral variation depended on the PiG layer structure. A proper PiG layer structural design was discussed for practical applications.     

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.     

Gradient refractive index structure of phosphor-in-glass coating for packaging of white LEDs

A gradient refractive index (GRIN) structure, with a gradual increase in the refractive index from the glass substrate, was successfully obtained by multilayer screen printing for white light-emitting diodes (w-LEDs) packaging. Each phosphor-in-glass (PiG) coating consisted of B₂O₃–SiO₂–ZnO glass matrix and yellow phosphor. The gradually increased refractive index (1.62, 1.72, and 1.82) of glass matrices were obtained from higher molecular weight of La₂O₃ and WO_3. After sintering at 600°C, no obvious interface was observed and the phosphor particles were mixed thoroughly in the glass matrix. When the phosphor content was 50 wt%, the white-light emission was obtained. Compared with those based on the nongradient and low-refractive PiG coating, the luminous efficacy of w-LEDs constructed by the PiG coating with GRIN was enhanced. It shows that the GRIN structure is beneficial to improve the luminous efficacy of w-LEDs.     

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.     

Facile synthesis of the desired red phosphor Li2Ca2Mg2Si2N6:Eu2+ for high CRI white LEDs and plant growth LED device

The red emission with suitable peak wavelength and narrow band is acutely required for high color rendering index (CRI) white LEDs without at the cost of the luminous efficacy. Herein, the Li₂Ca₂Mg₂Si₂N₆:Eu²⁺ red phosphor was prepared with facile solid-state method using Ca₃N₂, Mg₃N₂, Si₃N₄, Li₃N, and Eu₂O₃ as the safety raw materials under atmospheric pressure for the first time, which shows red emission peaking at 638 nm with full width at half maximum (FWHM) of 62 nm under blue light irradiation and becomes the desired red phosphor to realize the balance between luminous efficacy and high CRI in white LEDs. The morphology, structure, luminescence properties, thermal quenching behavior, and chromaticity stability of the Li₂Ca₂Mg₂Si₂N₆:Eu²⁺ phosphor are investigated in detail. Concentration quenching occurs when the Eu²⁺ content exceeds 1.0 mol%, whereas high-temperature photoluminescent measurements show a 32% drop from the room-temperature efficiency at 423 K. In view of the excellent luminescence performances of Li₂Ca₂Mg₂Si₂N₆:Eu²⁺ phosphor, a white LEDs with CRI of 91 as a proof-of-concept experiment was fabricated by coating the title phosphor with Y₃Al₅O₁₂:Ce³⁺ on a blue LED chip. In addition, the potential application of the title phosphor in plant growth LED device was also demonstrated. All the results indicate that Li₂Ca₂Mg₂Si₂N₆:Eu²⁺ is a promising red-emitting phosphor for blue LED-based high CRI white LEDs and plant growth lighting sources.     

Phosphor‐in‐fluorescent‐glasses for high color rendering white light emitting diodes

Fluorescent glass frits were prepared and used to synthesize phosphor‐in‐fluorescent glass composites (PiFGs) to realize stable white light emitting diodes with high color‐rendering properties. Commercial red, green, and blue phosphors were co‐sintered and red phosphors were partially replaced by Eu³⁺ in glass frits. Phosphor‐in‐glass composites were placed on UV‐light emitting diodes (UV‐LEDs) to generate white light. Pure white light with a luminous efficacy=58.4 lm/W, general color rendering index R_a=87 and special color rendering index for strong red R₉=73 was realized with glass frits containing 7 mol% Eu₂O₃ and RGB ratio of 35:20:15. Luminous efficacy, R_a and R₉ increased as red phosphors were replaced by red‐fluorescent glass frits.     

Design of a CaAlSiN3:Eu/glass composite film: Facile synthesis,high saturation-threshold and application in high-power laser lighting

Even though CaAlSiN₃:Eu²⁺ (CASN) is, in many regards, a highly suitable red phosphor that can be used in white light-emitting diodes, it can hardly be used in high-power laser-lighting because of its low saturation-threshold. By using CASN-based composite ceramics, it is possible to increase the threshold but new difficulties appear. These include complex and expensive synthesis, while the saturation-threshold still has room for improvement. In this study, we prepare a CASN/glass composite film, using an industry-friendly blade-coating method. The film has a high internal quantum efficiency of 79%, which suggests low conversion loss. Under 1.17 W blue laser excitation, a high luminous efficacy of 21.0 lm/W can be obtained. More importantly, the composite film shows a record-high saturation-threshold of more than 12.7 W (∼320 W/cm²) blue laser excitation. With these outstanding properties, CASN/glass composite films may open doors towards commercially viable red color converters for high-power laser-lighting applications.     

