Studied ZnSe samples were grown by physical vapor transport method and doped with ytterbium during the growth process. Photoluminescence (PL) was excited with modulated laser emission with the wavelength of 532 nm and average power ~160mW. Mid-IR PL spectra were registered with PbS photoresistance. Experimental data were collected in automaton mode. In Fig.1 the mid-IR PL spectra of the ZnSe:Yb crystals versus the growth temperature for as-grown samples (a), treated in Zn vapor (b) or Se vapor (c) media are presented. PL band located in 1950nm region is associated with intrashell transitions within Cr2+ ion between the ground and first excited states (5E and 5T2 respectively) [1]. The chromium presence in the samples may be explained by the fact that transition metals are typical background impurities for the zinc chalcogenides crystals [2]. Energy position of the PL band with maximum located near 1650 nm is close to distance between Cr+ and Cr2+ energy levels in zinc selenide (~0,7eV [3]), this band's intensity increase observed in the case of annealing in Se vapor media (Fig.1c) may be caused by interaction of the Yb doping impurity with Cr background impurity in crystal lattice nodes. It is known that interstitial site rare-earth ion 3+ charge state leads to a local charge disbalance. It was shown that electroneutrality may be reached by replacement of the first order neighbors (Zn2+ ions in the lattice nodes) with single charged ions (in particular with Cu+ or Ag+ [4]). May be presupposed that a similar case is possible with chromium: in the growth process ytterbium impurity incorporates in the interstitial sites of the crystal lattice locating around itself chromium impurity and forming a cluster. Chromium ions placed in crystal lattice nodes, that have 2+ charge in the ytterbium absence, obtain 1+ charge state and may compensate local charge disbalance. This leads to decrease of the Cr2+ ions concentration and decrease of the 1950 nm band's intencity (Fig.1а). Increase of the 1950 nm band intensity (relative to 1650 nm) after the annealing in Zn vapor medium may be explained be the Yb3+ local charge compensation by interstitial zinc (Fig.1b).figureFig. 1. mid-IR PL spectra of ZnSe:Yb crystals measured at Т=85К. а) as-grown, b) annealed in Zn vapor media, c) annealed in Se vapor media [1] I.T. Sorokina. Optical Materials, 26, 2004, pp.395-412 [2] H. Przybylinska et al. Phys. Rev. B, 40 (3), 1989, pp.1748-1755 [3] V.Gavriushin, A.Kadys, M. Sudzius, K. Jarasiunas.JETP Letters, 83 (1), 2006, pp. 22-27. [4] Kingsley, M.Aven. Phys. Rev., 155 (2), 1967, pp.235-246. This work was supported by Academy of Science of Moldova grant 11.817.05.11F