Effects of citric acid additive on photoluminescence properties of YAG:Ce3+ nanoparticles synthesized by glycothermal reaction

We synthesize Y3Al5O12:Ce3+ (YAG:Ce3+) nanoparticles in the presence of citric acid by glycothermal method. Fourier transform infrared absorption spectroscopy measurement indicates that the intensity of the peak corresponding to carboxyl groups coordinating to the nanoparticles increases with increasing amount of citric acid. At the same time, the primary particle diameter decreases from 10.2 to 4.0 nm. In addition, the internal quantum efficiency of the photoluminescence (PL) due to the 4f-5d transition of Ce3+ increases from 22.0% to 40.1% with increasing amount of citric acid. Two kinds of PL decay lifetimes, 16-26 and 72-112 ns, are detected for YAG:Ce3+ nanoparticles, whereas the micron sized YAG:Ce3+ bulk shows the lifetime of 57 ns. We discuss these phenomena from the aspects of the coordination of citric acid and the incorporation of Ce3+ ions into the nanoparticles.