Facile fabrication and luminescence characteristics of Ce:YAG phosphor glass thick films coated on a glass substrate for white LEDs

A pivotal step in providing a better fluorescent material that has high luminous efficacy and excellent thermal stability is to utilize inexpensive phosphors for white light-emitting diodes (W-LEDs). Herein, we demonstrate a feasible tape-casting technique for creating phosphor thick films that consist of Ce: YAG phosphor embedded in relatively low melting point glass frits on an ultrathin glass substrate with controllable film thickness. The glass matrix has ideal densification and interfaces with the glass substrate at a relatively low temperature of 580 °C. Subsequently, the structure and optical properties of the phosphor layer are investigated. In addition, the effect of the phosphor concentration, thick film thickness and location (top or bottom) of the phosphor layer on the photoluminescence properties and chromaticity are also discussed with respect to use in W-LEDs. Significantly, this promising structure has excellent thermal stability and the potential to overcome current limitations of phosphors in high-power W-LEDs. Finally, a high-performance W-LED based on the planar phosphor glass exhibits a luminous efficiency of 108.45 lm W⁻¹, a correlated color temperature of 5408 K and a color rendering index of 76.     

SPS烧结制备新型荧光玻璃材料

以实验室自制SiO2粉体和商用Ce∶YAG荧光粉为玻璃原料,采用放电等离子体烧结（SPS）技术,在1 200℃保温2 min烧结得到有望用于白光LED封装的Ce∶YAG荧光玻璃。用X射线衍射仪（XRD）、荧光光谱（PL）等方法对制备获得的荧光玻璃样品进行表征。结果显示,烧结并没有破坏Ce∶YAG荧光粉的晶体结构,且荧光玻璃主体相仍为玻璃体,该荧光玻璃在460nm具有强吸收峰,在此波长激发下发射出530 nm左右的黄光。研究结果表明,本实验制备的Ce∶YAG荧光玻璃是一种具有重要应用前景的LED封装用新型荧光材料。     

A low sintering temperature glass based on SiO2–P2O5–ZnO–B2O3–R2O system for white LEDs with high color rendering index

A low sintering temperature glass based on the SiO₂–P₂O₅–ZnO–B₂O₃–R₂O (R=K and Na) system was studied as a matrix for embedding phosphors to fabricate color tunable white LEDs. The proposed system, which uses no heavy‐metal elements and can be sintered at 500°C, incorporates thermally weak commercial phosphors such as CaAlSiN₃:Eu²⁺ to produce phosphor‐in‐glasses (PiGs). Changing the mixing ratio of glass to phosphors affected the photo‐luminescence spectra and color coordinates of the PiGs when mounted on a blue LED. The color rendering index (CRI) and color correlated temperature (CCT) of the LEDs were also varied with the mixing ratio, providing color tunable white LEDs. A high CRI, up to 93, as well as highly improved thermal stability were obtained, along with a low sintering temperature compared to other glass systems, suggesting the practical feasibility of the proposed system.     

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.     

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.     

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.     

配料组分对微晶玻璃熔融特性的影响

利用工业废料作为制备微晶玻璃的原料,其配料组成会对高温熔融特性产生明显影响。不同种类粉煤灰在化学组成相差不大的条件下,玻璃相含量高的粉煤灰更有利于配料体系的高温熔融;掺入适量的含W废料能够有效改善微晶玻璃配料体系的高温熔融性能,但掺量不宜太高,当外加掺量为1%时,配料体系的熔融性能能够得到有效的改善。     

Design of the YAG:Ce3+ phosphor in tellurite-germanate glass with high luminous efficiency for laser lighting

