Effect of bismuth oxide on the thermal stability and Judd–Ofelt parameters of Er3+/Yb3+ co-doped aluminophosphate glasses

The Er3+/Yb3+ co-doped glasses with compositions of xBi2O3–(65 − x)P2O5–4Yb2O3–11Al2O3–5BaO–15Na2O (where x = 0, 2.5, 5, 7.5 and 10 mol%) were prepared using the normal melt quench technique. The optical absorption spectra of the glasses were recorded in the wavelength range 300–1700 nm. The effect of Bi2O3 content on the thermal stability and absorption spectra of glasses was investigated. In addition, the Judd–Ofelt parameters and oscillator strengths were calculated by employing Judd–Ofelt theory. It was observed that the positions of the fundamental absorption edge and cut-off wavelength shifted towards red as the content of Bi2O3 increased. However, there were no red shifts found both in the peak wavelength and in the center of mass wavelength of all absorption bands with Bi2O3 content increasing. The results of Judd–Ofelt theory analysis showed that Judd–Ofelt parameters Ωt (t = 2, 4, 6) changed sharply when Bi2O3 concentration exceeded 5 mol%. The variation trends of experimental oscillator strength were similar with those of Judd–Ofelt parameters as function of Bi2O3 concentrations. Moreover, differential scanning calorimetry experiments showed that the increases of Bi2O3 content weakened the network structure and then lowered the thermal stability of the glasses. The spontaneous emission probability Arad, branching ratio β and the radiative lifetime τrad were also calculated and analyzed. The stimulated emission cross-section of Er3+ was calculated according to the McCumber theory. It was found that the stimulated emission cross-section of Er3+ was monotonically increases with Bi2O3 content increasing.