On the synthesis of LuAG:Ce fine powders by molten salts methods and spectroscopic properties of the products

Lu3Al5O12:Ce (LuAG:Ce) powders were synthesized at temperatures as low as 450-550 °C by means of a molten salts technique with eutectic mixtures of NaNO2 and KNO2 or NaNO2, KNO2 and Na2CO3. Addition of sodium carbonate allowed getting phase pure cubic LuAG:Ce even at 450 °C while without it the needed temperature was 500 °C. The powders had well defined morphology with particles sizes reaching 200-250 nm or 150-250 nm when Na2CO3 was used. The spectroscopic properties of the materials were characterized in the 17-700 K range of temperatures. The ratio of the two Ce3+ related excitation bands located at 345 and 450 nm were found to increase significantly between 17 K and 350 K while above that range of temperatures it was quite constant. This ratio was shown to vary strongly depending on the atmosphere of synthesis. Heating at 1150 °C in air reduced the efficiency of the excitation into the 345 nm very significantly, which was ascribed to formation of defects, among them also appearance of Ce4+, whose competing absorption overlapping the 345 nm excitation band effectively reduced its contribution to the luminescence compared to the 450 nm band. Decay times were pretty constant in the 17-300 K range of temperatures and also were independent on the atmosphere of post-fabrication heat-treatment.