Combustion Synthesis and Photoluminescence Properties of YNbO4-Based Nanophosphors

YNbO4 and YNbO4:RE (RE = Er3+, Sm3+, Tb3+, and Tm3+) nanophosphors have been prepared using a citrate-gel combustion procedure. The results of X-ray diffraction reveal that the YNbO4 samples crystallized in both monoclinic and tetragonal phases in the investigated temperature range. The excitation spectra of the undoped YNbO4 samples exhibit a red-shift as annealing temperature or time increases, and the emission spectra show a broadband around 400 nm, corresponding to the self-activated luminescence center of YNbO4. Upon UV excitation of the niobate host, characteristic emissions from f-f transitions of the RE ions were observed. The luminescence covers the blue (Tm3+), green (Er3+, Tb3+), and orange-red (Sm3+). The mechanism of the energy transfer between the niobate host and the RE ions was deduced.