Cross Relaxation in rare-earth-doped oxyfluoride glasses

The excited-state relaxation dynamics of Tb3+, Sm3+, and Eu3+ doped into a 50SiO2–20Al2O3–10Na2O–20LaF3 (mol%) oxyfluoride glass are studied. Multiphonon relaxation of the primary emitting states in Tb3+ (5D3 and 5D4), Sm3+ (4G5/2), and Eu3+ (5D0) was found to be negligible in the present host. The relaxation of Tb3+ (5D4) and Eu3+ (5D0) is dominated by radiative decay. For Tb3+ (5D3) and Sm3+ (4G5/2) in contrast, radiative relaxation is in competition with several non-radiative cross-relaxation processes. This competition was found to be particularly pronounced for the 5D3 excited state in Tb3+, where a 124-fold decrease of the (5D3→7F5)/(5D4→7F5) emission intensity ratio and a ∼10-fold shortening of the 5D3 lifetime was observed upon increasing the Tb3+ concentration from 0.01% to 1%. The Tb3+ concentration dependence of 5D3 also points to some degree of ion aggregation in the "as quenched" glasses. A Judd–Ofelt intensity analysis was performed for Sm3+ and used to estimate the relative magnitude of 4G5/2 cross-relaxation processes. Four cross-relaxation processes in particular were identified to account for 92% of the total 4G5/2 non-radiative decay, and a 11% quantum efficiency was estimated for the 4G5/2 excited state. Non-exponentiality in the 5D0 decay of Eu3+ is evidence for several Eu3+ coordination environments in the glass host that manifest in different 5D0 decay constants because of the hypersensitivity of the 5D0→7F2 transition. -- Highlights: ► Tb3+, Sm3+, and Eu3+ were doped into a LaF3-rich oxyfluoride glass. ► The 5D3 cross relaxation rate of Tb3+ can be tuned via concentration. ► The 5D3/5D4 emission intensity ratio was used as a probe for Tb3+ ion aggregation. ► Cross relaxation dominates the decay of the 4G5/2 excited state of Sm3+. ► Multiple Eu3+ sites yield a non-exponential 5D0 decay via 5D0→7F2 hypersensitivity