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.     

Enhanced red emission and improved thermal quenching of CaAlSiN3:Eu2+ phosphors via boron doping

The development of high-performance phosphors is required for phosphor-converted white light-emitting diodes. However, most approaches are unable to achieve optimum emission intensity and thermal quenching simultaneously. Here, a series of CaAlSiN₃:Eu²⁺ (CASN:Eu²⁺) red-emitting phosphors doped with B were synthesized using field-assisted sintering technology. Compared with CASN:Eu²⁺, the B-doped phosphor exhibited high external quantum efficiency (EQE) and good thermal quenching performance. With boron doping, the EQE of CaAlSiN₃:Eu²⁺ shows an obvious growth, increasing from 48.83% to 70.68%. Meanwhile, thermal quenching performance has also been greatly improved, which is strongly associated with the band structure of Eu²⁺ and the crystal structure of CASN. The location of B in the crystal lattice was studied and the mechanism of improving thermal quenching via B doping was discussed in detail. Finally, a white LED fabricated by the combination of a GaN blue chip (450 nm) with the as-synthesized red phosphors and Y₃(Al, Ga)₅O₁₂:Ce³⁺ green phosphors (531 nm), shows a high color rendering index (Ra =91.6). This study offers a novel method to improve luminescence properties of CASN:Eu²⁺ red-emitting phosphors, which may broaden their application in solid-state lighting devices.     

Eu‐, Tb‐, and Dy‐Doped Oxyfluoride Silicate Glasses for LED Applications

Luminescence glass is a potential candidate for the light‐emitting diodes (LEDs) applications. Here, we study the structural and optical properties of the Eu‐, Tb‐, and Dy‐doped oxyfluoride silicate glasses for LEDs by means of X‐ray diffraction, photoluminescence spectra, Commission Internationale de L'Eclairage (CIE) chromaticity coordinates, and correlated color temperatures (CCTs). The results show that the white light emission can be achieved in Eu/Tb/Dy codoped oxyfluoride silicate glasses under excitation by near‐ultraviolet light due to the simultaneous generation of blue, green, yellow, and red‐light wavelengths from Tb, Dy, and Eu ions. The optical performances can be tuned by varying the glass composition and excitation wavelength. Furthermore, we observed a remarkable emission spectral change for the Tb³⁺ single‐doped oxyfluoride silicate glasses. The ⁵D₃ emission of Tb³⁺ can be suppressed by introducing B₂O₃ into the glass. The conversion of Eu³⁺ to Eu²⁺ takes place in Eu single‐doped oxyfluoride aluminosilicate glasses. The creation of CaF₂ crystals enhances the conversion efficiency. In addition, energy transfers from Dy³⁺ to Tb³⁺ and Tb³⁺ to Eu³⁺ ions occurred in Eu/Tb/Dy codoped glasses, which can be confirmed by analyzing fluorescence spectra and energy level diagrams.     

A single-phase white-emitting La10(SiO4)6O3：Eu2+/Eu3+ phosphor for near-UV LED-based application

A novel single-phase white-emitting phosphor La₁₀(SiO₄)₆O₃ (LSO): xEu has been synthesized by high-temperature solid-state reaction. Its crystal structure, luminescence properties, fluorescence decay time and oxygen vacancies have been characterized by X-ray diffraction (XRD) and photoluminescence (PL) spectra. XRD result shows a typical oxyapatite structure with the space group of P6₃/m. Characteristic excitation and emission peaks of Eu²⁺ and Eu³⁺ were observed from PL studies. The optimum doping concentration of Eu was found to be 7.5 mol% (x = 0.075). In this work, the lifetimes of Eu³⁺ and Eu²⁺ were considerably longer than those from some references. Under the excitation of different near ultraviolet (n-UV) longer wavelengths (λex = 360, 370, and 380 nm), the white light emission can be realized with the CIE chromaticity coordinates (0.3907, 0.3595), (0.3472, 0.3282), and (0.3504, 0.3062) for the phosphor LSO: 0.075Eu. The chromaticity coordinates of the phosphor were all located in the white region. Therefore, it is suggested that the explored LSO: 0.075Eu phosphor can be a good candidate for white light-emitting diodes (W-LEDs) application.     

