YAG:Ce3+, Gd3+ nano-phosphor for white light emitting diodes

YAG:Ce³⁺, Gd³⁺ nano-phosphors were synthesised by the glycothermal method. The X-ray diffraction measurements showed that the samples can be well-crystallised at 600°C. The transition electron microscope showed that the particles have sizes mostly in the range between 35 and 100?nm. The YAG:Ce nano-phosphor had a wide emission band ranging from blue to yellow with a peak at 532?nm, due to the transition from the lowest 5d band to ²F_7/2, ²F_5/2 states of the Ce³⁺ ion. Red-shift of emission peak wavelength from 532 to 568?nm was achieved doping Gd³⁺ ions into the YAG:Ce³⁺ to substitute some Y³⁺ ions. White light emitting diodes (LEDs) were obtained by combining blue LED chip (InGaN-based 460?nm emitting) with (Y_{2.94? x} Ce_0.06Gd _x )Al₅O₁₂ phosphor. As x has the value of 0.8, an intense white LED with good colour rendering of 86 was obtained.     

Properties of transparent Ce:YAG ceramic phosphors for white LED

Transparent Ce:YAG ceramic phosphors were synthesized from the oxide powder which was produced by co-preparation method of the hydroxides. The Ce:YAG ceramics had a broad emission band peaked at 530 nm due to the 5d → 4f transition of Ce³⁺. The transmittances of the samples obtained were 70-87% at 800 nm. The absorption coefficient and emission intensity of Ce³⁺ were increased with increasing thickness. Under 465 nm LED excitation, the color coordinates of the Ce:YAG ceramics shifted from the blue region to yellow region with increasing sample thickness, passing nearby the theoretical white point in the chromaticity diagram. The highest value of luminous efficacy of the ceramic white LED was 73.5 lm/W.     

Nanocrystalline Y3Al5O12:Ce phosphor-based white light-emitting diodes embedded with CdS:Mn/ZnS core/shell quantum dots

120 nm-sized yellow emitting Y₃Al₅O₁₂:Ce (YAG:Ce) nanocrystalline phosphors and 4.5 nm-sized orange emitting CdS:Mn/ZnS core/shell structured quantum dots (QDs) were prepared by a modified polyol and a reverse micelle chemistry, respectively. To compensate a poor color rendering index (CRI) of YAG:Ce nanophosphor-based white light-emitting diodes (LEDs) due to the lack of red spectral component, CdS:Mn/ZnS QDs were blended into YAG:Ce nanophosphors. Blends of nanophosphors and QDs exhibited the prominent spectral evolution with an increasing content of QDs. A hybrid white LED, which combines a blue LED with the blend of nanophosphor and QDs with a weight ratio of 1:1, was demonstrated with an improved CRI value of 85.     

Preparation and properties of Pr<Superscript>3+</Superscript>/Ce<Superscript>3+</Superscript>:YAG phosphors using triethanolamine as dispersant and pH regulator

Pr³⁺/Ce³⁺:YAG precursors were co-precipitated using triethanolamine as dispersant and pH regulator. The different dosages of triethanolamine (D) vs. the properties of Pr³⁺/Ce³⁺:YAG phosphors were discussed. When D = 0.5 vol%, the pH of titration process was controlled in the range of ～7.94–8.16 to guarantee the uniform distribution of Al, Y, Ce and Pr in the precursors. The relatively higher pH could decrease the loss of Ce and Pr in the precursors and increase the particle size of the obtained powders, which was beneficial to the enhancement of luminescent intensity. Therefore, the precursors directly converted to pure-phase YAG at 900°C, and the phosphors calcined at 1000°C showed the best dispersity due to the dispersion effect of triethanolamine and the most excellent luminescent property. When D ≥ 2 vol%, although pure-phase YAG was detected, the emission intensity of the phosphors decreased due to the decrease of dispersity and purity. Moreover, the co-doped Pr³⁺ enhanced the red emission of Pr³⁺/Ce³⁺:YAG phosphors.     