The main focus of laser lighting research has been on perfectly combining fluorescent conversion materials with laser light sources to improve luminous efficiency (LE). In this paper, the high refractive index, high transmittance and low sintering temperature of tellurite glass is combined with the thermal stability and mechanical strength of germanate glass，which is innovatively used as a matrix for phosphor-in-glass (PiG). The use of high valent ions as modifiers reduces the diffusion and mobility of ions to reduce the erosion of phosphors and protect the luminescent performance of phosphors. By changing Ge/Te ratio, the glass maintains 80% transmittance, and the refractive index decreases from 1.97 to 1.83 matching that of the YAG phosphor. The increase in GeO₂ improves the thermal stability and mechanical strength of the glass, thereby improving the fluorescence intensity (approximately 1.6%) at 473 K and the luminous flux by up to 12.8%. The best PiG sample had a LE of 230 lm/W and excellent internal quantum efficiency (IQE) of 85.3%, achieving high levels of luminescence. Adding different phosphor contents can achieve the role of adjusting the correlated color temperature (4500–6000 K), and the color coordinates (0.322, 0.330) are close to the ideal white light. These results show that tellurite-germanate glass can be used as a good carrier for fluorescence conversion materials, which brings a new direction for the exploration of glass matrix.     

Eu3+‐doped glass as a color rendering index enhancer in phosphor‐in‐glass

A new method for improving color rendering index (CRI) and low correlated color temperature (CCT) in high‐power white‐light‐emitting diodes (WLEDs) is proposed. We used a configuration of phosphor‐in‐glass (PIG) and studied light output changes with the increment in concentration of yellow‐emitting Y₃Al₅O₁₂:Ce³⁺ (YAG:Ce³⁺) phosphor. The PIG was coupled on the top of blue‐light‐emitting diodes (LED) chip (465 nm). To compensate the lack of red emission in the phosphor, Eu³⁺‐doped tellurium glass with different europium content was employed as a red emitter. The suitable contents of YAG:Ce³⁺ and Eu³⁺ were 7.5 weight percent (wt%) and 3 mol percent (mol%), respectively. The CRI value went from 72 to 82, whereas the CCT was reduced from 24 933 to 6434 K. The proposed structure can improve CCT as well as CRI of WLEDs just by placing a glass on top.     

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.     

Layered Ceramic Phosphors Based on CaAlSiN3:Eu and YAG:Ce for White Light‐Emitting Diodes

To develop warm‐white light‐emitting diodes via conversion phosphors, blue light‐emitting diodes are generally combined with mixtures of green and red‐emitting phosphor powders. Generally, the phosphors are provided by resin embedded particle dispersions. Such resin‐based solutions cause several drawbacks with respect to LED lifetime and quality. Therefore, it has been investigated whether the red‐emitting nitride phosphor CaAlSiN₃:Eu and the green‐emitting oxidic phosphor YAG:Ce can be cofired to layered ceramic composites. The shrinkage behavior and the composition of the interface in dependence of sintering temperature and the effect of interdiffusion processes at the interface on the luminescence properties were investigated. The formation of secondary phases at the interface in the cofired structures was found to limit the phosphor functionality for the nitride‐based CaAlSiN₃:Eu in such composite ceramics. To counteract this, sacrificial interlayers were introduced to produce multilayered ceramics comprising CaAlSiN₃:Eu and YAG:Ce for LED lighting applications. It is shown for the first time, that it is possible to sinter layered CaAlSiN₃:Eu and YAG:Ce composite ceramics in a pressureless process at moderate sintering temperatures if one uses thin‐film passivated interfaces to reduce luminescence‐disturbing diffusion phenomena. These results demonstrate that diffusion barriers can be suitable means to obtain layered ceramic composites comprising CaAlSiN₃:Eu and YAG:Ce in a pressureless sintering process with good optical properties.     

