Energy transfer and radiationless relaxation processes in Nd and Cr doped mixed garnet crystals

Four-wave mixing and flourescence dynamics measurements have been used to investigate the energy transfer processes in (Gd,Ca)₃(Ga,Mg,Zr)₂Ga₃O₁₂ crystals doped with Nd³⁺ or codoped with Cr³⁺ and Nd³⁺ ions. The results show that strong, short range energy transfer takes place between Cr³⁺ and Nd³⁺ ions and this is enhanced by long range energy migration among the Cr³⁺ ions. Energy migration was also found to occur among the Nd³⁺ ions. The energy migration properties are affected by the active ion concentration, the distribution of active ions, ion-ion iteraction rates, and temperature. In addition, the pump band to metastable state radiationless relaxation process in the Cr³⁺ ions was characterized by determining the values of the dephasing time from the properties of the four-wave mixing signal. The effects of anharmonic coupling are needed to explain the variation of the T₂-dephasing time as a function of the crystal field splitting between the ²E and ⁴T₂ levels for a series of Cr³⁺-doped materials.