Novel quantum dots: Water-based CdTeSe/ZnS and YAG hybrid phosphor for white light-emitting diodes

Novel water-based core/shell CdTeSe/ZnS quantum dots (QDs) were synthesized by aqueous method. The CdTeSe/ZnS QDs were investigated by high resolution transmission electron microscopy, energy dispersive spectrometry, UV–vis absorption spectra, and photoluminescence spectrum. The as-prepared QDs capped with ZnS shell were spherical in shape with an excellent quantum yield of 16% and emitted bright yellow light. In addition, the CdTeSe/ZnS QDs can be excited by blue or near-UV region, which is an advantage over wavelength converters for white light-emitting diodes (LEDs). White LEDs based on CdTeSe/ZnS QDs, commercially known as Y₃Al₅O₁₂:Ce³⁺ (YAG:Ce), and hybrid phosphor of CdTeSe/ZnS QDs and YAG:Ce, were fabricated. The luminescent properties of the resultant white LEDs were evaluated. The higher red-component in the emission spectrum from CdTeSe/ZnS QDs increased the color rendering index (CRI) value of the commercial YAG:Ce-based white LEDs, and the hybrid phosphor-based white LED had CIE-1993 color coordinate, color temperature, and CRI values of (0.3125, 0.2806), 7108 K and 83.3, respectively.     

Characterization and biological application of YAG:Ce3+ nanophosphor modified with mercaptopropyl trimethoxy silane

We focus on the inorganic nanophosphor of YAG:Ce³⁺ nanoparticles as an alternative fluorescent probe instead of organic dyes for biological application. YAG:Ce³⁺ nanoparticles have the green emission at 530 nm under the excitation of blue light at 450 nm. Conventional biochemical equipments for organic dyes can be used for YAG:Ce³⁺ nanoparticles. SH groups were introduced by surface modification of YAG:Ce³⁺ nanoparticles with 3-mercaptopropyl trimethoxy silane, and were characterized by X-ray fluorescence analysis, FT-IR, and Ellman method. We demonstrated tagging avidin-immobilized agarose gel beads with biotinylated-YAG:Ce³⁺ nanoparticles, and tagging rabbit IgG-immobilized agarose gel beads with antirabbit IgG-immobilized YAG:Ce³⁺ nanoparticles.     

Ce、Cr∶YAG微晶玻璃的制备及光谱性能研究

目前白光LED在红光波段发射较弱,导致其显色指数偏低,在白光LED用Ce∶YAG微晶玻璃中掺入Cr3+来增强红光波段的发射,从而提高显色指数。通过X射线衍射、荧光光度计、电光源参数测试对样品的晶相、光谱性能及荧光寿命进行了表征。研究了Cr3+对Ce∶YAG微晶玻璃发光性能的影响,并对其增红机理进行了初步的探讨。结果表明基质玻璃在1400℃热处理可析出纯的YAG晶相;Ce∶YAG和Ce、Cr∶YAG微晶玻璃在460nm激发下,在480～650nm产生有效发射,发射光谱中心波长位于530nm;由于Ce3+(2E)-Cr3+(4T)之间的非辐射能量传递,Ce、Cr∶YAG微晶玻璃在688、692和705nm处有红色发射峰,能有效地提高白光LED的显色性能。     

Scintillation properties of Pr3+-doped lutetium and yttrium aluminum garnets: Comparison with Ce3+-doped ones

Scintillation properties of Pr³⁺-doped LuAG and YAG crystals were investigated and compared with those of Ce³⁺-doped ones. The highest L.Y.’s were observed with the longest shaping time 10 μs. They can reach up to ～16,000 ph/MeV or ～23,500 ph/MeV for LuAG:Pr and LuAG:Ce, respectively. Energy resolutions (FWHM) are a bit better with LuAG:Pr than those of LuAG:Ce, e.g. at 662 keV FWHM are around 6% and between 8–12%, respectively. There were observed no large changes in proportionality of Pr³⁺- or Ce³⁺-doped LuAG or YAG crystals but the best proportionality has YAP:Ce crystal. Pr³⁺- or Ce³⁺-doped LuAG crystals exhibit slow decay components in the time range 1.5–3.5 μs while those of YAG ones have shorter decay components between 0.3–1.7 μs.     

