Luminescence and microstructure of $Sm2+$ ions reduced by x-ray irradiation in $Li2O–SrO–B2O3$ glass

$Sm3+$-doped $Li2O–SrO–B2O3$ glass sample was prepared by the conventional melt quenching method in air atmosphere. $Sm2+$ ions in this borate glass were obtained by x-ray irradiation reduction method. The as-prepared and x-ray-irradiated samples were investigated by photoluminescence spectrum and decay curve measurements. The dependence of $Sm2+$ luminescence intensity on the x-ray irradiation time was investigated. It is found that the conversion of $Sm3+→Sm2+$ after x-ray irradiation is efficient in this borate glass. Photostability of $Sm2+$ ions was evaluated by the photobleaching method. Furthermore, the induced optical absorption spectrum measurement after x-ray irradiation was performed. Thermoluminescence above room temperature was also studied after x-ray irradiation. The different kinds of defect structures and the reduction mechanism of $Sm2+$ ions in this borate glass were discussed. The microstructure of Sm ions in the $Li2O–SrO–B2O3$ glass was suggested. The proposed microstructure would be helpful to understand the reduction mechanism of $Sm2+$ ion in borate glasses.