Synthesis and characterization of ZnO nanocrystals co-doped with Ce$^{3+}$ and Tb$^{3+}$

Rare earth doped zinc oxide nanocrystals produce visible emissions under ultraviolet excitation. Using a sol-gel process, we synthesized a series of ZnO nanocrystals doped with Tb$^{3+}$ and Ce$^{3+}$ in silica glass, keeping the ZnO/SiO$_2$ ratio constant at 10/90 and doping with 1\% rare earth by weight, with varying relative concentrations of Tb$^{3+}$ and Ce$^{3+}$. The nanocrystals were characterized using photoexitation and emission spectroscopy, time-resolved photoluminescence, UV/VIS spectroscopy, and transmission electron microscopy. We determined that co-doping with cerium enhanced the visible terbium emissions to a point, with the most effective enhancement occurring at mid-range Ce$^{3+}$ concentrations.