The absorption spectra, emission under 940 nm excitation by laser diode, and fluorescence lifetimes of as-grown and annealed Cr,Yb:YAG crystal have been investigated at room temperature. The increase of absorption coefficients at 941 and 1030 nm and the quenching of Yb3+ emission intensity and fluorescence lifetime after annealing are due to the increase of the concentration of Cr4+ ions. The data of thermal expansion and specific heat of the crystal have been measured. The thermal expansion coefficient is alpha = 8.71 x 10(6) /K. The specific heat is 89.9 cal/mol K at 320.5 K. (C) 2003 Elsevier B.V. All rights reserved.