Multilayer design of hybrid phosphor film for application in LEDs

Crosslinked polydimethylsiloxane (PDMS) composite coatings containing luminescent micrometer-sized yellow Y₃Al₅O₁₂:Ce³⁺ (YAG:Ce³⁺) particles were prepared by spraying for potential applications in solid-state lighting. Blue light was down converted by phosphor particles to produce white light, yet poor color properties of YAG:Ce³⁺ stemmed from a deficiency of red. When nitride-based red phosphor was simply blended into the system, the electrostatic interaction of negatively charged YAG:Ce³⁺ and positively charged red phosphor particles caused remarkable clustering and heterogeneity in particle dispersion. Consequently, the light is dominantly blue and shifted to cold white. In other case, phosphor particles were sprayed onto the diffused polycarbonate substrate in stacked layers. Coatings with >80% inorganic content by mass with a thickness of 60 μm were subjected to thermal crosslinking, which the presence of the phosphor particles obstructed, presumably due to the hindrance of large phosphor particles in the diffusion of PDMS precursors. The coating of YAG:Ce³⁺ first followed by red phosphor in stacked layers produced better light output and color properties than the coating obtained by spraying the mixture at once. Monte Carlo simulation validated the hypothesis.     

Sol-gel synthesis of yellow-emitting La4Ca(SiO4)3O:Ce phosphors for white-light emitting diodes

Ce³⁺ doped La₄Ca(SiO₄)₃O phosphors with silicate oxyapatite structure were synthesized by the sol-gel process. The X-ray diffraction (XRD) patterns showed that a pure phase was formed when sintering temperature was higher than 1300°C. The optical properties of La₄Ca(SiO₄)₃O:Ce³⁺ phosphors with varying sintering temperature and concentration were investigated by examining their excitation and emission spectroscopy. The phosphors exhibited a broad emission band centered at 550nm which could be attributed to the 5d-4f transition of Ce³⁺ and a stronger excitation peak around 467nm as well as several shoulder bands, nicely matching with the widely applied blue LED chips. Higher emission intensity was observed when firing temperature above 1300°C, due to increasing crystallinity of the powders. When Ce³⁺ concentration was equal to 5 at%, the sample exhibited the optimum excitation and emission efficiency. The results indicate that La₄Ca(SiO₄)₃O:Ce³⁺ is a promising candidate in the application of blue chip excited white light emitting diodes (LEDs).     

Luminescent properties of Ca2BO3Cl:Eu yellow-emitting phosphor for white light-emitting diodes

The Ca₂BO₃Cl:Eu²⁺ phosphor was synthesized by the general high temperature solid-state reaction and an efficient yellow emission under near-ultraviolet and blue excitation was observed. The emission spectrum shows a single intense broad emission band centered at 573 nm, which corresponds to the allowed f-d transition of Eu²⁺. The excitation spectrum is very broad extending from 350 to 500 nm, which is coupled well with the emission of UV LED (350-410 nm) and blue LED (450-470 nm). The measured emission of In-GaN-based Ca₂BO₃Cl:Eu²⁺ LED shows white light to the naked eye with a chromatic coordinate of (0.33, 0.36). The Ca₂BO₃Cl:Eu²⁺ is a very appropriate yellow-emitting phosphor for white LEDs.     

Synthesis and characterization of photoluminescent cerium-doped yttrium aluminum garnet

Powder phosphor yttrium aluminum garnet (YAG), doped with trivalent cerium (Ce³⁺) is synthesized by sol-gel method. The formation of YAG and YAG:Ce (cerium-doped yttrium aluminum garnet) was investigated by means of X-ray diffraction (XRD). Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were also used. The purified crystalline phases of YAG and YAG:Ce were obtained at 1000 °C. The maximum average grain size is about 20-23 nm for undoped samples and 28-34 nm for doped samples. The crystalline YAG:Ce emission shows one peak in the range 480-535 nm with the maximum near 520 nm. Photoluminescence (PL) intensity of 5d → 4f transition of Ce³⁺ increased with increasing annealing temperature. With increasing the concentration of Ce³⁺, the photoluminescence peak shifts towards the red region.     

