Anomalous luminescence dynamics of Eu~(3+) in BaFCl microcrystals

摘要

Spectroscopic properties of Eu~(3+) ions (< 0.1 at %) at two main sites of BaFCl microcrystals are investigated. For Eu~(3+) ions at site Ⅰ the energy levels and luminescence intensity distribution are similar to most other normal systems ever reported. But the ~5D_0 lifetime of Eu~(3+) at site Ⅰ decreases rapidly with the temperature and the nonradiative energy transfer (ET) rate is observed to be T~2 dependence. In contrast, Eu~(3+) at site Ⅱ shows unusual energy level structure and luminescence intensity distribution with the strongest ~5D_0 → ~7F_0 transition. The nonradiative ET rate of Eu~(3+) at site Ⅱ obeys a T~9 dependence. Spectroscopic results and theoretical analyses indicate that site Ⅱ is associated with the charge compensator O~(2-) occupying the nearest F~- site around Eu~(3+). The mechanisms for anomalous luminescence properties at both sites are further discussed based on the model of charge transfer vibronic exciton (CTVE) and charge-imbalance induced large linear crystal-field potential.