No abstract

EPR-spectra of X-irradiated potassium dichromate crystals are studied a t various temperatures froin RT to LNT. The most intensive lines are interpreted as due to radicals Cr0:-(A-lines) and CrO; (C-lines), resulting from Cr,O, owing to X-irradiation. Hyperfine structure of C-line, due to interaction of unpaired electron with Cr53 nucleus, occurs at low temperatures, and new unobserved earlier Q-lines appear near-by C-line. The spectrum

on the occasion of his 75th birthday EPR, optical, and IR absorption spectra of X-irradiated KCl crystals doped with K,CrO, and K,Cr,O, are studied. It is ascertained that the impurity enters as chromate in both cases and there are two centre typesisolated Cr0:-ions and (3-05-ions coupled with divalent cation impurities. The X-irradiation results in the formation of paramagnetic Cr0;centres with monoclinic local symmetry C,, whose excessive negative charge is compensated by an anion vacancy. The EPR spectrum due to these centres is described by a spin-Hamiltonian for S = 1/2 with g, = 1.948, gl/ = 1.953, g, = 1.967. The x-axis of the g-tensor is oriented along <001) and two other principal axes along the directions of (110) type. MCCJIeAOBaHbI CIIeHTpbI 3nP, OIITM9eCIEOrOH MH@paKpaCHOrO IIOrJIOIUeHHFI 06JIy9eHHbIX HpHCTaJIJlOB KC1 C IIpHMeCRMH K,CrO, M K&kzo7. YCTaHOBJIeHO, 9 T O B 0 6 0~~ CnysaRx npHMeCb BXOAHT B BHAe XpOMaTa, IIpHseM CyIIIeCTByXOT ABa THIIa UeHTPOB -H3OJIHpOBaH-HbIe HOHbI cl'oi-H HOHbI CrO;--, CBR3aHHble C AByXBaneHTHOfi IEaTMOHHOB IIpHMeCbIo. MOHOKJlHHHOfi JIOIEaJIbHOfi CHMMeTpHefi c,, M36bITOWIbIfi OTPHUaTeJIbHbIfi 3apFIn KOTOpbIX KOMIIeHCHpOBaH aHHOHHOfi BaKaHCHea. 06yCJIOBJIeHHbIi% MMIl CIIeKTp 3nP OIIHCbIBaeTCII CIIHH-FaMHJlbTOHHaHOM AJIR 8 = 112 C 9, = 1,948, gv = 1,953, g, = 1,967. OCb Z 9-TeH3Opa OpHeHTMpOBaHa BAOJrb ( O o l ) , a HBe HpJTHX rJlaBHbIX OCH -BAOJIb HaIIpaB-B p e 3 y m~a~e 06~1yse~nn B KpacTamax C O~D~I Q T C~ napaMarHmHbie UeHTpbI CrOl-c JIeHnii THna (110).

The thermoluminescence (TL) of pure and doped NaF crystals has been intensively investigated for the last years, however, in many works the spectral distribution of the emission was not studied and the interpretation of the glow peaks is often contradictory /l/.This note gives some new results concerning the influence of oxygen ions o n the T L process. N a F single crystals were grown both in vacuum and air atmosphere from the reactive of high purity. All the samples were X-irradiated up t o l x l 0 R. The absorption spectra were measured on a Unicam SP8-100 spectrophotometer. Cooled photomultipliers sensitive in the range of 180 t o 800 nm were used while studying the TL; the constant heating rate was 1 0 K/min. The spectral composition of the emission was analysed using a MDR-2 monochromator. (Fig. 1); these bands are ascribed to O--V: complexes. At LNT there is also an absorption band a t 196 nm, conditioned by 0--ions. N a F ( 0 2 ) samples (NaF(vacuum), subjected to a prolonged thermal treatment in the air) show new absorption bands at 255 and 3#55 nm (curves 3 and 4 in Fig.

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)