YAG Phosphor Research Articles

Novel red-emitting CsPb1−xTixI3 perovskite QDs@glasses with ambient stability for high efficiency white LEDs and plant growth LEDs

Currently, the application of all-inorganic cesium lead halide perovskite (CsPbX3, X = Cl, Br, I) quantum dots (QDs) is limited due to toxicity of lead and poor ambient stability. In our work, a series of Ti-doped CsPbI3 QDs were successfully prepared in borosilicate glass (SiO2-B2O3-ZnO) by the melt quenching and in situ crystallization technique. The samples showed excellent water/thermal stability, and the tunable emission (650–695 nm) was controlled by different Ti contents and heat treatment temperatures. In particular, the optical properties of CsPb1−xTixI3 QDs@glasses (x ≤ 0.5) are superior to those of pristine CsPbI3 QDs@glass. As a result, the wLED was assembled using red-emitting CsPb1−xTixI3 QDs@glasses and yellow-emitting Ce3+:YAG phosphor under excitation of InGaN blue chip, which demonstrated an outstanding luminous efficiency of 102.44 lm/W, a high color rendering index of 80.6. Particularly, Ti-doped CsPbI3 QDs@glasses with red and far-red light are combined with a blue-chip to assemble an LED device, which exactly satisfies the lighting conditions of plant growth.

Efficiency improvement of Si solar cells by down-shifting Ce3+-doped and down-conversion Ce3+-Yb3+ co-doped YAG phosphors

Down-shifting and down-conversion processes are an effective way to improve the poor response of single crystalline silicon (c-Si) solar cells at shorter wavelength region. The Ce3+-doped YAG possesses a down-shifting (DS) process which converts ultra-violet (UV) and blue light into yellow light whereas Ce3+-Yb3+ co-doped YAG exhibits a down-conversion (DC) process which converts UV and blue light into both yellow as well as near-infrared (NIR) light. In this paper, Ce3+-doped YAG and Ce3+-Yb3+ co-doped YAG phosphors are mixed with ethyl vinyl-acetate and then coated on the top surface of c-Si solar cells by using spin-coating method. The solar cells enhance the energy conversion efficiency from 15.71% to 16.06% (Δη = 2.23%) and 15.96% to 16.63% (Δη = 4.19%) for DS and DC process, respectively. The experimental results demonstrated that these types of phosphors are promising candidates for enhancing the performances of c-Si solar cells in practical application.

Effective Heat Dissipation of QD-Based WLEDs by Stacking QD Film on Heat-Conducting Phosphor-Sapphire Composite

Quantum dots (QDs) are considered as promising color converters in the next-generation white light-emitting diodes (WLEDs) due to their tunable wavelength, high quantum yield, and excellent color rendering. However, the practical applications of QDs and QD composite films are severely hindered by their intrinsical drawbacks of thermal quenching and degradation. In this paper, we proposed an efficient heat dissipation approach to solve this issue by stacking a QD film on a heat-conducting phosphor-sapphire composite (PSC) plate. The PSC plate was prepared by printing and sintering YAG phosphor glass film on a sapphire substrate, which plays the roles of yellow converter and heat sink for the QD film. The luminescent performances of WLEDs were controlled by adjusting the QD contents. The high heat-conducting PSC plate provides an effective heat transfer channel for the QD film, which can sufficiently dissipate the heat to ambient air. Compared with the QD film stacked on the traditional phosphor-in-glass (PiG) and phosphor-in-silicone (PiS), the working temperatures of QD-PSC are reduced by 37 °C and 65 °C at 1000 mA, respectively. The QD-PSC-based WLEDs achieve stable luminescent performances for various operation times. The results demonstrate that the proposed approach can enhance the heat dissipation of QDs and realize stable white lighting.

Red emission generation in Ce3+/Mn2+ co-doping Y3Al5O12 phosphor ceramics for warm white lighting emitting diodes

Y3Al5O12:Ce3+/Mn2+/Si4+ phosphor ceramics were fabricated by solid state reaction. Red emission is obtained, which is attributed to the Mn2+:4T1→6A1 spin-forbidden transition under the excitation of 450 nm via the efficient energy transfer from Ce3+ to Mn2+.The green emission (535 nm) originating from Ce3+ and the orange emission (587 nm) from Mn2+ ions were observed. Mn2+ ions are more inclined to occupy Al3+ octahedral sites and the Si4+ ions locate in the Al3+ tetrahedral sites and their co-doping is for charge compensation. The red emission component in Ce3+/Mn2+/Si4+ doping YAG phosphor ceramics is significant for obtaining warm white lighting upon increasing Mn2+ concentration under 450 nm excitation. White light emitting diodes were successfully constructed by combining the fabricated ceramics with the GaN blue chips.

