Luminescent Properties of Divalent Samarium-Doped Strontium Hexaborate

The valence change of samarium from trivalent to divalent in strontium hexaborate (SrB 6 O 10 ) prepared in air is observed. The temperature dependence of the luminescence and vibronic transitions of Sm 2+ are studied. The Sm 2+ ions occupy three crystallographic sites. With increasing temperature, the 5 D 0 → 7 F 0 transition line exhibits red shifts, and the half-width increases. At room temperature, due to the thermal population through the 4f 5 5d channel, the 5 D 1 → 7 F J transitions are observed even though the vibrational energy is very close to the energy gap between the 5 D 1 and 5 D 0 levels in the host. A coupled phonon energy of about 108 cm - 1 is determined from the vibronic transitions of Sm 2+ in the host.