Combustion Synthesis and Photoluminescence Properties of YNbO₄-Based Nanophosphors

YNbO 4 and YNbO 4:RE (RE = Er 3+, Sm 3+, Tb 3+, and Tm 3+ ) nanophosphors have been prepared using a citrate-gel combustion procedure. The results of X-ray diffraction reveal that the YNbO 4 samples crystallized in both monoclinic and tetragonal phases in the investigated temperature range. The excitation spectra of the undoped YNbO 4 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 YNbO 4 . Upon UV excitation of the niobate host, characteristic emissions from f−f transitions of the RE ions were observed. The luminescence covers the blue (Tm 3+ ), green (Er 3+, Tb 3+ ), and orange−red (Sm 3+ ). The mechanism of the energy transfer between the niobate host and the RE ions was deduced.