Erosion behavior and luminescence properties of Y3Al5O12:Ce3+-embedded calcium bismuth borate glass-ceramics for WLEDs

Current white light emitting diodes (WLEDs) have poor thermal stability and lack red-light, which restrict their applications in high-power and high-color-rendering-index solid-state lighting. YAG glass-ceramics provide an efficient way to resolve these problems. Herein, novel YAG-embedded calcium bismuth borate glass-ceramics (YAG-GCs) with Eu³⁺ doping were prepared using a rapid melt quenching technique. The precursor glass exhibits superior YAG refractive index matching and high transmittance. Differential scanning calorimeter simulations verify YAG particles react with the precursor glass. The degree of YAG erosion is slight but monotonously increases with the co-sintering temperature from 640 to 700°C. The erosion products probably contain YAB (Al₃Y(BO₃)₄), Al₃Eu(BO₃)₄, Bi₂₄B₂O₃₉, and Ca₁₂Al₁₄O₃₃ phases, and the Bi ion valence state is maintained during the reaction process. The energy transfer from Ce³⁺ to Eu³⁺ is suppressed. The YAG-GC PL intensities monotonously increase as the co-sintering temperature decrease from 640 to 700°C and the YAG content increase from 2.5 to 7 wt.%. The optical parameters of a WLEDs packed by YAG-GCs and blue chips are a luminous efficiency of 105.3 lm/W, correlated color temperature of 3940 K and color rendering index of 70.1. The as-prepared YAG-GCs are promising candidates for high-power, warm WLEDs due to their superior thermal stability, high quantum efficiency, and low cost.     

Glass-Ceramics and Solid-State Lighting

Yttrium aluminum garnet (YAG) doped with Ce³⁺ ion is known as an excellent phosphor for light-emitting diode (LED), usually used as a powder form dispersed in organic resins. We have developed translucent glass-ceramics (GC) of YAG: Ce³⁺ microcrystals in 2004. The GC sheet with half millimeter thick can work efficiently to make identical emission spectra with conventional white LED when combined with a blue LED. This report reviews the development history of the GC materials and impact for all inorganic solution for solid-state lighting.     

Zero-thermal-quenching of LiAl5O8: Eu2+, Mn2+ phosphors by energy transfer and defects engineering

The photoluminescence behavior of inorganic phosphors is generally influenced by thermal stability, which determines the luminescence efficiency of the corresponding devices. Here, a series of Eu²⁺, Mn²⁺ co-doped LiAl₅O₈ blue-green-emitting phosphors with thermal robust are successfully fabricated. The concentration-dependent emission spectra and the decay curves of the as-obtained LiAl₅O₈: Eu²⁺, Mn²⁺ samples manifest the occurrence of the energy transfer from Eu²⁺ to Mn²⁺ ions via dipole-dipole interaction, and the corresponding emitted colors are gradually modulated from blue to green under the excitation of 310 nm. Moreover, the zero-thermal-quenching luminescence is observed when the operation temperature is up to 423 K, which is attributed to the energy release from the trapping centers to emitting centers (Eu²⁺ and Mn²⁺) at high temperature. Furthermore, a warm white light-emitting diodes (WLEDs) device with correlated color temperature of 5061 K, a color rendering index of 80.6 and long-term stability is fabricated by combining UV LED chip (λ_ex = 310 nm), as-obtained LiAl₅O₈: Eu²⁺, Mn²⁺ phosphor, commercially available red phosphor and green phosphor. These results prove the potential application of the as-obtained LiAl₅O₈: Eu²⁺, Mn²⁺ phosphor for UV-pumped WLEDs devices.     

Thermal stability and luminescence of novel garnet-type yafsoanite Ca3Zn3(TeO6)2:Sm3+ phosphors for white LEDs

In this study, novel garnet-type yafsoanite tellurate Ca₃Zn₃(TeO₆)₂:Sm³⁺ phosphors are successfully synthesized using the traditional high-temperature solid-state reaction. The phase purity of the obtained phosphors is analyzed by X-ray diffraction and Rietveld refinement studies. Morphological variations are also observed with the different concentrations of Sm³⁺ ions substitution, which is analyzed using Scanning Electron Microscopy (SEM). The photoluminescent properties of the phosphors are systematically investigated. Results show that the samples display the strongest emission peak at 612 nm under the near-ultraviolet (n-UV) 409 nm excitation. This peak can be ascribed to the ⁴G_5/2 → ⁶H_7/2 transition of Sm³⁺. The Ca₃Zn₃(TeO₆)₂:Sm³⁺ phosphor shows a high color purity, exhibits excellent thermal stability and good color drifting resistance. Furthermore, red and white light-emitting diodes have been successfully prepared. The white light-emitting diodes (w-LEDs) demonstrates a high color rendering index (CRI, R_a) and low correlated color temperature (CCT). This study introduces a new orange-red-emitting phosphor and discusses its application in herb-growth w-LEDs.     

