Y3Al5O12 Transparent Ceramics Research Articles

Ce/Mn/Cr: Y3Al5O12 phosphor ceramics for white LED and LD lighting with a high color rendering index

Ce/Mn/Cr: Y3Al5O12 transparent ceramics with a pure garnet structure and a high color rendering index were prepared by a solid-state reaction method. Mn2+ and Cr3+ enhance the emission between 500 and 700 nm and expand the conventional Ce: YAG phosphors spectrum. The Ce3+ can work both, as activators and sensitizers, and the intense energy transfer from Ce3+ to Mn2+/Cr3+ is realized through the non-radiative and radiative processes. In the sample with the optimized doping concentration the high color rendering index (CRI) value of 75.3 can be achieved under a 450 nm laser diode excitation. The chromaticity coordinates can be tuned from (0.3125, 0.3232) to (0.2917,0.2851) by varying the doping concentration. With the increasing Mn2+/Cr3+ doping concentration, the lifetime of Ce3+, quantum efficiency and luminous efficiency are all gradually decreased. This work effectively offers a scheme for realizing the high color rendering performance of phosphor-converted transparent ceramics in white LEDs/LDs.

Comparative study of Ho:Y2O3 and Ho:Y3Al5O12 transparent ceramics produced from laser-ablated nanoparticles

Ho:Y2O3 and Ho:Y3Al5O12 transparent ceramics are fabricated by vacuum sintering at 1780 °C for 20 h from laser-ablated nanopowders (Ho:Y2O3 and Ho:Y2O3 + Al2O3) using ZrO2 and TEOS as sintering aids, respectively. The sesquioxide ceramic exhibits smaller grain size (∼5.4 μm), smaller content of pores (down to 6 ppm) and higher optical transmission (up to 82.2% at ∼1 μm) than the garnet one. A detailed comparative spectroscopic study of the two ceramics is performed. For the 5I7 → 5I8 Ho3+ transition, the maximum stimulated-emission cross-sections and the luminescence lifetimes are σSE = 0.57 × 10−20 cm2 at 2087.1 nm and τlum = 10.92 ms (for the Ho:Y2O3 ceramic) and σSE = 1.70 × 10−20 cm2 at 2090.8 nm and τlum = 7.04 ms (for the Ho:Y3Al5O12 one) The rates of multiphonon relaxation are determined for both ceramics. For the Ho:Y2O3 ceramic, they do not exceed those for single-crystals. The crystal-field splitting of Ho3+ multiplets (5I7 and 5I8) is determined at 12 K and analyzed using the barycenter plot. Due to its broadband emission properties, the Ho:Y2O3 ceramic is suitable for mode-locked lasers emitting above 2 μm.

Efficient spectral regulation in Ce:Lu3(Al,Cr)5O12 and Ce:Lu3(Al,Cr)5O12/Ce:Y3Al5O12 transparent ceramics with high color rendering index for high-power white LEDs/LDs

Realizing a high color rendering index (CRI) in Ce:LuAG transparent ceramics (TCs) with desired thermal stability is essential to their applications in white LEDs/LDs as color converters. In this study, based on the scheme of configuring the red component by Cr3+ doping, an efficient spectral regulation was realized in Ce,Cr:LuAG TCs. A unilateral shift phenomenon could be observed in both photoluminescence (PL) and photoluminescence excitation (PLE) spectra of TCs. By constructing TC-based white LED/LD devices in a remote excitation mode, luminescence properties of Ce,Cr:LuAG TCs were systematically investigated. The CRI values of Ce:LuAG TC based white LEDs could be increased by a magnitude of 46.2%. Particularly, by combining the as fabricated Ce,Cr:LuAG TCs with a 0.5 at% Ce:YAG TC, surprising CRI values of 88 and 85.5 were obtained in TC based white LEDs and LDs, respectively. Therefore, Ce,Cr:LuAG TC is a highly promising color convertor for high-power white LEDs/LDs applied in general lighting and displaying.

Dual effect synergistically triggered Ce:(Y,Tb)3(Al,Mn)5O12 transparent ceramics enabling a high color-rendering index and excellent thermal stability for white LEDs

Ce:Y3Al5O12 transparent ceramics (TCs) with appropriate emission light proportion and high thermal stability are significant to construct white light emitting diode devices with excellent chromaticity parameters. In this work, strategies of controlling crystal-field splitting around Ce3+ ion and doping orange-red emitting ion, were adopted to fabricate Ce:(Y,Tb)3(Al,Mn)5O12 TCs via vacuum sintering technique. Notably, 85.4 % of the room-temperature luminescence intensity of the TC was retained at 150 °C, and the color rendering index was as high as 79.8. Furthermore, a 12 nm red shift and a 16.2 % increase of full width at half maximum were achieved owing to the synergistic effects of Tb3+ and Mn2+ ions. By combining TCs with a 460 nm blue chip, a warm white light with a low correlated color temperature of 4155 K was acquired. Meanwhile, the action mechanism of Tb3+ ion and the energy transfer between Ce3+ and Mn2+ ions were verified in prepared TCs.

