Energy Spectra of the Tunable Laser Crystal Gd3Ga5O12:Cr3+ and Their Pressure-Induced Shifts

By means of both the theory for pressure-induced shifts(PS) of energy spectra and the theory for shifts of energy spectradue to electron-phonon interaction (EPI), at 300 K,the `pure electronic' contributions andthe contributions from EPI to R₁ line, R₂ line, and U band ofGGG:Cr³⁺ as well as their PS have been calculated, respectively.The total calculated results are in good agreement with all theexperimental data. Their physical origins have been explained.It is found that the mixing-degree of |t₂²(³T₁)e⁴T₂> and |t₂³²E> base-wavefunctions in the wavefunctions of R₁ level of GGG:Cr³⁺ is considerableunder normal pressure, and the mixing-degree rapidly decreaseswith increasing pressure. The change of the mixing-degree withpressure plays a key role for PS of R₁ line or R₂ line. At300 K, both the temperature-independent contribution to R₁ line(or R₂ line or U band) from EPI and the temperature-dependent oneare important. The remarkable difference between pressure-dependentbehaviors of PS of R₁ lines of GGG:Cr³⁺ and GSGG:Cr³⁺ resultsfrom the differences of their microscopic properties. The featuresof emission spectra of GGG:Cr³⁺ at various pressures have satisfactorilybeen explained.