Anomalous discrete disorder response of high-symmetry impurity centers spectra in garnet solid solutions
The zero-phonon electronic transitions in Cr3+ and Ce3+ impurity ions in a series of Lu3xY3−3xAl5O12 (0 < x < 1) garnet solid solution crystals were studied experimentally. It was observed that in contrast to the case of Ce3+, the modification of zero-phonon R-line (2E–4A2) fluorescence spectra of Cr3+ ions with changing x occurs in a discrete fashion and is not accompanied by strong inhomogeneous broadening, as usually happens in solid solutions. The effect is ascribed to the high C3i symmetry of the Cr3+(Al3+) sites that allows only a limited number of non-equivalent Cr3+ centers in a mixed environment. The energies and radiative lifetimes of the 2E states of locally identical Cr3+ centers inside different mixed garnet matrices were studied and the observed dependences on the Lu content x are discussed in terms of lattice compression and dilation.