Pressure-induced Pr3+ 3P0 luminescence in cubic Y2O3

An explanation for the puzzling absence of luminescence from the Pr3+ 3PJ[=0,1,2] states in C-Ln2O3 (cubic; Ln3+=Lu3+, Y3+, Gd3+) family of materials is provided by conducting a study of the emission properties of C-Y2O3:Pr3+ under applied hydrostatic pressure. Above 7 GPa, electronic transitions from the Pr3+ 3PJ[=0,1,2] states are observed in the emission spectrum of C-Y2O3:Pr3+ at room temperature and below. The experimental data reveal that the crystal-field split Pr3+ 4f15d1 configuration is located entirely within the host lattice conduction band and that the promotion of the electron to the Pr3+ 4f15d1 state produces a self-trapped exciton-like state with the configuration, [Pr4++eCB], where eCB indicates an electron in the host lattice conduction band. Upon excitation, the exciton-like state bypasses the upper emitting 3PJ[=0,1,2] states and directly feeds the lower emitting 1D2 state. This explains the absence of optical transitions from the Pr3+ 3PJ[=0,1,2] states in the emission spectrum of C-Y2O3:Pr3+ at ambient pressure. At high pressures, emission transitions from the Pr3+ 3PJ[=0,1,2] states are observed because of the localization of the Pr3+ 4f15d1 state to below the host lattice conduction band edge.