Origin of the Luminescence Bands in PbCl₂Crystals Induced by UV Light at Low Temperatures

Abstract

Four luminescence bands are observed in PbCl 2 at low temperatures. The excitation spectra for these bands have been measured in order to clarify their origins. The 3.76 eV (UV) and 2.88 eV (B) bands are eciently excited with photons in the region of the lowest exciton band. We attribute both bands to radiative decay of an exciton self-trapped at Pb 2þ ion site. The 2.62 eV (BG) band is excited in the region above the band gap, in which the Pb 3þ 2 self-trapped electron (STEL) center can be produced. The BG band also appears in afterglow and photostimulated luminescence spectra. From these results, it is supposed that the BG band is related to Pb 3þ 2 (STEL) centers and self-trapped hole centers. The 1.88 eV (R) band is excited even in the energy region lower than the lowest exciton band, and is thus connected to an extrinsic lattice imperfection.

Formation of Cs3Cu2I5 microcrystals in CsI crystals through the aggregation of Cu+ ions

“…22) Similar STEs were observed in AgCl, TlCl, and PbCl 2 that have band gaps of 3-4 eV. [23][24][25] Here, the authors should point out that the present study shows that the two PL bands at 415 and 440 nm were observed in the Cs 3 Cu 2 I 5 bulk crystals, although the previous studies by the other researchers have reported only the PL band at 440 nm in Cs 3 Cu 2 I 5 thin crystals. 11,12) Since the difference in the PLE spectra for the two PL bands indicates the presence of two types of relaxation pathways, we can infer that the two PL bands result from two types of the lattice configurations of STEs, which may be related to two different Cu + ion sites in the Cs 3 Cu 2 I 5 crystal lattice: the planar 3-fold and tetrahedral coordinations.…”

Exciton-relaxation dynamics in lead halides

“…The PL components have been assigned to STE lumines-PL Intensity (arb. units) cence by many researchers [1,12,19,20,21,22,23]. However, the stable range disagrees with that of self-trapped states in each crystal: In cubic PbF 2 , the PL component at 4 eV is quenched around 30 K [1,21] while the STHs are bleached around 175 K [18].…”

Self-trapped states and related luminescence inPbCl2crystals

“…39 As the origins of the UV-PL band at 3.76 eV and the blue-PL band at 2.88 eV, the self-trapped excitons (STE's) with the configuration of (Pb + + hole) were proposed, and the origin of the BG-PL band was attributed to the STE's of (Pb 2 3+ + hole). 15,16,17 The models claim that the lowest excitons and free e-h pairs relax into different localized states. However, the Pb + centers in PbCl 2 have not been reported.…”