Luminescent Associates of Pb²⁺v_c⁻ Dipoles with Interstitial Iodine Atoms in KI:PbI₂ Crystals

Abstract

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.