No abstract

Associates of Cu° atoms with anion vacancies v a+ (Cu°v a+centres) are used as luminescent detectors for the study of anion vacancy mobility in KCl crystals. It is found that near 220 K, Cu°v a+ centres may be thermally formed because of the migration of v a+ only to its neighbouring Cu° atom (i.e. the process occurs in {Cu°–v a−} pairs). An analogous process in {Cu+–v a+} pairs results in the creation of Cu+v a+ centres. After Cu+v a+ have trapped electrons released at the thermal destruction of Cu°, Cu°v a+ centres are formed. {Cu+–v a+} and {Cu+–v a+} pairs are produced at low temperatures by the transfer of an F electron onto an impurity ion in irradiation‐generated {Cu+–F} and {Cu2+–F} pairs. If the crystal contains Cu a− centres, Cu°v a+ centres may be formed at T > 370 K by the interaction of mobile VF centres, produced at a thermal dissociation of Cl3 molecular ions, with Cu a− centres. It is proposed that at T < 300 K it is not the isolated but the “associated” anion vacancy that can migrate. This process occurs in the field of some defects and needs a comparatively lower activation energy than the motion of isolated v a+. The isolated or “free” v a+ which are believed to be mobile at higher temperatures, are practically absent in X‐irradiated crystals at T > 250 K due to the interaction of v a+ with mobile cation vacancies or interstitial halide ions as well as due to the thermal association of v a+ with neighbouring lattice defects.

Two infrared emission regions (with maxima at 0.803 and 0.723 eV) recently observed by Harami et al. in X-irradiated K I : PbI, and the emission regions with maxima at 2.01, 1.79, and near 1.2 eV are studied. The observed emission bands are connected with H,(Pb2+j centres (Pb2+ ions associated to molecular ions on anionic (a) and cationic (c) sites). The infrared emission bands of these centres are due to processes occuring in the excited state of the molecular ion perturbed by the P b Z + ion. The emission bands are connected with electronic transitions from the tetragonal (2.01 and 1.79 eV peaks) and trigonal (region around 1.2 eV) minima of the triplet relaxed excited state of the P b Z + ions perturbed by the ion which can occupy two different positions with respect to P b Z + . The emission band with maximum at 2.05 eV and the region near 1.2 eV are associated to similar transitions in the Pb2+ ion perturbed by the [131aFa (V,,(PbZ+) centres) molecular ion. On the basis of these results the optical properties of V, centres (at 0.805 and 0.734 eVj, previously observed by Harami et al. in halogen-excess K1 crystals, and assumed here to be the [lilac molecular ions, are also discussed. nOKa3aH0, YTO nBe IIOJIOCbl HH@paKpaCHOro H3JIyYeHHR (C MaKCHMYMaMH IIPH 0,803 H 0,723 CV), HenaBHO 06HapyXeHHbIe XapaMH C COTPYAHKKaMH B 06JIYYeHHbIX PeHTreHOBCKHMM JIyYaMM KpHCTan-JIaX KI PbI,, H IIOJIOCbI H3nyYeHKR C MaKCHMyMaMH IIpH 2,01, 1,79, B OK0,lO 1,2 e v , HCCJIe-nOBaHHble B HaCTORWefi pa6OTe. 06yCJIOBJIeHbI Hz(PbZ +)-UeHTpaMH (aCCOUHaTaMK KOHOB PbZ + C MOJIeKYJXPHbIMH HOHaMH 3aHHMaH)WKMH aHHOHHblfi (a) 11 KaTHOHHblfi (C) y33bI). MH-@paKpaCHOe H3JIYYeHHe 3THX UeHTpOB CBR3blBaeB.rCR C npOUeCCaMM, IIpOHCXO.4RIUBMH B B036YXUKHHOM COCTOXHHH MOJIeKynRpHOrO HOHa B~nHMoe H3JIyYeHHe HX CBRSbIBaeTCR C 3JIeKTPOHHbIMM IIepeXOflaMH H 3 TeTparOHaJIbHbIX (nOJIOCbl 2.01 H 1,79 e v ) H TPHrO-HanbHblX (IIOJIOCbl OKOJIO 1.2 e v ) MHHHMYMOB TpHIIJIeTHOrO peJIaKCHpOBaHHOJ0 B036YXneHHOTO COCTORHHR HOHa Pb2+, B03MYLUeHHOTO HOHOM [I,],,, KOTOPblk MOXeT 3aHHMaTb nBe pa3JIHYHbIe I I 0 3 H I p f H IIO OTHOUIeHHIO K Pb2+. n O J I O C b 1 H3JIyqeHHR C MaKCHMYMaMH IIpH 2,05 eV A B O~J I~C T H OKOJIO 1.2 eV IIpHIlHCbIBaKlTCR aHaJlOrHYHbIM IlepeXOnaM B HOHaX P b 2 + , B03MYUleHHblX MOJe-KynRpHblM HOHOM [1,],,, (VzZ(PbZ +) UeHTpaX). O 6 c y~n a e~c a IIpHpOfla Ha6~7IOfl2IBItIefiCR PaHee Xapa-MI1 C COTPYAHHKaMH HH@PaKpaCHOfi JIIoMHHeCIIeHUHH (0,805 H 0,734 e v ) T.H. VL-UCHTPOB, OnTHYeCKM CO3AaBaeMbIX B KpHCTannaX KI, anLIHTHBHO OKpaLLIeHHbIX B IIapaX fiona. BO3MyLUeHHOrO HOHOM Pb2 +. l ) U1.

Several types of luminescent associates of lead ions (Pb2+, Pb+) with interstitial halide ions (X−i) as well as with cation (v−c) and anion (v+a) vacancies are observed in alkali halides X‐irradiated at 80 or 295 K. Optical properties and a detailed structure of these associates, the processes of their creation and destruction as well as their optically or thermally stimulated transformations are studied. The associates investigated form the three following groups each containing several types of centres: (1) centres on the basis of a PbX 2−‐molecular ion; (2) centres on the basis of a Pb2+X 2− dipole; and (3) centres of the laser‐active structure on the basis of a Pb+X−v+a associate. The optical characteristics of the various centres of each group are shown to be similar. It is concluded that they are determined by electronic transitions between the energy states of the basis associate (PbX 2−, Pb2+X i−, or Pb+X−v+a), and that the influence of some other defects (v c−, X i−, X3, etc.) may be considered as a small perturbation.