Luminescence properties and preparation of Lu<Subscript>3</Subscript>Al<Subscript>5</Subscript>O<Subscript>12</Subscript> powder doped with Ce and Pr ions

Lu₃Al₅O₁₂:Ce³⁺ phosphor powder, which exhibits green emission band, was synthesized by the high-temperature solid-state reaction method with a flux BaF₂. X-ray diffraction (XRD), photoluminescence (PL) spectra, and fluorescent lifetime spectra were used to characterize the structure and luminescent properties of the sample. The XRD patterns indicated that when prepared at 1550 °C for 3 h with 4 wt% flux, Lu₃Al₅O₁₂:Ce³⁺ phosphors powder is the garnet cubic crystal system structure. Photoluminescence (PL) spectra showed that the Lu₃Al₅O₁₂:Ce³⁺ phosphor powder can be effectively excited by near ultraviolet and blue light, emitting broad band peaking at 505 nm, which is attributed to ²F_5/2?→?²D_5/2 transition. The self-concentration quenching mechanism of Ce³⁺ is the dipole–dipole interaction. Small amount of Pr³⁺ increased red light emission at 610 nm. Photoluminescence (PL) spectra and fluorescent lifetime spectra indicated that there was an efficient energy transfer process between Ce³⁺ and Pr³⁺.     

Studies on blue and red photoluminescence from Al2O3:Ce:Mncoatings synthesized by spray pyrolysis technique

Al₂O₃:Ce³⁺:Mn²⁺ films deposited by the spray pyrolysis technique show blue and red emissions under ultraviolet light excitation. The blue emission is due to the de-excitation of Ce³⁺ ions from their excited state 5d to the split ground state ²F. The usually weak red emission attributed to 3d→3d de-excitation of Mn²⁺ is enhanced through an efficient energy transfer from Ce³⁺ to Mn²⁺ ions. The quantum efficiency of this transfer is near to 100%. SEM and RBS have been used to analyze the surface morphology and chemical composition of Ce- and Mn-doped Al₂O₃ films. The films were also characterized by the X-ray photoelectron spectroscopy technique, and it was found that a considerable amount of Mn ions remains linked to chlorine while Ce is mostly in an oxidized state.     

Luminescence properties of Ce-Dy codoped aluminium oxide films

Photoluminescence properties of CeCl₃ and DyCl₃ codoped aluminium oxide films deposited by the ultrasonic spray pyrolysis technique were characterized by excitation, emission and decay time spectroscopy. When excited by ultraviolet radiation the films emit a combination of blue and yellow wavelengths through an efficient energy transfer from Ce³⁺ to Dy³⁺ ions (up to around 77%). From spectroscopic data it is inferred that such energy transfer is nonradiative in nature taking place between Ce³⁺ and Dy³⁺ clusters through a short-range interaction mechanism. In the Ce³⁺ doped single film the chromaticity coordinates are in the purplish blue region, whereas that in the cerium and dysprosium codoped films the coordinates move toward the white light emission region.     

High color rendering index white LED based on nano-YAG:Ce3+ phosphor hybrid with CdSe/CdS/ZnS core/shell/shell quantum dots

To improve the poor color rendering index (CRI) of YAG:Ce-based white light-emitting diode (LED) due to the lack of red spectral component, core/shell/shell CdSe/CdS/ZnS quantum dots (QDs) were synthesized and blended into nano-YAG:Ce³⁺ phosphors. Prominent spectral evolution has been achieved by increasing the content of QDs. A white LED combining a blue LED with the blends of nano-YAG phosphors and orange- and red-emission QDs with a weight ratio of 1:1:1 was obtained. This kind of white LED showed excellent white light with luminescent efficiency, color coordinates, CRI and correlated color temperature (CCT) of 82.5?lm/W, (0.3264, 0.3255), 91 and 4580?K, respectively.     