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.     

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.     

Photoluminescence properties of NUV light excited Ba(Mg1/3Nb2/3)O3:Eu3+ red phosphor with high color purity

In this work, a new red phosphor with high color purity, Eu³⁺ ions doped Ba(Mg_1/3Nb_2/3)O₃ phosphor has been prepared by wet chemical method. The structure analysis suggests BMN:x%Eu phosphors have a hexagonal phase and Ba²⁺ ions are replaced by Eu³⁺ ions in BMN. Upon excitation of NUV light, the BMN:x%Eu phosphors emit strong red light around 615?nm, derived from the ⁵D₀-⁷F₂ transition of Eu³⁺ ions. The relationship between luminescent properties and structure of BMN:x%Eu was discussed. The Judd-Ofelt intensity parameters (Ω₂, Ω₄) were calculated to analyze the asymmetry of the Eu³⁺ ions site occupancy further, and the quantum efficiency of BMN:3%Eu was found to be 77.26%. In addition, the decay curve indicates the decay time(τ) of BMN:3%Eu is determined to be 1.34?ms and Eu³⁺ ions occupy only one type of site. The CIE chromaticity coordinate (0.656,0.344) of BMN:3%Eu is quite close to the red phosphors standard value (0.670, 0.330), which indicates BMN:x%Eu can be a suitable red phosphor used in NUV-based white LEDs.     

Enhanced luminescent performance for remote LEDs of Ce:YAG phosphor-in-glass film on regular textured glass substrate by using chemical wet-etching

A novel route to modify the luminescent performances of Ce:YAG phosphor-in-glass (PiG) film is proposed in this work, where the yellow-emitting PiG film was placed on regularly nanoscale textured glass substrate through spin coating technique. Different from the mechanical scraping, the regularly textured surface substrate is successfully obtained using hydrofluoric acid solution (HF 48–51%) by chemical wet-etching method and the roughness can be modified by adjusting synthesis time. The textured glass substrate can not only improve the optical uniformity and enhance luminous efficacy by minimizing total internal reflection (TIR), but reinforce the diffuse reflection light to improve visual comfort. The research results show that the quantum yield (QY) and luminous efficacy of the film based w-LEDs on textured glass substrate increase by 22.9% and 11.18%, respectively. These results may bring an inspiring insight to prepare remote phosphor with different spectral performance on regularly textured surface for remote white LEDs.     

Synthesis and luminescent properties of Sr4−xSi3O8Cl4: xEu3+ red phosphor by hydrothermal method

Sr_4‐xSi₃O₈Cl₄:xEu³⁺ (SSOC:Eu³⁺) phosphors were successfully synthesized by hydrothermal method. The crystallization of this phosphor was analyzed by means of X‐ray diffraction patterns. The size and morphology were recorded using SEM patterns of samples. And the PLE and PL spectra were characterized by a PL spectrophotometer. Excited by 394 nm UV light, the intense red emission is recognized in SSOC:Eu³⁺ phosphor and the main emission peak located at 620 nm. The influences of Eu³⁺ concentration, pH value of reaction solution, and charge compensator on PL spectra of SSOC:Eu³⁺ phosphors were investigated. The results revealed that this red phosphor had potential applications for white LEDs.     

Optical properties of zinc borate glasses dispersed with Eu-doped SiAlON for white LED applications

Ca-α-SiAlON:Eu²⁺ oxynitride phosphors are typical luminescent materials with high thermal tolerances. A series of zinc borate glass samples (xZnO-(100-x)B₂O₃; mol%) were prepared for investigating their ability to disperse Ca-α-SiAlON:Eu²⁺ phosphor powders. Phosphor in glass (PiG) was prepared with SiAlON and zinc borate glass through a melting process. In the x = 45–60 range, PiGs could be obtained without the degradation of the SiAlON phosphors. The PiG composed of x = 50 glass exhibited the highest quantum efficiency. The glass structures of the mother glasses were investigated by Raman spectra; there was a decrease in the boroxol ring, and pyroborate and orthoborate were formed, on increasing x. From the XRD and SEM images, it was established that ZnAl₂O₄ was formed around the SiAlON powders in PiGs with x = 50, 55, and 60, respectively. This suggests that the partial crystallizations in the PiGs are effective in enhancing the photoluminescence of the SiAlON phosphors.     

