Spectroscopy of the <i>n</i>s<sup>1</sup>‐Centers in Ionic Crystals

Nistor, S. V.; Schoemaker, D.; Ursu, I.

doi:10.1002/pssb.2221850102

Cited by 47 publications

(40 citation statements)

References 182 publications

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“…The hole can be trapped at either oxygen (O -center) or lead (Pb 3 + center). The hole trapped at oxygen near impurity was observed in ZnWO4 [12], whereas self-trapped hole forming Pb 3 + center was observed in PbF2, PbCO3, and BaPbF6 [13]. Thus we suggest that two types of the self-trapped holes in PWO are possible -as O -center and as Pb 3 + center.…”

Section: Resultsmentioning

confidence: 72%

The Model for Luminescence Center Excitation in PbWO₄

et al. 1999

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The luminescence and transient absorption of PbWO 4 crystals were studied. The electron beam (10 us, E 270 keV) was used as excitation source. The kinetics of luminescence is complicated -the prompt rise of luminescence intensity is followed by a slow (r, 100 ns) rise. The luminescence decay at 80 K is nearly exponential with rd 4.0-4.5 μs. The decay kinetics of transient absorption at 3.5 eV can be described roughly by two exponents with time constants r 1 Ń 100 ns and 7-2 4.0 μs. A common process responsible for absorption relaxation and luminescence rise is suggested. The luminescence center excitation occurs during recombination process via Pb2+ excited state formation and subsequent energy transfer to WO4 -group.

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Section: Resultsmentioning

confidence: 72%

The Model for Luminescence Center Excitation in PbWO₄

et al. 1999

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“…This conclusion is also supported by the experimental hyperfine constant of the Ag 0 center in SrCl 2 , which for the 107 Ag isotope is A ϭ1153 MHz. 62 In fact that figure is significantly smaller than the A values measured for the cationic Ag 0 center in alkali halides 14,17 and involves a reduction factor of 67% with respect to the hyperfine constant of the free Ag 0 atom. By contrast it is much closer to A( 107 Ag)ϭ1256 MHz reported 17 for an Ag 0 atom formed at an anion site in KCl.…”

Section: The Stability Of the Localized Ag 0 Center In Other Latticesmentioning

confidence: 90%

“…The formation of such neutral species has been proven by means of EPR and electron-nuclear double resonance techniques, [12][13][14][15][16] their main properties have been reviewed by Nistor, Shoemaker, and Ursu. 17 The experimental hyperfine constant A of KCl:Ag 0 is practically equal to that for the free silver atom A 0 . 12,14,16 In particular, A is found to be only about 5% smaller than A 0 , which is 1718 MHz for the 107 Ag isotope.…”

Section: -11mentioning

confidence: 94%

“…This high localization of the electronic charge on the Ag 0 atom at the equilibrium distance turns out to be in reasonable agreement with the ratio between the experimental hyperfine constants of the 107 Ag isotope for the KCl:Ag 0 system (Aϭ1638 MHz) and the free-atomic isotope (A 0 ϭ1718 MHz). 12,14,16,17 The small reduction undergone by A with respect to A 0 can be ascribed to the fraction of the electronic charge lying out of the silver because in a first approximation Aϭ f Ag A 0 .…”

Section: ͑1͒mentioning

confidence: 99%

“…Another support to this conclusion comes from the temperature dependence of the hyperfine constant A, which shows a linear decrease in the 77-300 K temperature range. 15,17 In fact, as the mechanisms involving a phonon of frequency ⍀ includes the factor coth(ប⍀/2KT) the observed temperature dependence of A requires that ⍀ be smaller than ϳ110 cm Ϫ1 . Other evidence, though indirect, about the proper value of A , comes from the analysis of the experimental bandwidth of the charge-transfer transition of the KCl-Ag 0 center.…”

Section: ͑7͒mentioning

confidence: 99%

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Neutral atoms in ionic lattices: Stability and ground-state properties ofKCl:Ag0

et al. 2000

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The equilibrium geometry of Ag 0 centers formed at cation sites in KCl has been investigated by means of total-energy calculations carried out on clusters of different sizes. Two distinct methods have been employed: First, an ab initio wave-function based method on embedded clusters and second, density-functional theory ͑DFT͒ methods on clusters in vacuo involving up to 117 atoms. In the ab initio calculations the obtained equilibrium Ag 0 -Cl Ϫ distance R e is 3.70 Å, implying a large outward relaxation of 18%, along with 7% relaxation for the distance between Ag 0 and the first K ϩ ions in ͗100͘ directions. A very similar result is reached through DFT with a 39-atom cluster. Both approaches lead to a rather shallow minimum of the total-energy surface, the associated force constant of the A 1g mode is several times smaller than that found for other impurities in halides. These conclusions are shown to be compatible with available experimental results. The shallow minimum is not clearly seen in DFT calculations with larger clusters. The unpaired electron density on silver and Cl ligands has been calculated as function of the metal-ligand distance and has been compared with values derived from electron-paramagnetic resonance data. The DFT calculations for all cluster sizes indicate that the experimental hyperfine and superhyperfine constants are compatible when R e is close to 3.70 Å. The important relation between the electronic stability of a neutral atom inside an ionic lattice and the local relaxation is established through a simple electrostatic model. As most remarkable features it is shown that ͑i͒ the cationic Ag 0 center is not likely to be formed inside AgCl, ͑ii͒ in the Ag 0 center encountered in SrCl 2 , the silver atom is probably located at an anion site, and ͑iii͒ the properties of a center-like KCl:Ag 0 would experience significant changes under hydrostatic pressures of the order of 6 GPa.

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