Luminescence and compositional analysis of Y3Al5O12:Ce films fabricated by pulsed-laser deposition

Y_3–xAl₅O₁₂:Ce_x ³⁺ (YAG:Ce³⁺) thin-films were deposited by a pulsed-laser deposition method on quartz substrates using a solid YAG:Ce target. The films were analyzed by X-ray diffraction, scanning electron microscopy, photoluminescence (PL), and energy dispersive X-ray analysis (EDX). The as-deposited films were amorphous and annealing above 900 °C was required for crystallization. PL spectra of annealed films showed a strong and broad emission band around 570 nm and excitations at 342 and 460 nm, all corresponding to transitions between the 4f ¹ ground level to the 5d ¹ excited levels of Ce³⁺ ion. Chemical analysis of films by EDX resulted in nearly the same information as that of the target illustrating excellent stoichiometry replication of the film from the target being sputtered. Electronic Publication     

Ca2SiO4:Ln (Ln = Ce3+, Eu2+, Sm3+) tricolor emission phosphors and their application for near-UV white light-emitting diode

Tricolor emission Ca₂SiO₄:Ln (Ln = Ce³⁺, Eu²⁺, Sm³⁺) phosphors were synthesized by the conventional solid-state reaction method, and their photoluminescence properties were investigated. Ce³⁺-, Eu²⁺-, or Sm³⁺-doped Ca₂SiO₄ phosphors showed typical blue, green, or red luminescence in the CIE1931 chromaticity diagram, respectively. In addition, the luminescence efficiency of the tricolor emission Ca₂SiO₄:Ln (Ln = Ce³⁺, Eu²⁺, Sm³⁺) phosphors was evaluated. A series of white light-emitting diode (LED) prototypes were fabricated by combining near-UV LED chip and the as-prepared tricolor emission phosphors with various ratios in weight. White LED prototypes with tunable correlated color temperature and color-rendering index values were realized by controlling the amount of phosphors. The presented results indicated the potential application of Ca₂SiO₄:Ln (Ln = Ce³⁺, Eu²⁺, Sm³⁺) phosphors in near-UV white LED.     

A novel blue-emitting NaSrPO4:Eu phosphor for near UV based white light-emitting-diodes

A novel blue-emitting phosphor based on a phosphate host matrix, NaSrPO₄:Eu²⁺, was prepared by a conventional solid-state reaction method. The NaSrPO₄:Eu²⁺ phosphor was efficiently excited at wavelengths of 250-450 nm, which is suitable for the emission band of near ultraviolet (n-UV) light-emitting-diode (LED) chips (350-430 nm). The NaSrPO₄:Eu²⁺ phosphor exhibits a strong blue emission peaking at 453 nm and broadly weak green and red emission bands up to 700 nm. The effect of the activated Eu²⁺ concentration on the emission intensity of the NaSrPO₄:Eu²⁺ was also investigated. Here, a phosphor-converted LED (pc-LED) was fabricated and exhibits bright blue emission under a forward bias of 20 mA. All of these characteristics suggest that the NaSrPO₄:Eu²⁺ phosphors could be applicable to n-UV based white LEDs.     

Growth and optical properties of (Yb3−xYx)Al5O12:Ce single crystals

To improve the infrared emission of Yb³⁺ ions doped in the garnet host Y₃Al₅O₁₂ (YAG) single crystal through the energy transfer from Ce³⁺ to Yb³⁺ ions, the 〈1 1 1〉-oriented YAG:Ce³⁺, YAG:Yb³⁺, YAG:(Ce³⁺, Yb³⁺) and Yb₃Al₅O₁₂:Ce³⁺ (YbAG:Ce³⁺) single crystals were grown using the Czochralski Method, respectively. The excitation and emission spectra of these garnet single crystals were characterized. In YAG:Ce³⁺ crystal, the yellow emission of Ce³⁺ ions present, but it was completely extinguished in YAG:(Ce³⁺, Yb³⁺) crystal and YbAG:Ce³⁺ crystal. However, the characteristic absorption bands of Ce³⁺ still existed in the excitation spectrum of Yb³⁺ ions, which showed that the energy absorbed by Ce³⁺ ions can be transferred to Yb³⁺ ions for its infrared emission.