Abstract:Host luminescence excitation spectra and reflection spectra of and crystals at low temperatures have been measured in the energy region of 4-30 eV using synchrotron radiation. High-efficiency host luminescence is connected to radiative decay of self-trapped cation excitons. It is shown that also in the region of excitation multiplication, e.g. if the excitation energy is larger than twice the band gap energy , and in the relaxation process of core excitons the radiative self-trapped cation excitons are forme… Show more
“…This emission is excited in the region of the cation exciton absorption band, corresponding to the transition of 1 S 0 -3 P 1 of Pb 2+ . The similar cation exciton emission peaking at 3.8 eV with the exciton excitation of 4.7 eV at 8 K in PbCl 2 was also reported [13]. From the reflection and excitation spectra of PbFCl, the cation exciton absorption peaking at 247 nm was observed.…”
“…This emission is excited in the region of the cation exciton absorption band, corresponding to the transition of 1 S 0 -3 P 1 of Pb 2+ . The similar cation exciton emission peaking at 3.8 eV with the exciton excitation of 4.7 eV at 8 K in PbCl 2 was also reported [13]. From the reflection and excitation spectra of PbFCl, the cation exciton absorption peaking at 247 nm was observed.…”
“…It has been concluded in [4,7,12,13,18] that these bands belong to the self-trapped cation excitons (STE). (However, some authors do not connect the B band with the STE, see, e.g., [15,16,22,24].)…”
Section: Discussionmentioning
confidence: 99%
“…In [19], the structural model has been proposed for the STE of the first type: this is the {Pb þ (X --) 3 þ hole}-type STE (see also [28,39]). As both types of emissions can be excited by Xrays [25] and in the band-to-band transitions region [7] (see also Figs. 1a and 1b), the STEL of the Pb þ -and (Pb 2 ) 3þ -types should be detected in PbCl 2 by the ESR method.…”
Emission and excitation spectra, and the luminescence decay kinetics have been studied for PbCl 2 crystals at the temperatures 0.45-100 K. It has been found that even at the lowest temperatures, where the non-radiative decay of exciton states in PbCl 2 does not take place, the decay times of both the ultraviolet (UV) and the blue (B) exciton emission are by a few orders of magnitude shorter than the decay times of the emission arising from the triplet relaxed excited state of Pb 2þ centres in lead-doped ionic crystals. A conclusion has been drawn that the luminescence of lead halides cannot be connected with single Pb 2þ ions. It is proposed that the radiative decay of the self-trapped excitons of the type of {(Pb 2 ) 3þ þ hole} is responsible for the UV and the B emission of PbCl 2 crystals, while the lowest-energy (BG) emission arises from the tunnelling recombinations between the (Pb 2 ) 3þ -type self-trapped electrons and V K -type self-trapped holes.
“…[2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17] They are also attractive materials for practical use, e.g., as a scintillating substance (PbF 2 ) ͑Ref. 2͒ and as acousto-optical crystals (PbCl 2 and PbBr 2 ) ͑Refs.…”
Polarized reflectivity spectra of single crystals of ␣-PbF 2 , -PbF 2 , PbCl 2 , and PbBr 2 have been measured at 10 K in the energy range up to 30 eV using synchrotron radiation as a light source. The spectra are well resolved in comparison with those reported previously. Optical constants have been derived through the Kramers-Kronig analysis. The effect of phase transition on the optical spectra of PbF 2 is also examined. With use of the discrete variational X␣ method, the electronic structures of the clusters consisting of a Pb 2ϩ ion and neighboring halogen ions have been calculated for better understanding of the optical properties of Pb halides. The calculation indicates that the lowest excitons in all lead halides are attributed to the cationic transitions. The electronic structures of lead halides are discussed on the basis of a comparison of experiment and calculation.
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