Electronic polarizability and optical parameters of Er3+/Yb3+co-doped phosphate glasses

Abstract

The samples of Er 3+ /Yb 3+ co-doped phosphate glasses with different Er 3+ doped concentrations were prepared by high-temperature melting method. By calculating the electronic polarizabilities and optical basicity of the samples, we find, with the increasing of Er 3+ ions concentration, the polarizability and optical basicity of oxide ions become large, which indicates that the covalence of the glasses becomes small. Based on Judd-Ofelt (J-O) theory, the J-O intensity parameters Ω λ (λ=2,4,6), spontaneous radiative lifetime, and fluorescence branching ratio were calculated. With the increasing of Er 3+ concentration, the Ω 2 values are decrease gradually, which also proves that the covalence of the glasses becomes small. The ratios of Ω 4 /Ω 6 are within the range of 7.51-9.84, which are larger. Thereby, our glasses are suitable laser materials. We also studied the upconversion (UC) emission of the samples. The strong 657 nm red emission, 546 nm and 523 nm green emissions were observed under 975 nm laser diode (LD) excitation. The UC emission intensities depend on the ratio of Er 3+ /Yb 3+ . When the ratio is 0.125, the emissions are strongest. The emission cross sections of UC emissions were analyzed using McCumber theory and Fuchtbauer Ladenburg (FL) method. The emission cross section of UC red emission is larger (about 0.5×10 -20 cm 2 ),which proves our samples are better red light materials.