YAG Particles Research Articles

Phosphor Ceramic Composite for Tunable Warm White Light.

Composite phosphor ceramics for warm white LED lighting were fabricated with K2SiF6:Mn4+ (KSF) as both a narrowband red phosphor and a translucent matrix in which yellow-emitting Y3Al5O12:Ce3+ (YAG) particles were dispersed. The emission spectra of these composites under blue LED excitation were studied as a function of YAG loading and thickness. Warm white light with a color temperature of 2716 K, a high CRI of 92.6, and an R9 of 77.6 was achieved. A modest improvement in the thermal conductivity of the KSF ceramic of up to 9% was observed with the addition of YAG particles. In addition, a simple model was developed for predicting the emission spectra based on several parameters of the composite ceramics and validated with the experimental results. The emission spectrum can be tuned by varying the dopant concentrations, thickness, YAG loading, and YAG particle size. This work demonstrates the utility of KSF/YAG composite phosphor ceramics as a means of producing warm white light, which are potentially suitable for higher-drive applications due to their increased thermal conductivity and reduced droop compared with silicone-dispersed phosphor powders.

Microstructure and phase formation of atmospheric plasma sprayed YAG coatings

In this study, a YAG coating was prepared on a titanium alloy (Ti60) utilizing the Atmospheric Plasma Spraying (APS) technique. SEM, XRD, and TEM were employed to analyze the microscopic morphology and phase composition of the coating. The results show that the APS YAG coating is complete, compact and well-bonded. The coating is primarily amorphous and composed of YAG, YAP, YAM and other Y-rich composition. The formation of Y-rich components is caused by the loss of Al2O3.However, due to continuous heating of the plasma plume, the surface of the coating exhibits higher crystallinity. The main crystalline phases in the coating are YAG, YAP and YAM. Besides the plasma plume, recrystallization of melted YAG particles and un-melted portion of YAG particles contribute to other crystalline phases in the coating. Furthermore, the formation of Y-rich stringer structure in the coating is also associated with droplet splashing.

Nd3+:YAG microspheres powders prepared by spray pyrolysis: Synthesis, characterization and random laser application

Nd3+:YAG crystals have been used to develop photonic devices since the 1960s. Its unique properties, which stem from the combination of the YAG structure with lanthanide ions, have made it the most widely employed material in commercial solid-state lasers. This work reports the synthesis of dense Nd3+:YAG particles prepared by spray pyrolysis. During the synthesis, no clusters emerged, and the particles did not coalesce even after thermal treatment at 1100 °C. All characterization confirmed that the YAG phase was obtained as a spherical micro- and sub-micrometric material. In addition, the photoluminescence spectra showed the expected spectroscopic profile of Nd3+ replacing Y3+ at the dodecahedral sites. The presence of high Nd3+ concentration was exploited as a simultaneous gain and scatter medium for random laser application. The spray pyrolysis methodology described could be easily scaled up for a pilot setup or industrial production. Further applications as sensors or superluminescent sources can be envisaged.

A new BaAl2O4-YAG: Ce composite ceramic phosphor for white LEDs and LDs lighting

A new BaAl2O4-YAG: Ce composite ceramic phosphor (CCP) was prepared and studied as the color conversion materials for high-efficiency white LEDs/LDs lighting. It was discovered that the grain growth of YAG can be remarkably restrained by the introduction of BaAl2O4 second phase, which brought about a small and uniform distribution of YAG particles. 10 wt% BaAl2O4-YAG: Ce CCP presents excellent luminescent performances with a maximum luminous efficacy (LE) of 150 lm/W under the excitation of blue LEDs. When excited by blue LDs with an input power of 13.44 W, 20 wt% BaAl2O4-YAG: Ce CCP shows no luminescent saturation and its maximum luminous flux (LF) is up to 479 lm. Compared to pure YAG: Ce CCPs, BaAl2O4-YAG: Ce CCP has better luminescent characters, which manifests its great application potential in high brightness white LEDs/ LDs lighting.