珍珠岩制备单一α-堇青石微晶玻璃及其性能

以珍珠岩为主要原料制备了单相α-堇青石微晶玻璃.采用DSC、XRD及FESEM分别研究了微晶玻璃的烧结和晶化行为、晶相组成及显微结构.探讨了烧结温度和SiO2含量对微晶玻璃晶相、显微结构及性能的影响.结果表明,随着烧结温度升高,微晶玻璃中μ-堇青石逐渐减少并转变成α-堇青石,微晶玻璃的孔隙率减少.随着SiO2含量升高,α-堇青石晶相析出温度先降低后增高,微晶玻璃的密度及抗折强度先增大后减小,介电性能变差.当Mg∶Al∶Si=2∶2∶5.95时经900 ℃烧结6 h制得单一α-堇青石微晶玻璃,并具有高抗折强度(116 MPa),低介电常数(5.72,10 MHz),低介电损耗(0.0059,10 MHz),与Si相匹配的热膨胀系数(2.91×10-6 K-1),可以用作低温共烧陶瓷材料.     

铁对R_2O-CaO-gO-Al_2O_3-SiO_2系玻璃微晶化的影响

就石材锯切粉在微晶玻璃中应用的主要问题—铁对析晶的影响展开研究。结果表明,少量铁(＜2mol%)的引入,可能引起析晶参数的升高,但外加铁含量超过2mol%时均可降低析晶参数,并使起始析晶至析晶峰的温度区间(Tp-Tg)变窄；外加铁量＜2mol%时,不同含铁量配方的(Tp-Tg)区间重叠显著,可以采用同一温度晶化处理；配方含铁与否对主晶相没有明显影响,但影响玻璃的析晶能力,铁含量＜2mol%时,使玻璃体析晶能力增加,接近或大于3mol%时,玻璃析晶能力降低；微粉制备微晶玻璃可以大幅度缩短晶化时间。     

铁对R2O-CaO-MgO-Al2O3-SiO2系玻璃微晶化的影响

就石材锯切粉在微晶玻璃中应用的主要问题-铁对析晶的影响展开研究。结果表明，少量铁（〈2mol％）的引入，可能引起析晶参数的升高，但外加铁含量超过2mol％时均可降低析晶参数，并使起始析晶至析晶峰的温度区间（Tp-Tg）变窄；外加铁量〈2mol％时，不同含铁量配方的（Tp—Tg）区间重叠显著，可以采用同一温度晶化处理；配方含铁与否对主晶相没有明显影响，但影响玻璃的析晶能力，铁含量〈2mol％时，使玻璃体析晶能力增加，接近或大于3mol％时，玻璃析晶能力降低；微粉制备微晶玻璃可以大幅度缩短晶化时间。     

Continuously tunable broadband emission of Mn2+‐doped low‐melting point Sn–F–P–O glasses for warm white light‐emitting diodes

Tin fluorophosphate (TFP) glass, which can be used to manufacture a phosphor‐in‐glass (PiG) for achieving high‐power white light‐emitting diodes (w‐LEDs), has attracted a great deal of attention because of its low‐melting point. Mn²⁺‐doped ultralow glass transition temperature (~122°C) Sn–F–P–O glasses were prepared to achieve broadband visible light emission from 390 to 720 nm. By controlling the concentration of MnO, the emission color of the TFP glass can be adjusted from blue/cool white to warm white/red. In particular, 0.2 mol% MnO‐doped TFP glass, which yields bright and warm white light and has ultralow glass transition temperature and thermal stability, has a promising application prospect in the field of high‐power w‐LEDs.     

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.