Optical properties of Yb 3+ ions in Ca x Cd 1-x F 2 (x = 0.30) crystals are investigated. Photoluminescence and absorption spectra of the intra-ion transitions were measured in a wide temperature range (4 - 300 K). It was found that position and shape of the Yb 3+ zero-phonon emission lines exhibit a noticeable temperature dependence, particularly at temperatures T < 50 K. In the same temperature limits, the position and the shape of the Yb 3+ zero-phonon absorption lines do not change significantly. It was found that the measured shift between energy of the emission and absorption zero-phonon lines is due to the efficient energy migration among the Yb 3+ ions.