Up-Converting Lanthanide-Doped YAG Nanospheres

The development of lanthanide-doped Y3Al5O12 (Ln:YAG) garnet nanostructures is a hot topic in the field of inorganic nanophosphors due to the current interest in developing small nanoparticles for solid-state lighting (SSL), displays, lasers and scintillation applications. In this study, we report the preparation of homogeneous Ln:YAG (Ln: Ho/Yb ions) nanospheres through a combined two-steps coprecipitation-solvothermal synthesis at low temperature. The crystal growth takes place in ethylene glycol, which is an inexpensive, non-toxic and easily available solvent. Monodisperse and crystalline spherical YAG particles of 80 nm in diameter were obtained. Furthermore, the protocol can be extended to other compositions (Tb/Yb, Tm/Yb…) to explore different luminescent properties, without affecting the morphology of the material, indicating the robustness and practical utility of the reported methodology. Thermal treatment of the nanogarnets at 1200oC is necessary for making materials optically active upon both UV and NIR excitation. The spherical morphology of annealed samples is preserved, what helps their further dispersion in solvents, barbotines, inks or printing vehicles. The lanthanide-doped nanogarnets exhibited the characteristic blue, green and red emissions from lanthanide upconversion photoluminescence (UCPL) upon NIR excitation. The UCPL mechanism was studied and CIE chromate coordinates were obtained. These nanogarnets were further evaluated as functional ceramic phosphors by incorporating them into commercial glazes. The materials exhibited an exceptional chemical stability in a harsh medium such as a fused glaze. Consequently, the visible emissions of the nanoparticles were transferred to the whole glass matrix, thus providing a functional glaze that emits intense blue and green light upon NIR excitation. These luminescent nanogarnets have promising applications in smart enamels, but can also be useful for lighting displays (white LEDs…), smart paintings or plastics, and anti-counterfeiting systems.

Synthesis, structural and optical characterization of Nd: YAG powders via flame spray pyrolysis

In this study, undoped Y3Al5O12 (YAG) and neodymium (Nd3+) doped (Nd: YAG) powders were synthesized by Flame Spray Pyrolysis (FSP) for the first time in literature. The synthesized powders were investigated about structural, morphological, elemental and optical properties by using Thermogravimetric - Differential Thermal Analysis (DTA-TG), X-ray diffraction (XRD), Scanning Electron Microscopy (SEM), X-ray Photoelectron Spectroscopy (XPS), Fourier Transformed Infrared Spectroscopy (FTIR), and photoluminescence spectroscopy (PL). The particle size range of undoped and Nd doped YAG powders produced by the FSP method was determined around 200–1100 nm. After calcination at 1000 °C, cubic YAG crystalline phases were successfully observed. The luminescence results as excitation, emission, and upconversion properties have been investigated for both undoped YAG (YG) and Nd3+ doped YAG with different dopant ratios as 1% (YG1), 3% (YG3) and %5 (YG5). When synthesized powders excited at 460 nm, the emission maxima observed at 540 nm and 808 nm. All YAG powders yielded bi-exponential decay curves. The highest decay time value was 1% Nd: YAG particle at 277 μs. Furthermore, these powders exhibited upconversion luminescence at lower wavelengths and higher energies when excited at 808 nm.

Facile preparation and optical properties of Te/Pb-free Y3Al5O12:Ce3+ phosphor-in-glass via a screen-printing route for high-power WLEDs

The applications in high-power fields of white light-emitting diodes (WLEDs) are restricted due to their poor thermal stability. Transparent Y3Al5O12:Ce3+ phosphor-in-glass (YAG-PiG) provides an efficient way to resolve this problem. In this work, novel transparent Te/Pb-free YAG-PiGs are successfully prepared via a facile screen-printing route. It is revealed that 5 mol% Eu2O3 optimizes the concentration in substrate glass. Slight erosion of YAG particles occurs in the as-prepared samples. With increasing YAG concentration and film thickness, the intensities of photoluminescence spectra of YAG-PiGs increase. The energy transfer from Eu3+ to Ce3+ is greatly suppressed. Superior thermal stability and high quantum efficiency are obtained. The optimal optical performance values in terms of a luminous efficiency of 117.2 lm/W, a correlated color temperature of 5859 K and a color rendering index of 77.2 are achieved in YAG-PiGs. All of the results reveal that the as-prepared YAG-PiGs are promising candidates for high-power WLEDs.

Formation mechanisms of Y–Al–O complex oxides in 9Cr-ODS steels with Al addition

For the Al-alloyed 9Cr-ODS steels consolidated by spark plasma sintering and annealed at 800 °C, the Y–Al–O oxides, interface structure and orientation relationships between the oxides and the matrix are studied by high-resolution transmission electron microscope technique. It is found that the spark plasma sintering can serve as a useful and effective tool to investigate the transition states in complex oxide formation. Monoclinic Y4Al2O9 (YAM), orthorhombic YAlO3 (YAP), cubic Y3Al5O12 (YAG) and Y2O3 nanoparticles are identified. Both YAM and YAG can directly precipitate from the Y2O3 particles. One individual Y2O3 particle will produce several YAM particles, while only one YAG particle can be formed within one Y2O3 particle. The majority of identified Y–Al–O oxides exhibit partially coherent interfaces with the matrix, and multiple orientation relationships are revealed.

