Optical properties of chromium (III) in MIIn(WO4)2 hosts, where MI = Li, Na, K, Rb

Optical absorption, excitation and emission spectra have been measured for double indium tungstate crystals with the formula (MCrxIn1-x)-Cr-I(WO4)(2) (x = 0.5-2%, M-I = Li, Na, K and Rb) at temperatures ranging from 5 to 300 K. The broadband T-4(2)-(4)A(2) luminescence from low-crystal-field Cr3+ sites was observed in all the crystals that were studied. The local structure of the Cr3+ surroundings is discussed in terms of the spectroscopic results, and the crystal field parameters, Dq, B and C of the Cr3+ ion are derived for all the materials. The Huang-Rhys parameters, S, and breathing phonons, (h) over bar omega, are reported. The reported data indicate a possible phase transition at about 150 K for the trigonal RbIn(WO4)(2) chromium (III) doped crystals. The possible application of these crystals as laser systems is discussed.