Frequency upconversion involving quartets of ions in a Pr3+/Eu3+ oxyfluoroborate glass

Upconversion emission from 3P0 level of Pr3+ has been observed on excitation with 496.5 nm line of Ar+ laser when Pr3+ and Eu3+ are codoped in oxyfluoroborate glass. No fluorescence is observed when only Pr3+ is present in the glass but even a small amount of Eu3+ leads to this fluorescence (3P0 → 3H4, 3P0 → 3F2) along with fluorescence from 5D0 level of Eu3+. The observed fluorescence of Pr3+ has been explained as being due to energy transfer from a pair of Eu3+ ions to a pair of Pr3+ ions.