The luminescence of Sm2+ in alkaline earth borophosphates

The temperature-dependent luminescence of Sm²⁺ ions in MBPO₅ (M = Ca²⁺, Sr ²⁺, Ba²⁺ was studied. At low temperature, Sm²⁺ in this series shows 4f⁶-4f⁶ luminescence with only a single emission line observed for the ⁵D₀→⁷F₀ transition, revealing that only one crystallographic cationic site is available for Sm²⁺ in all the hosts. With increasing temperature, the emission intensity of the ⁵D₀→⁷F₀ transition increases whereas that of the ⁵D₀→⁷F₁ transitions decreases. The ⁵D₁→⁷F₀ transitions of Sm²⁺ were observed in BaBPO₅ and its intensity increases with increasing temperature. At 450 K, a broad band of the 4f⁵5d-4f⁶ luminescent transition of Sm²⁺ in SrBPO₅ and BaBPO₅ with maximum at ~600 nm appears due to the thermal population. The lifetime of the ⁵D₀→⁷F₀ transition was recorded at different temperatures, showing a single exponential decay for Sm²⁺ in SrBPO₅ and BaBPO₅ but a nonsingle- exponential decay in CaBPO₅.