Electron-phonon coupling of Cr3+ doped garnets

The electron-phonon coupling for the E-2 --> (4)A(2) transition on Cr3+ has been determined for different chromium doped garners by measuring the rati o between vibronic and zero-phonon line intensity, and by performing temper ature dependent line broadening and line shift measurements. It was found t hat the electron-phonon coupling for the transition is dependent on the cov alency of the host lattice: due to the difference in covalency the electron -phonon coupling for a gallate lattice (e.g. Y3Ca5O12) is higher than the a luminate lattice (e.g. Y3Al5O12). Measurements on the dependence of electron-phonon coupling on the size of t he site for which Cr3+ substitutes indicate that the value of the electron- phonon coupling parameter alpha (determined from temperature dependent line shift measurements) is lower for garnets where Cr3+ resides in the smaller Ga3+- and Al3+-sites (e.g. Y3Al5O12 and Y3Ga5O12) than for the garnets wit h Cr3+ on a bigger Sc3+-site (e.g. Y3Sc2Al3O12 and Gd3Sc2Al3O12. (C) 2000 E lsevier Science Ltd. All rights reserved.