Benyuan Ma

Transparent Ce:Y3Al5O12 ceramic phosphors for white light-emitting diodes

We present our recent achievement of a transparent ceramic able to produce white light when directly combined with commercially available blue light emitting diodes. The photoluminescence properties of ceramic phosphor (Y1-xCex)(3)Al5O12 are studied as a function of doping fraction (x = 0.0005-0.0020). The emission color is tunable by variations of Ce3+ concentration and ceramic phosphor thickness. A maximum luminous efficacy exceeding 93 lm/W at a low correlated color temperature of similar to 4600 K is obtained, which is superior to samples made from commercial phosphor powders. Hence, the present transparent ceramic phosphor is expected to be an ideal candidate for generating white light

A study on the effect factors of sol-gel synthesis of yttrium aluminum garnet nanopowders

Yttrium aluminum garnet (YAG) nanopowders were synthesized by sol-gel method using aluminum nitrate, yttrium nitrate, and citric acid as starting materials, de-ionized water, ethanol, and ethylene glycol as solvents, respectively. The phase formation process, state of particle size distribution (PSD), compositions, morphological characteristics, and thermal behavior of the powders were investigated by means of x-ray diffractometry, PSD, Fourier transform infrared, transmission electronic microscope, and thermogravimetry-differential scanning calorimetry. Results indicate that the formation and characteristics of precursor gel and YAG powder, such as the rate of gelation, average particle size, and powder agglomerate state, strongly depend on the stoichiometric amount of citric acid, the solvent composition, and the precalcination process. Highly crystalline, well-dispersed YAG nanopowder was obtained by calcining at 800 degrees C for 2 h in the presence of citric acid to nitrate ratio of 3, ethanol solvent, and precalcination process. According to the analysis of experimental results, sol-gel chemistry, DLVO theory, and steric effect, the effects of stoichiometric amount of citric acid, solvent composition, and precalcination process on the formation and characteristics of precursor gel and YAG powder have been discussed. Meanwhile, the overall synthesis mechanism in sol-gel method has been suggested.

Novel phenomenon on valence unvariation of doping ion in Yb:YAG transparent ceramics using MgO additives

Yb:YAG nanopowders were synthesized by the alcohol-water co-precipitation method adding MgO as sintering additives. Appropriate amount of MgO adding can restrict the agglomeration and reduce the particle size of Yb:YAG powders. When the MgO content was 0.04wt%, well-dispersed Yb:YAG powders with ellipsoidal particles of less than 100 nm diameter were obtained. The experimental results showed the valence variation of doping ion Yb3+ would not appear when adding MgO as sintering additives, so ceramics showed colorless transparent instead of green due to Yb2+ color center using traditional SiO2 as additives. The transmission of the sintered Yb:YAG ceramics can reach 80.6% even without annealing. Ceramic morphology showed that the grains had uniform-distribution with the size of 10 μm or so, and no impurity and pore existed in the grain boundary and crystalline while using optimal sintering conditions.