The reduction of RE3+to RE2+(RE=EU, Sm and Tm) in SrB6O10prepared in air by high-temperature solid state reaction was observed. The luminescent properties of Eu2+and Tm2+show f-d transition and Sm2+shows f-f transition at room temperature. Three crystallographic sites for Sm2+in matrix are available. Vibronic transition of5D0-7F0of Sm2+was studied. The coupled phonon energy about 108 cm−1, was determined from the vibronic transition. Due to the thermal population from5D0level,5D1-7Fj(J=0, 1, 2) transitions of Sm2+were observed at room temperature. A charge compensation mechanism is proposed as a possible explanation.