Unusually fast energy transfer in solid state crystals and glasses

The laser performance of rare earth doped crystals and glasses can be significantly improve by codoping with an additional ion which absorbs the pump light and efficiently transfers the energy to the lasing rare earth ion. Such methods have been used in chromium-neodymium doped gadolinium scandium gallium garnets, glasses and glass ceramics, and manganese-thulium doped lead zinc gallium fluoride glasses. Energy transfer between donors and acceptors in such materials has been traditionally modeled by the Foerster-Dexter equation. However, it has been found recently that an anomalous energy transfer can occur at very short times inconsistent with the above model. We propose that such transfer can occur due to two additional causes: 1. the physical pairing of donors and acceptors in the materials and 2. additional short-range interactions which noticeably increase the transfer rate between donors and acceptors. Models for both these cases are presented and compared with experimental results.