Research on the thermal shifts and electron-phonon coupling parameters of R-line for Cr3+ and Mn4+ ions in YAlO3 crystals

The thermal shifts of R-line for isoelectronic 3d(3) ions Cr3+ and Mn4+ in YAlO3 crystal are studied by using a new theoretical expression including both the static contribution due to lattice thermal expansion and the vibrational contribution due to electron-phonon interaction. The new expression in form is almost the same as that containing only the vibrational contribution (which is widely-used in the previous papers) except the change of coefficient from alpha to alpha' + A (where alpha, obtained from the old expression, and alpha', obtained from the new expression, are the apparent and true electron-phonon coupling parameters, respectively. A is a parameter concerning the static contribution). By using the new expression and the analysis of pressure- and temperature-dependences of R-line, it is found that the static contribution to the thermal shift of R-line in sign is contrary to and in magnitude is about 36% of the vibrational one. Thus, the electron-phonon coupling parameters alpha' increase about 36% compared with the corresponding parameters alpha for both Cr3+ and Mn4+ in YAlO3 crystal. So, for the reasonable explanation of thermal shifts of spectral lines and the determination of the true electron-phonon coupling parameter, both the static and vibrational contributions to thermal shift should be taken into account. The reason that the electron-phonon coupling parameter vertical bar alpha'vertical bar of Mn4+ is larger than that of Cr3+ in YAlO3 crystal is discussed. (C) 2013 Elsevier B.V. All rights reserved.