Lengthening of the Sm²⁺ 4f⁵5d → 4f⁶ decay time through interplay with the 4f⁶[⁵D₀] level and its analogy to Eu²⁺ and Pr³⁺

Recent research activity on Sm²⁺-doped compounds has significantly increased the amount of available data on 4f⁵5d → 4f⁶ decay times. This enabled the systematic comparison of spectroscopic and time resolved luminescence data to theoretical models describing the interplay between the 4f⁵5d and 4f⁶[⁵D₀] excited states on the observed decay time. A Boltzmann distribution between the population of the excited states is assumed, introducing a dependence of the observed 4f⁵5d → 4f⁶ decay time on the energy gap between the 4f⁵5d and 4f⁶[⁵D₀] levels and temperature. The model is used to interpret the origin of the large variation in reported 4f⁵5d → 4f⁶ decay times through literature, and links their temperature dependence to applications such as luminescence thermometry and near-infrared scintillation. The model is further applied to the analogous situation of close lying 4f^n-15d and 4fⁿ states in Eu²⁺ (⁶P_7/2) and Pr³⁺ (¹S₀).