SPECTRAL HOLE BURNING AT 183-K IN A CHEMICALLY DISORDERED RARE-EARTH COMPOUND

The rare-earth compound BaFCl0.5Br0.5:Sm2+ represents a new type of material in between the crystalline and glassy state. The Br and Cl ions randomly occupy the Cl-sites around the Sm2+ impurity so that this material exhibits microscopic disorder in spite of a definite lattice structure. The inhomogeneous line width of the 7F0-5D2-transition of Sm2+ is 38 cm-1 and was found to be independent of temperature between 1.5 and 77 K. Using high resolution laser-spectroscopy we have burnt permanent spectral holes in the inhomogeneous absorption line. The hole width is 86 MHz at 1.5 K and increases to 10.7 GHz at 77 K, so that 50-100 permanent holes could potentially be burnt simultaneously at liquid nitrogen temperatures. Gating light from the 5145 angstrom Ar+ line enhanced the hole-burning efficiency by a factor 3. Holes could be erased by illuminating the sample with 4880 angstrom blue light. The hole position as a function of temperature follows a T4 power law, encountered also in homogeneous crystalline systems. The coupling constant, however, was found to be four times smaller than in comparable homogeneous crystalline hosts and is rather comparable to the values measured in glassy systems. In lower spectral resolution (almost-equal-to 0.5 cm-1) holes could be burnt and directly detected up to 183 K, the highest temperature where the phenomenon of spectral hole-burning has yet been observed.