Optical absorption and EPR spectra of Li,SO, H,O crystals doped with Cr3+ are studied at liquid nitrogen temperature. The bands are found in absorption spectra with maxima about 17 000, 23 800 and 37 200 cm-I, assigned to the "A, -. 4T,, "A, -. "TI and 4A, -c 4T1 ("P) transitions, respectively. The crystal field theory parametem were determined and appeared to be as follows: Dq = 1700 cm-', B = 667 cm-', C = 3002 cm-I.The lines resulting from Cr3+ ions are found in EPR spectra. All lines are doublets, which is indicative of presence of two magnetically unequivalent centre positions, and have the hyperfine structure resulting from interaction of the unpaired electron spin with CrS3 isotope nucleus. Centres are oriented in such a way, that z-axes, corresponding to two centre positions, are situated a t both sides of maxis a t an angle of about 3'. Spin Hamiltonian parameters were found as follows: gz = 1.985, gu = 1.984, gz = 1.988, D = 0.130 cm-I,

LEHMANN (1983) commented on our "Paramagnetic Centres in X-irradiated LiNaSO, Single Crystals" (ALYBAKOV et al. 1981). We want to reply to these comments. As additional experimental data given below show, there is no error in the presentation of our experimental results.As it was noted earlier (ALYBAKOV et al. 1981), EPR spectrum of X-irradiated LiNaSO, crystal, measured at room temperature (RT) for arbitrary crystal orientations, shows 7 lines -A, -4, B, ,2, and C. Investigation of anguIar dependences at RT shows that A, -, and B1,2 lines indeed merge into one line for H 11 c. But spectrum changes gradually when cooling. Spectra, taken for two crystal orientations during the gradual cooling from RT to liquid nitrogen temperature (LNT), are shown in Figure 1. (It should be emphasized that spectra for each orientation were measured without any change of the crystal position).Spectrum, taken at RT for H 11 e, shows two lines: high-field intensive C-line and low-A3,4* Bl,.?A 1-0 + B y Fig. 1. EPR spectra of X-irradiated LiNaSO, crystal, measured at RT (l), -100 "C (2), -150 "C (3). and LNT (4)

Lasers, tunable in IR-region, are created on colour centers of alkali halides. Efficiency of such lasers depends essentially on the presence of the hydroxyl ions (OH-) in the crystals (GELLERMAN et al. ; MOLLENAUER). That is due to the fact that irradiation results in destruction of OH-ions with creation of various oxygen and hydrogen centers (KERKHOFF et al. ; AKHVLEDIANI, POLITOV), exerting essential influence on both formation and stability of colour centers. The main hydrogen centers in alkali halides are interstitial ions H; and atoms HP ( U , and U, centers, respectively) and hydrogen ions H-in the anionic sites (Ucenters). Besides, there were found hydrogen defects of fourth type, being neutral atoms H" in the anionic sites (HAYES, HODBY); these defects, called U,-centers, are present in small amounts.It is found that ¢ers in potassium halides are stable only at the low temperatures (below 100 K) (KERKHOFF et al.); heating leads to this center decomposition with U-and Fcentre creation. In neutr9n-irradiated LiF :OH-crystals hydrogen atom centers behave during the heating in a different way (KAMIKAWA); their concentration begins to increase above 150 "C, reaches the maximum at 270 "C, and then decreases monotonously. To elucidate whether this anomal change of the concentration of hydrogen atom centers is a distinctive feature of LiF :OH-crystals or it is characteristic of neutron irradiation only, investigations are needed to be carried out with use of other types of ionizing radiations. In this work we present the results of EPR study of thermal' destruction of the centers due to hydrogen atoms in LiF: OH-single crystals X-irradiated at room temperature. Investigated crystals were grown by Kyropoulos method in a platinum crucible from LiF of special purity doped with 5 mol% of LiOH. The samples were X-irradiated at room temperature for 5 h (tungsten target tube operated at 55 kV, 10 mA). IR absorption spectra were measured on UR-20 spectrophotometer. EPR spectra were recorded on standard X-band radiospectrometer RE-1307 provided with thermostating block. When studying the thermally induced decay of paramagnetic centers, the sample was heated in the cavity by the flow of heated nitrogen steams. Spectra were recoTded after the sample keeping for 10 min at each temperature. In a control experiment the sample was heated in a furnace.IR absorption spectrum of unirradiated crystal shows the band at 3728 cm-' due to OH-local vibrations. X-irradiation results in weakening of absorption at 3728 cm-' ; that is indicative of photochemical decomposition od hydroxyl ions, which may occur according to the following reaction :OH-% 0-+ Ho .

The EPR and optical absorption spectra of paramagnetic centers produced by X-irradiation in LiNaSO, single crystals were investigated. 7 EPR lines are observed a t room temperature and 6 more lines -a t LNT. The angular dependences of line positions at LNT are studied and the principal g-factor values are defined. The comparison with published data permitted to assign six the most anisotropic lines to ion-radical SO, with different orientations in the lattice; two lines to ion-radical SO;; slightly anisotropic doublet line -to 0; ozonide ion; isotropic line with g = 2.0045 -to ion radical SO;.UCcJreAOBaHbI CIIeKTpH 3nP ki OIITHYeCKOrO nOrJIOIqeHHtI IIapaMarHHTHbIX UeHTpOB, C03AaHHhIX PeHTreHOBCKHM 0 6 n y s e~u e~ B MOHOKpACTaJIJIaX LiNaSO,. npH KOMHaTHOB TeMnepaType ~a 6 n m~a e~c~ UcaenosaHM ymosrae ~~B H C H M O C T H nonomenm