Thermally stable lead-free phosphor in glass enhancement performance of light emitting diodes application.

A co-sintering method for preparing PIG is proposed, a Ce3+ doped yttrium aluminum garnet (YAG:Ce) phosphor in glass (PIG) slice is fabricated through co-sintering polycrystalline Ce:YAG phosphor, and a new, to the best of our knowledge, homemade matrix glass SiO2-K2O-BaO-B2O3 glass powder is detected to confirm crystal phase by X-ray powder diffractions (XRD) and micromorphology by scanning electron microscope (SEM). The YAG:Ce phosphor particles dispersed in the matrix are vividly observed and their distributions are relatively uniform. The PIG packaged light-emitting diode (LED) sample shows a relatively lower correlated color temperature (CCT) than the conventional phosphor-dispensing LED sample. White light can be achieved in the PIG slice under 465nm LED excitation by controlling the phosphor concentration or thickness. The highest luminous efficacy of the PIG slice packaged white LED is 94.67lm/W at 100mA. Controllable geometrical and optical properties of the YAG:Ce PIG can generate evident improvements in the manufacturing of identical CCTs for high-power white LEDs. The combination of PIG with a blue LED chip of a specific wavelength, if measured before final assembly, enables targeted production of specific CCT white LEDs. PIG technology allows the realization of high stability and thermal conductivity for the phosphor layer. This simple method provides many possibilities for LED packaging, including thin film flip chip and remote phosphor technology.

Samarium doped apatite-type orange-red emitting phosphor Ca5(PO4)2SiO4 with satisfactory thermal properties for n-UV w-LEDs

A novel single-phase Sm3+ activated Ca5(PO4)2SiO4 phosphor was successfully fabricated via a conventional solid-state method, which can be efficiently excited by near ultraviolet (n-UV) light-emitting chips. The crystal structure and luminescence properties were characterized and analyzed systematically by using relevant instruments. The Ca5(PO4)2SiO4:Sm3+ phosphor shows an orange-red emission peaking at 600 nm under the excitation of 403 nm and the optimal doping concentration of Sm3+ is determined to be 0.08. The critical distance of Ca5(PO4)2SiO4:0.08Sm3+ is calculated to be 1.849 nm and concentration quenching mechanism of the Sm3+ in Ca5(PO4)2SiO4 host is ascribed to energy transfer between nearest-neighbor activators. The decay time of Ca5(PO4)2SiO4: 0.08Sm3+ is determined to be 1.1957 ms. In addition, the effect of temperature on the emission intensity was also studied, 72.4% of the initial intensity is still preserved at 250 °C, better thermal stability compared to commercial phosphor YAG:Ce3+ indicates that Ca5(PO4)2SiO4:0.08Sm3+ has excellent thermal stability and active energy is deduced to be 0.130 eV. All the results demonstrate that orange-red emitting Ca5(PO4)2SiO4:0.08Sm3+ phosphor exhibits good luminescent properties. Owing to the excellent thermal quenching luminescence property, Ca5(PO4)2SiO4:0.08Sm3+ phosphor can be applied in n-UV white light emitting diodes and serve as the warm part of white light.

Structural and luminescent characteristics of YAG phosphors synthesized in the radiation field

YAG:Ce, YAGG:Ce ceramics were obtained by sintering the oxide powders in the radiation field. The results of investigations of the structure, composition and luminescence of ceramics are presented. The luminescence characteristics of powders exactly correspond to the phosphors luminescence used in practice obtained by solid-state synthesis methods. It has been established that in the used radiation exposure modes the main factor determining the efficiency of the synthesis is the ionization density.

Effect of strontium co-doping on luminescent properties of Eu-doped YAG phosphors

The change on the luminescent properties due to the Sr2+ co-doping in YAG:Eu3+ phosphors prepared by modified sol-gel methods using glucose as a polymeric agent was investigated. X-ray diffraction (XRD) pattern and Photoluminescence (PL) measurement of YAG:Eu3+/Sr2+ were carried out to characterize their structural and luminescent properties, respectively. The synthesized samples were found to have a single phase cubic structure and the incorporation of dopant and co-dopant did not affect the crystal structure. All samples showed intense red-orange emissions corresponding to the 5D0-7FJ=1,2 Eu3+ transitions and the emission intensity have been little changed by co-doping the Sr2+ ions.