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

AbstractCurrent 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.

Effect of the Synthesis Method on the Properties of Ultrafine YAG Powder

YAG materials has a number of unique properties, the application is very extensive. In this paper, the superfine YAG powder materials were prepared by co-precipitation method and hydrothermal precipitation method. The influence of synthesis process on the morphology of the powder was investigated. The results showed that the precursor powder prepared via the co-precipitation method is mainly from amorphous to crystalline transition with the increasing calcination temperature, the precursor agglomeration is more serious, In the process of increasing the calcination temperature, the dispersibility of the roasted powder is greatly improved, which is favorable for the growth of the crystal grains, so that the particle size of the powder is gradually increased, the YAG precursor prepared by the co-precipitation method is transformed into YAG crystals, the phase transition occurs mainly between 900 and 1100°C. When the molar ratio of salt to alkali is Y3+: OH-=1: 8 via the hydrothermal reaction, the YAG particles with homogeneous morphology can be obtained. When the molar ratio of salt and alkali is increased continuously, the morphology of YAG particles is not obviously changed. The co-precipitation method is easy to control the particle size, the hydrothermal method is easy to control the particle morphology.

Rapid synthesis of nanocrystalline YAG via microwave‐assisted solvothermal process

AbstractA rapid synthesis procedure for the preparation of nanocrystalline yttrium aluminium garnet (nYAG) particles has been developed, for the first time, using the combination of subcritical conditions and microwave irradiation. It is believed that the use of butanediol delayed the onset of pressure rise due to its low partial pressure, while the microwaves facilitated a selective crystallization of nanocrystalline YAG particles in the solvent medium. This methodology was found to encourage rapid bulk nucleation with minimal particle growth or agglomeration of nYAG particles. The resultant powder characteristics, examined using XRD and TEM analyses, revealed that a narrow window of pressure and temperature conditions needed to be maintained to achieve spherical particles in the size range 60‐80 nm without any intermediate phases being formed. The STEM/EDX and FTIR results obtained suggested that the nucleated YAG particles were masked by carbon clouds until they were completely crystallized into single phase YAG particles; this allowed them to be dispersed in water with little agglomeration.

Structural, morphological and electrical properties of alumina/YAG composites as solid electrolyte for IT - SOFC

Alumina/YAG composites (AYX_t) with high relative density (99.2 %TD) were successfully obtained by mixing commercial alumina powder with different volume fractions of yttrium aluminium garnet (Y3Al5O12-YAG; 7, 14, 21 and 28). YAG was synthetized by nitrate glycine reaction in the form of precursor powder. Polycrystalline YAG powder was obtained by calcination at 950?C for 2 h. Additionally, obtained compositions were characterized by XRD, SEM, EDX and electrochemical impedance spectroscopy. By XRPD analysis was found that the particle size of YAG powders lies in the nanometric range (being lower than 35 nm). By SEM microphotographs of composites were confirmed the formation of a conductive path consisting from mutually interconnected YAG particles. This was confirmed by the electrochemical impedance spectroscopy. The highest electrical conductivity of grain (?g) and grain boundary (?gb) at 700?C amounted to 2.22?10-2 ?-1cm-1and 9.44?10-3 ?-1cm-1, respectively, was measured in the composite containing 21 vol% of YAG.

Erosion mechanism of YAG:Ce3+ phosphor in bismuth borate glasses

The poor thermal stability of current commercial white light emitting diodes (WLED) fabricated using a blue chip, a yellow YAG:Ce3+ phosphor (YAG) and resins, restricts their application in fields where long service time and high power lighting systems are required. Incorporating YAG into glass offers a possible way to resolve the problem by removing the organic resins in LED encapsulation. In the present study, YAG glass-ceramics with bismuth borate glass matrices were prepared using a rapid melt quenching technique. The YAG erosion mechanism was investigated for the first time in various glass matrix compositions at different co-sintering temperatures. The results demonstrate that neither B2O3 nor Bi2O3 individually erodes YAG particles, but the mixtures of B2O3 and Bi2O3 binary glass systems react with YAG and dissolve it almost completely or generate YAl3(BO3)4 (abbreviated as YAB), and they even erode as-produced YAB again under certain conditions. The production of YAB particles increases with the increase of the nBi/nB ratio at a lower temperature (680°C), while it first increases and then decreases at a higher temperature (800°C). The maximum production of YAB can be obtained at the co-sintering temperature of 680°C with an nBi/nB ratio of 55:45 or at 760°C with an nBi/nB ratio of 35:65. The intermediate Bi4B2O9 phase is found during the transformation of YAG into YAB. A simple but efficient approach is proposed to prevent YAG erosion and increase the luminous properties of YAG glass ceramics to a great extent by simply adding Ca2+ into bismuth borate glass matrices. The degree of YAG erosion decreases with increasing Ca2+ concentration until an impurity phase appears when the Ca2+ concentration exceeds 20mol%. The combination of good white light emission and suitable quantum efficiency as well as higher thermal stability makes the as-prepared YAG glass-ceramics equipped with a blue chip a possible alternative to commercial WLED.

