A study of exchange interaction in Cr3+-doped CaY1-xGdxAlO4

The broadening of the R1 lines of Cr3+ impurity ions in the substitutionally disordered crystals CaY1-xGdxAlO4 (x=0, 0.1, 0.5, 1) has been studied. Fluorescence line narrowing removes the inhomogeneous broadening created by variation in the crystal field and results in instrument-limited spectral features for x=0 and 0.1. Exchange interactions between Cr3+ ions in octahedral positions and Gd3+ ions at second-nearest-neighbour sites cause significant broadening of the narrowed R1 line when x = 0.5 and 1. Comparisons of experimental and simulated spectra have been used to estimate the magnitude of the exchange-coupling constant, J approx. = 2-3 cm-1. Such simulations also show that the selection rule for the 2E→4A2 transition is broken by the Gd3+ spin in the Cr3+-Gd3+ exchange system. (author)