Luminescence of Cr3+ and energy transfer between Cr3+ and Nd3+ ions in yttrium aluminum garnet

The luminescence properties of Cr3+ ions and the energy transfer between Cr3+ and Nd3+ ions have been studied quantitatively in yttrium aluminum garnet (YAG). The energy level diagram and the emission spectrum of 4T2→4A2 transition of Cr3+ ions were calculated in this crystal using the single-configurational-coordination model and the absorption data. Our calculated Δ value (the energy difference between the 2E zero-vibrational level and the crossover point of 2E and 4T2 states), ∼730 cm−1 at room temperature, in contrast to the previously estimated value of ∼1000 cm−1, accounts for a variety of experimental results more satisfactorily. Both the 4T2 and 2E states of Cr3+ ions were found to contribute to the energy transfer to Nd3+ ions. The contribution of the former dominates at high temperatures and the latter at low temperatures. The thermal population distribution between the 4T2 and 2E states of Cr3+ ions was shown to be responsible for the temperature dependences of the Cr3+ luminescence properties and the Cr3+ to Nd3+ energy transfer processes. An electric dipole–dipole interaction mechanism was found to be adequate to describe the energy transfer process for temperatures up to about 400 K.