Synthesis and sintering of submicron Nd:YAG particles prepared from carbonate precursors

Using high-temperature X-ray diffraction, differential scanning calorimetry, and electron microscopy, we have studied the formation of yttrium aluminates and Nd:YAG (YAG) activated garnet nanoparticles during the thermal decomposition of a poorly crystallized carbonate precursor prepared in the NH4Al(OH)2CO3–(Y,Nd)(ОН)CO3 nanosystem and the development of the morphological structure of powders during heating to a temperature of 1350°C. The results demonstrate that heat treatment in the temperature range 850–950°C leads to the formation of metastable nonstoichiometric YAlO3 with a garnet-like structure, which reacts with Al2O3 at a temperature of 1000°C to form YAG. The cubic cell parameter a and X-ray density of YAG crystals with the composition Y2.97Nd0.03Al5O12 synthesized at 1200°C are 1.2009 nm and 4.565 g/cm3, respectively, and the average particle size is 108 nm. Using carbonate route, we prepared transparent Nd:YAG ceramics with a relative density of 99.7%, X-ray density of 4.562 g/cm3, and crystallite size in the range 1–7 μm.

Up-converted ultraviolet luminescence of Er3+:BaGd2ZnO5 phosphors for healthy illumination

Moderate level of exposure to the solar irradiation containing UV component is essential for health care. To incorporate the UV-emitting phosphors into the commercial YAG-based white light-emitting diode introduces the possibilities of healthy illumination to individuals’ daily lives. 1 mol.% Er3+-doped BaGd2ZnO5 (BGZ) particles were synthesized via sol-gel method and efficient up-converted luminescence peaked at 380 nm was detected under 480 nm excitation. The mixed phosphors with varied mass ratio of Er3+:BGZ and Ce3+:YAG particles were encapsulated to form LEDs. The study of the LEDs indicated that the introduction of BGZ component favored the enhancement of color-rendering index and the neutralization of the white light emitting. The WLED with the BGZ/YAG ratio of 8:2 was recommendable for its excellent overall white light luminous performances and UV intensity of 84.55 mW/cm2. The UV illumination dose of the WLEDs with mixed YAG and BGZ was controllable by adjusting the ratio, the illumination distance and the illumination time. Er3+:BGZ phosphors are promising UVemitting phosphors for healthy indoor illumination.

Organically modified clays as rheology modifiers and dispersing agents for epoxy packing of white LED

We develop a new class of polyetheramine-modified organoclays that enable the homogenous dispersion of inorganic phosphorescent phosphor powder, yttrium aluminum garnet Y3Al5O12 (YAG), in epoxy, which can then be used for packing of light-emitting diode (LED) devices. The organoclays are prepared from the ionic exchange reaction of sodium montmorillonite (Na+-MMT) with poly(oxypropylene) (POP) diamines of sufficiently high molecular weight, which are found to be effective for homogenizing YAG in the two-component epoxy system involving an anhydride curing agent and an aliphatic epoxy resin. By adding the POP-diamine-based organoclays, the viscosity of the anhydride/epoxy resins is greatly enhanced and the resin shows a non-Newtonian shear-thinning behavior. Because of the high viscosity that retards the molecular motion, the micrometer-scaled YAG particles can remain dispersed in the resins for a fairly long time without precipitation during the curing process. We investigate the rheological properties of the organoclays as the thickening agent and applied the organoclays to fabricate YAG particle-dispersed epoxy for packing of blue light LED that mixes the yellow light of the well-dispersed YAG particles to form uniform white illumination.

