Optical properties of chromium(III) in trigonal KAl(MoO4)(2) and monoclinic NaAl(MoO4)(2) hosts

Infrared, Raman, absorption, excitation and emission spectra as well as ele ctron spin resonance spectra were measured For KCrxAl1-x(MoO4)(2) and NaCrx Al1-x(MoO4)(2) crystals (x varies from 0% to 2%) at temperatures ranging Fr om 15 to 300 K. A very rich vibronic structure of the emission band was exp lained and assigned to the respective vibrational modes. One Cr3+ center ch aracterized by 2.1 and 2.8 ms lifetimes (at 15 K) for the sodium and potass ium derivative, respectively, for the (2)(E) --> (4)A(2) transition was ide ntified for both the crystals. The phase transition from trigonal to monocl inic space group was discovered at about 60 K for KAl(MoO4)(2) : Cr3+ cryst al. The local structure of the Cr3+ surrounding is discussed in terms of th e spectroscopic results and the crystal field parameters are derived for bo th the materials. (C) 2001 Elsevier Science B.V. All rights reserved.