Enhancement of photoluminescence intensity of sintered CaAlSiN3:Eu2+ red phosphor-bismuthate glass composites

Wavelength converters in white light-emitting diodes are usually made by sintering of phosphor-glass powder compacts. An issue is that the sintering process usually results in the reduction of phosphor amount. In the present study, composites containing CaAlSiN₃:Eu²⁺ red phosphor and Bi₂O₃-B₂O₃-ZnO-Sb₂O₅ glass were fabricated by sintering method. Influences of CaAlSiN₃:Eu²⁺ phosphor content (10 vol%–30 vol%) and sintering temperature (410–430°C) on the residual amount of the phosphor phase and the resulting luminescence intensity of the composites were investigated. The change of CaAlSiN₃:Eu²⁺ content due to sintering was analyzed by X-ray diffraction. The interdiffusion between the CaAlSiN₃:Eu²⁺ and glass matrix was examine by scanning electron microscope equipped with energy dispersive X-ray spectrometry. This paper focuses on the change of luminescence intensity after sintering. It was found that although the content of phosphor CaAlSiN₃:Eu²⁺ reduces after sintering; the luminescent intensity of the composites anomalously increases. The optimum luminescence intensity is 14% higher than that of the as-mixed, unfired powder. It is proposed that the incorporation of Bi³⁺ ions from the glass matrix into the phosphor CaAlSiN₃:Eu²⁺ during sintering improves the luminescence ability of the phosphor particles.     

Novel cyan-emitting KBaScSi2O7:Eu2+ phosphors with ultrahigh quantum efficiency and excellent thermal stability for WLEDs

Owing to the conventional phosphor-converted white LEDs (pc-WLEDs) generally suffer from blue-green cavity, thus, developing an appropriate phosphors covering both the blue and green regions in their emission spectra are very urgent. Herein, a novel Sc silicate phosphor, KBaScSi₂O₇:Eu²⁺ (KBSS:Eu²⁺), has been successfully designed and prepared via a solid-state reaction. The crystal structure, luminescent properties, thermal quenching, quantum efficiency as well as its application in UV-pumped WLEDs have been investigated systematically. The KBSS:Eu²⁺ phosphor exhibits a strong and broad excitation band ranging from 290 to 450 nm, and gives a sufficient cyan emission of 488 nm with a full-width half-maximum (FWHM) of 70 nm, which filled the blue-green cavity. Importantly, the optimized KBSS:Eu²⁺ phosphor possesses an ultrahigh quantum efficiency (QE) up to 91.3% and an excellent thermal stability retaining 90% at 423 K with respect to that measured at room temperature. Finally, the as-fabricated UV-based WLEDs device, with only coupled the mixture of KBSS:Eu²⁺ cyan phosphor and CaAlSiN₃:Eu²⁺ red ones to a commercial 365nm UV chip, exhibits a satisfactory color-rendering index (Ra = 88.6), correlated color temperature (CCT = 3770K), and luminous efficiency (LE = 21 lm/W).     

Stable and efficient all-inorganic color converter based on phosphor in tellurite glass for next-generation laser-excited white lighting

Laser lighting is considered as a next-generation high-power lighting due to its high-brightness, directional emission, and quasi-point source. However, thermally stable color converter is an essential requirement for white laser diodes (LDs). Herein, we proposed a stable and efficient phosphor-in-glass (PiG) in which YAG:Ce³⁺ and MFG:Mn⁴⁺ phosphors were embedded into tellurite glass matrixes. The glass matrixes with low-melting temperature and high refractive index were prepared by designing their composition. The luminescence of YAG:Ce³⁺ PiGs was adjusted by controlling phosphor thickness. Aiming to compensate for red emission, multi-color PiGs were realized by stacking MFG:Mn⁴⁺ layers on YAG:Ce³⁺ layer. The phosphor crystals are chemically stable and maintain intact in the glass matrix. Furthermore, white LDs were fabricated by combining the PiGs with blue LDs. As the phosphor thickness increases, the chromaticity of white LDs shifts from cool to warm white, and the white LDs exhibit excellent thermal stability under different excitation powers.