Synthesis of highly porous Al2O3-YAG composite ceramics

Al2O3-YAG composite was obtained by sintering of porous Al2O3 preforms infiltrated with water solution of aluminium nitrate nonahydrate, Al(NO3)3?9H2O and yttrium nitrate hexahydrate, Y(NO3)3?6H2O. Al2O3 preforms with porosity varying from 26 to 50% were obtained after sintering at temperature ranging from 1100 to 1500?C. Sintering of the infiltrated Al2O3 preforms led to formation of YAG particles due to reaction between Y2O3 and Al2O3 at high temperature. It was found that variation of porosity of alumina preforms and sintering temperature is an effective way to fabricate Al2O3-YAG composite with an unusual combination of properties. Open porosity was in the range 15-35%, specific surface was 0.6-6.1 m2/g, pore size was 150-900 nm whereas compressive strength was from 50 to 250 MPa. The effect of sintering temperature on YAG formation and phase composition were investigated using X-ray diffractometry whereas microstructure of the composite was analysed by scanning electron microscopy.

Solvothermal nanoYAG synthesis: Mechanism and particle growth kinetics

NanoYAG particles with spherical morphology have been synthesised using a solvothermal method; a structure sensitive reaction, where the chemical reaction and the particle growth kinetics are interdependent. It has been observed that the primary YAG particles agglomerated into ∼30nm clusters via a self-assembled Ostwald ripening process along (211) planes, separated by a distance of ∼0.49nm, at 270°C and 2.0MPa for 2h. These nanoclusters coalesced into single nanoparticles of ∼30nm in size and exhibited a smaller inter planar distance of ∼0.26nm, corresponding to the (420) planes, when synthesized at 300°C and 8.5MPa for 2h. in addition, the solvent 1,4-butanediol transformed into 1,4-diacetoxybutane, this will have undergone esterification by reacting with the terminal acetate groups cleaved from the precursor, yttrium acetate. The proposed mechanism based on the analytical evidence suggests that a complete dissolution of precursors facilitated the structural re-arrangement of atoms within the planes and lead to a significantly higher degree of crystallinity. Moreover, once the particles with (420) planes had formed, they were no longer involved in facile coalescence along their preferential planes due to their lower interfacial energy compared to the (211) planes. This led to control of the particle morphology and with little agglomeration occurring in the final nanopowder.

The microstructure and mechanical properties of Al-containing 9Cr ODS ferritic alloy

In this study, a 9Cr oxide-dispersion strengthened (ODS) alloy with additional corrosion resistant element Al was fabricated by mechanical alloying (MA) and hot pressing (HP) to explore the impact of Al on the microstructure and mechanical property of a 9Cr ODS alloy. It is found that the Al completely dissolved into the Fe–Cr matrix after milling for 30 h. The minor phases in the Al-containing 9Cr ODS ferritic alloy were investigated by a high-energy X-ray, and were identified to be orthorhombic-YAlO3 (YAP), bcc-Y3Al5O12 (YAG), monoclinic-Al2Y4O9 (YAM), and hexagonal-YAlO3 (YAH). These phases were further confirmed by selected area diffraction pattern (SADP), energy dispersive spectroscopy (EDS), and high resolution transmission electron microscopy (HRTEM). In addition, their volume fractions were also calculated from the integrated intensities. According to the analysis of the particles and their formation sequences, the larger particles (greater than 100 nm) are identified as mainly YAG and Al2O3 particles, while the particles with small size (less than 30 nm) are likely primarily YAM, YAH, and YAP particles. The yielding strength (YS) and ultimate tensile strength (UTS) at RT are 563 MPa and 744 MPa, respectively, while the YS and UTS at 700 °C are 245 MPa and 276 MPa, respectively. Although the addition Al in ODS alloys decreases the strength at RT, the values at high temperature are similar to those obtained for 9Cr ODS alloys strengthened by fine Y–Ti–O particles.

Comprehensive study of photoluminescence and cathodoluminescence of YAG:Eu3+ nano- and microceramics

The nanosized YAG particles doped with Eu3+ as the luminescent probe, were prepared by the modified Pechini method. The series of samples with various Eu3+ concentrations in the range of 0.1% up to 4% and the different average grain size from 31 to 75nm were obtained. YAG:Eu3+ nanoceramics were fabricated by the low temperature high pressure sintering technique (LTHP). Comprehensive studied with microsized grains ceramic as a reference were performed. The photoluminescence and cathodoluminescence properties of YAG:Eu3+ nanoceramic were performed at room temperature. In particular, the influence of dopant concentration and grain size of nanocrystals on the cathodoluminescence and photoluminescence properties was analyzed. The changes of the luminescent asymmetric ratio associated with the change in local symmetry for nanocrystals, nanoceramics and microceramics was investigated.