Al2O3–Ce:YAG composite ceramics for high brightness lighting: Cerium doping effect

Efficient Al2O3–Ce:YAG composite ceramic phosphors were obtained via reactive vacuum sintering using commercial α-Al2O3, Y2O3, and CeO2 powders as starting materials, and SiO2, MgO as a complex sintering additive. The effect of cerium content (0.05–0.3 at%) on the structural-phase state, optical and photoluminescent properties of ceramic phosphors were investigated comprehensively by X-ray diffraction, high-resolution scanning electron microscopy, energy-dispersive X-ray spectroscopy, electron backscatter diffraction, confocal laser scanning microscopy, ultraviolet-visible spectrophotometry, and photoluminescence examinations. It is shown that an increase in the cerium doping level of the composites initiates their partial recharging into the non-luminescent Ce4+ state and the parasitic introduction of magnesium ions into the aluminum oxide phase due to the stabilization of the crystal structure of Mg,Si,Ce:YAG solid solutions. The highest value of the photoluminescence intensity is observed for the 0.1 at% Ce3+ sample, which may be caused by the optimal ratio of its absorbance and radiative recombination rate compared to other samples. The obtained ceramic phosphors show excellent thermal quenching behavior – reduction in the photoluminescence emission intensities did not exceed 5% at heating temperatures to 150 °C, which can be regarded as almost unchanged. The correlated color temperature values of 1.0 and 0.4-mm-thick Al2O3–Ce:YAG samples with 0.05–0.3 at% Ce3+ doping varied between 4583 and 3890 K and 10,308–4146 K at color rendering index values of 61–35 and 74–55, respectively. It is concluded that 0.05–0.1 at% Ce3+-doped ceramic phosphors have an optimal balance between a high color rendering index, luminous efficiency, and appropriate correlated color temperature values for high-power and high-brightness natural white light-emitting diodes.