Blue laser diode-pumped Ce:YAG phosphor-coated cylindrical rod-based extended white light source with uniform illumination

We report the development of an extended white light source with uniform illumination using a cylindrical rod coated with Ce-doped YAG phosphor and excited by a blue diode laser. A long cylindrical rod made of transparent acrylic was first ground in order to diffuse laser light uniformly throughout the rod. Ce:YAG phosphor was then coated on the cylindrical rod and a blue color laser beam of 1 W power pumped into it. The laser beam propagates through the entire length of the rod via total internal reflection. This is possible because the laser light is highly directional and coherent with high brightness. To achieve a uniform scattering distribution of blue laser light throughout the length of the cylindrical rod, variations in grinding as well as making a hollow core inside the tube are reported. While propagating through the rod, the blue photons are also scattered out due to the rough scattering surface of the acrylic rod. Some of the blue photons are absorbed by yellow phosphor thus generating yellow color photons and the remaining blue photons are mixed with the yellow light generating white light. Such an extended light source acts as a conventional tubelight of 30 cm length. Due to this extended light source, the illumination is uniform and produces no glare as compared to high brightness laser-based point sources as well as LED-based white light sources. Since the phosphor is coated on the outside of the acrylic rod and laser power is distributed uniformly, the burning of phosphor is completely avoided. The light source was characterized by measuring Commission International de l’Eclairage coordinates and correlated color temperature. This kind of light source is highly useful for general purpose illumination.

Laser-line-driven phosphor-converted extended white light source with uniform illumination.

We report the development of laser-driven extended white light source designed as a light sheet for general illumination. This light sheet is made of two large diffused glass plates. A Ce:YAG phosphor layer was coated and sandwiched between the two diffusing sheets. The blue laser beam was first converted into a uniform laser line using a cylindrical lens, and a laser line was made incident parallel to the edges of the designed light sheet. The blue photons are waveguided inside the glass sheet via total internal reflection and scattered from the diffused surface. Some of the blue photons are absorbed by the Ce:YAG phosphor and down-converted into yellow light of longer wavelength. The white light emanating from the diffuse surface is the combined effect of yellow light with original blue light. The developed light sheet with the combination of laser line generation and total internal reflection is a unique and low-cost method for generating white light with uniform illumination. The details of the development of the light sheet and laser line generation are described. The experimental parameters, such as correlated color temperature and color coordinates, are reported.

Study on TiO2 Coated Y3Al5O12: Ce3+ Phosphor

In this paper,a sol-gel method using tetrabutyltitanate as titanium source was adopted to coat a TiO2layer on the surface of Y3Al5O12:Ce3+ (YAG) phosphor. X-ray diffraction (XRD) and scanning electron microscopy (SEM) were used to analyze the phase and surface morphology of the phosphor. XRD and SEM analysis showed that the surface of YAG phosphor was successfully coated by TiO2.

Nanodefects on Microcrystals of YAG-Based Phosphors

A model of the energy structure of a YAG phosphor microcrystal with nanodefects is presented. A nanodefect is a complex containing all of the elements of a crystal and characteristic defects embedded during synthesis in order to compensate for the differences between charges and elastic stresses.

Ce-doped YAG phosphor powder synthesized via microwave combustion and its application for white LED

Cerium-doped yttrium aluminum garnet (YAG : Ce3 + ) powder phosphor have been extensively studied as phosphors for blue to white light conversion. Y(3 − x)Al5O12 : x Ce3 + (x = 2.0 at. %) were successfully synthesized by microwave-assisted combustion (MW) using the organic fuel urea. A direct conversion from the amorphous phase to the cubic one was obtained at 1050°C for 5 h, together with an increase in the particle size into the range of 50 to 60 nm and decrease in the specific surface area. The as-prepared precursors and powder sintered at 1050°C were characterized for their structure, particle size, morphology, electroluminescence properties, and chromaticity by x-ray diffraction, Brunauer–Emmett–Teller method, Fourier transform infrared spectroscopy, field emission-scanning electron microscopy, transmission electron microscopy, electroluminescence, and standard CIE 1931 chromaticity analysis (CIE) chromaticity diagram, respectively. The results show that the obtained sintered YAG : Ce3 + phosphor powder has spherical-shaped particles and strong yellow emission compared to as-prepared phosphor powder. White light emitting diodes with proper color rendering index, and tunable correlated color temperature properties can be produced by controlling the injection currents and coating thickness of the sample, offering daylight white and neutral white LEDs.