A new approach to Y3Al5O12 transparent ceramics by vacuum sintering of spray-dried xerogels

We report fabrication of Y3Al5O12 optical ceramics via compaction of amorphous xerogel obtained by spray-drying of 5AlOOH(NO3)0.07·3Y(OH)2(CH3COO) aggregation-resistant sol, calcination to convert it into garnet phase and subsequent vacuum sintering. The spray drying conditions of the hydrosol have been optimized to ensure formation of spherical granules of xerogel with average diameter of about 330nm. The thermal decomposition of amorphous precursor and its conversion to pure garnet phase have been studied by DSC, TG and XRD methods. Pressing of the xerogel allows one to achieve quite uniform microstructure of green bodies with well-developed net channels of pores which is beneficial for achieving high sinterability. Transparent Y3Al5O12 ceramics possessing the in-line transmission of about 80% at λ=1064nm and the residual porosity of ∼5×10−3vol% have been obtained by vacuum sintering of the amorphous xerogels with the green density of 26%.

Effect of air annealing on the color center in Yb:Y3Al5O12 transparent ceramics with MgO as sintering additive

High quality Yb:Y3Al5O12 (YAG) transparent ceramics were fabricated by vacuum sintering with MgO as sintering aids. The Yb:YAG samples were annealed at 1250–1450°C for 20h in air. The experimental results showed that the transparency of Yb:YAG samples declined markedly with the annealing temperatures of 1250–1450°C. The samples became increasingly orange-yellow in color with the increase of annealing temperature. The potential reasons of discoloration were discussed for the first time. It was attributed to the complex color center [Mg2+F+] formed during the annealing, which was evidenced by optical absorption in the range of 300–500nm wavelength and the presence of an electron spin resonance (ESR) line at g=1.9806. The formation mechanism of the complex color center was explained in detail. The complex color center can be eliminated after post-HIP (hot isostatic pressing). And by air annealing and post-HIP, the transmittance of the samples increased from 80.3% to 83.4%.

Optical properties and laser oscillation of Yb3+, Er3+ co-doped Y3Al5O12 transparent ceramics

We reported a kind of Yb3+ and Er3+ co-doped Y3Al5O12 (Yb, Er:YAG) transparent ceramics fabricated by using one-step vacuum sintering. The decent optical properties of the samples, e.g., high in-line transmittance up to 83.4% (at 1.6μm), are benefit from their fine structures, in which the average grain size is 15μm, without any pores spotted within the scope. The absorption around 970nm of this co-doped ceramic reaches nearly 4.8 times that of the single Er3+ doped YAG. Laser operation at 1645nm was evaluated by using a commercial laser diode emitting at 970nm. The maximum output power of 155mW was acquired with an optical-to-optical efficiency of 2.8%.

Sensitized Yb3+ emission in (Nd, Yb):Y3Al5O12 transparent ceramics

The characteristics of Nd→Yb energy transfer in (Nd, Yb):Y3Al5O12 (YAG) transparent ceramics, obtained from steady state and dynamic spectral studies on different single doped and codoped samples, prepared by solid state synthesis, are presented. The Yb3+ emission in codoped (Nd, Yb):YAG samples under cw excitation of the donors (Nd3+) revealed efficient energy transfer to Yb3+ (at low temperatures too), due to the overlap of the Nd3+ F43/2→I49/2 emission and Yb3+ F27/2→F25/2 absorption. From the global decays of the Nd3+ F43/2 level in single and codoped samples, the transfer efficiencies were estimated; they increase with Yb3+ content reaching ∼93% for 1 at. % Nd, 5 at. % Yb:YAG sample. The mechanisms and parameters of the Nd→Yb energy transfer were inferred from the Nd3+ decays in the codoped samples, after the separation of the self-quenching inside the donors (Nd3+) from the transfer to acceptors (Yb3+). It was proved that the Nd→Yb energy is resonant and dominated by dipole-dipole interactions. Due to the large transfer efficiencies, (Nd, Yb):YAG ceramic could be a promising material for Yb3+ emission under pumping in strong Nd3+ absorption lines.