Photoluminescence studies of Sm2+ in the stimulable phosphor SrS:Eu,Sm

The doubly rare-earth doped phosphor SrS:Eu,Sm is representative of a class of stimulable phosphors that may find application in optical data storage and related areas of photonic technology. The infrared photoluminescence (PL) from the Sm2+ ions is a potentially useful probe of the "written" state of this phosphor, i.e., the right-hand side of the charge-transfer reaction (Eu2++Sm(3+)reversible arrow Eu3++Sm2+). In the present study, several properties of the Sm2+ PL from bulk ceramic SrS:Eu,Sm were examined, including the emission spectrum, temperature dependence from 14 to 300 K, electron-phonon coupling, excitation spectrum, and excitation intensity dependence. The full width at half maximum of the PL emission spectrum, W(T), was found to increase with temperature in a manner consistent with a linear electron-phonon coupling model, W(T) = W-o[tanh(Omega/(2k(B)T))](-1/2), with W-o=0.190 eV and coupled phonon energy Omega=0.026 eV. Periodic oscillations in the PL spectrum at T<60 K provide direct evidence for coupling to two phonon modes, with phonon energies Omega(1) = 0.0155 eV and Omega(2) = 0.028 eV. The peak of the emission spectrum occurs at 0.709 eV at 14 K and increases with temperature at a rate 1.9x10(-4) eV/K. The electron-phonon coupling model predicts that the corresponding optical absorption peak, which is anti-Stokes shifted relative to the PL peak, should occur at 1.17 eV at low temperature, or 1.23 eV at room temperature. Previous measurements of the charge-transfer excitation spectrum in SrS:Eu,Sm showed a peak at 1.25 eV, in good agreement with the model prediction. The PL excitation spectrum from 1.7 to 6.2 eV was measured at T=14 K. Excitation peaks were observed at 2.08 eV, ascribed to absorption to a higher excited Sm2+ state; at 2.65 eV, ascribed to Eu2+ absorption followed by Eu-->Sm charge transfer; at 2.92 eV; and at 4.49 eV, ascribed to interband excitation of the SrS. [S0163-1829(98)03819-3].