Monochromatic Amber Light Emitting Diode with YAG and CaAlSiN3 Phosphor in Glass for Automotive Applications

Monochromatic Amber Light Emitting Diode with YAG and CaAlSiN3 Phosphor in Glass for Automotive Applications

Синтез, исследование структуры ИАГ и ИАГГ люминофоров в поле радиации

Синтез, исследование структуры ИАГ и ИАГГ люминофоров в поле радиации

Rapid, convenient and low-energy preparation of spherical rare earth doped YAG phosphors by a laser sintering method

Rare earth doped YAG phosphors are prepared rapidly and conveniently by using a laser sintering method with low energy consumption.

Synthesis and enhanced photo/thermal stability of high-luminescent red-emitting CdTe@CaCO3 composite for LED applications

High-luminescent CdTe@CaCO3 composite with strong and stable solid-state red emission (PLQY = ~ 50%) is synthesized via a facile co-precipitation method. The composite particles show rice-like shape with narrow size distribution, non-agglomeration, and smooth surface. A continuous tune of emission wavelength from 690 to 660 nm is achieved by increasing CaCO3 coating proportion. Compared with solid-state CdTe QDs powder, CdTe@CaCO3 composites exhibits a greatly enhancement in emission intensity (280% of initial intensity), remarkably enhancement of photostability (90% after 12 h UV irradiation) and thermal stability (70% at 180 °C). Those improvements are attributed to the effective protection and surface passivation of coated CaCO3 layer on CdTe cores. Using yellow-emitting YAG phosphor and red-emitting CdTe@CaCO3 composite as color-converted layer, the fabricated white LED prototype exhibits high color rendering index (94.3) and low color temperature (3964 K) with proper CIE coordinates (0.3773, 0.3604).

Comparison of the Changes in Luminescence Properties Between Cool White and Warm White LEDs at Varying Temperatures

The changes of luminescence properties in cool white (CW) and warm white (WW) light-emitting diodes (LEDs) in response to operating temperatures are compared in this paper. In addition, the emission spectrum of blue LED chips was characterized under the same experimental conditions for cross-reference analysis. The yellow YAG (Y3Al5O12:Ce <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3+</sup> ) and red nitrididosilicate (Sr2Si5N8:Eu <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2+</sup> ) phosphors were synthesized in-house and packed at different concentration configurations to create LED samples of correlated color temperature 6500 K for CW LEDs and 2700 K for WW LEDs. The emission spectrum measurements showed drastic decrements of light emission intensities for both CW and WW LED samples at elevated temperature. Both CW and WW LED samples tend to have more bluish hue with increasing temperatures. Furthermore, the trend of color rendering index (CRI) changes of CW and WW LEDs has differed, a finding that is not commonly reported in other studies. The CRI of CW LED samples increased, whereas the CRI of WW LED samples decreased at elevated temperature. This is due to different shift directions of peak emission wavelength in yellow Y3Al5O12:Ce <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3+</sup> and red Sr2Si5N8:Eu <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2+</sup> phosphors.

Optical characteristics of Ce,Eu:YAG single crystal grown by Czochralski method

Eu-doped Ce:YAG single crystal (SC) was fabricated by the Czochralski method. The crystal structure, optical and photoelectric property of the constructed w-LED was investigated. The XRD and HRTEM results show that YAG crystal structure has little change when Eu3+, Ce3+ are doped. Absorption spectra and photoluminescence spectra show that the Ce,Eu:YAG single crystal can effectively absorb the 460 nm blue light to form a broadband emission center at 530 nm, decay curves of the crystal show that the energy transfer between Ce3+ and Eu3+ is highly suppressed. Compared with commercial Ce:YAG phosphor, Ce,Eu:YAG exhibits better thermal stability.

Enhancing concentrator monocrystalline Si solar cells by down conversion Ce3+-Yb3+ co-doped YAG phosphors

Down conversion Ce3+-Yb3+ co-doped YAG phosphors are used to enhance concentrator monocrystalline silicon solar cells. The coating of polymethyl methacrylate (PMMA) mixed with the phosphors is deposited on the surface of the solar cells by spin-coating method. It is found that the solar cells with the phosphor coating always have higher conversion efficiency than the bare solar cells under different illumination intensities. This is attributed to the down conversion effect of the phosphors and the reduced reflection (especially in the wavelength range 350–550 nm). The reflection of the light emitted from the phosphor's particles at the air/PMMA interface also contributes to the improvement. The relative growth in the conversion efficiency of the solar cells with the phosphor coatings increases with the illumination intensity from 4.86% under 100 mW cm−2 to 6.04% under 400 mW cm−2 because the increase in the emission from the phosphors is faster than that of the illumination intensity when the illumination intensity increases.