The contribution of the coordinated water to 5D4 population in YPO4 hydrates doped with low concentration of Tb3+

This work reports an interesting result on the photoluminescence of YPO4 · 2H2O doped with low concentration of Tb3+, which was synthesized at low temperature by aqueous route. In the as-synthesized Y0.098PO4:Tb0.002 · 2H2O, in which the hydration water is coordinated to the rare earth ions, the emissions of 5D4 of Tb3+ are much more intense than the emissions of 5D3. After dehydration by annealing, an opposite result is achieved, i.e., the emissions of 5D4 of Tb3+ are much lower than the emissions of 5D3. The Fourier-transform infrared (FTIR) and fluorescent decay spectra demonstrate that the coordinated water molecule in the hydrated sample contributes to the relaxation of 5D3 to 5D4, thus increasing the population of the excited state 5D4 of Tb3+ in the as-synthesized sample.