Exciton Emission in LaF&lt;sub&gt;3&lt;/sub&gt; Crystals

Раджабов, Е. А.; Nepomnyashikh, A.I.

doi:10.4028/www.scientific.net/msf.239-241.275

Cited by 3 publications

(3 citation statements)

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“…Assuming that the increase in the gap value is entirely due to downshift of the valence band, the valence band edge has the value of −9.6 eV, just above that of the largest nanocluster. However, the exact position of the edges and the value of the gap would be heavily affected by the disorder in the fluoride sublattice due to exceptionally low barriers for fluorine vacancy diffusion . As reported earlier, the nanocluster electron affinity is dependent on the average coordination of lanthanum and whether there is an exposed cation.…”

Section: Resultsmentioning

confidence: 85%

Knowledge Led Master Code Search for Atomic and Electronic Structures of LaF₃ Nanoclusters on Hybrid Rigid Ion–Shell Model–DFT Landscapes

Woodley

2013

J. Phys. Chem. C

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Stable and metastable atomic configurations of stoichiometric (LaF 3 ) n nanoclusters are obtained for n = 1 to 6 using Monte Carlo global optimization techniques implemented in newly developed software. All configurations are refined using an allelectron DFT approach with the PBEsol exchange and correlation functional. To reduce the computational cost, approximate configurations were initially filtered out using a basin hopping algorithm that was biased toward finding either the global minimum or all metastable minima on the six energy landscapes defined by interatomic potentials within a polarizable shell model. In both algorithms, standard local optimization methods are employed to relax trial random atomic configurations whereby the polarization of the ions is initially constrained to improve convergence to local energy minima. The global optimization routines were implemented within the in-house Knowledge Led Master Code (KLMC). Electronic characterization of the refined structures included the calculation of vertical ionization potentials and electron affinities using the ΔSCF approach at the PBEsol DFT level and the many-body G 0 W 0 /PBEsol0 theory which employs the hybrid density functional initial guess of the quasi-particle orbitals. The atomic structure of the nanoclusters can be seen to evolve with size from a trigonal pyramid to ring structures and finally to compact symmetrical configurations, where the coordination of higher charged La gradually increases. Additional fluorine ions are accommodated between two La ions: single fluoride (−F−) bridges are replaced by bridge pairs or trios, although more than three fluoride bridges between two cations are heavily penalized in energy and cluster ranking. There is also a trend for the external surface of LaF 3 nanoclusters to be decorated by singly coordinated fluorine anions, one per outer La ion for larger nanoclusters. For the global minimum (LaF 3 ) n nanoclusters, although the changes are modest, the ionization potential decreases, and the electron affinity increases with n, effectively decreasing the precursor of the band gap of the bulk phase. The majority of the metastable nanoclusters follows this trend, with the exception of configurations with at least one exposed cation at the surface which is not terminated by an anion. These nanoclusters have a greater electron affinity that could be attributed to structural features analogous to defects in solids.

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Section: Resultsmentioning

confidence: 85%

Knowledge Led Master Code Search for Atomic and Electronic Structures of LaF₃ Nanoclusters on Hybrid Rigid Ion–Shell Model–DFT Landscapes

Woodley

2013

J. Phys. Chem. C

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“…Excitation of the singly doped crystals with 308 nm laser light at room temperature produces colour centres by a two-photon process similar to those obtained with x-rays or γ -rays. The low-temperature thermoluminescence curves, created by VUV illumination or x-ray irradiation, are similar for Ce 3+ -doped CaF 2 , SrF 2 and BaF 2 [25].…”

Section: The Nature Of Eu 2+ -Related Transitions In the Vuv Regionmentioning

confidence: 80%

“…All of the above-cited papers show that in alkali halide crystals and in alkaline-earth fluoride crystals containing different impurities (Tl + , Pb 2+ , Ce 3+ ), during illumination with ultraviolet photons with energy lower than the energy of band-to-band transitions, trappedelectron and trapped-hole defects are created. In several papers it was assumed that impurity levels in the band gap were filled by electrons by a charge-transfer mechanism [20,[23][24][25]. However, in the case of BaFX:Eu 2+ we have shown that impurities assist in the creation of trapped electrons and holes.…”

Section: The Nature Of Eu 2+ -Related Transitions In the Vuv Regionmentioning

confidence: 99%

Photoionization processes in barium fluorohalide crystals doped with Eu²⁺

Раджабов¹,

Kurobori²

2001

J. Phys.: Condens. Matter

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The absorption, excitation and photostimulation spectra and thermoluminescence creation spectra of pure BaFX (X = Br, Cl) and BaFX:Eu2+ single crystals were studied in the vacuum-ultraviolet (VUV) region 5-10 eV at temperatures of 6-300 K. Creation of a VK thermoluminescence peak was observed when the BaFX:Eu2+ crystal was illuminated with VUV photons with energies above 6 eV while band-to-band transitions begin above 8-9 eV. Low-temperature photostimulation spectra for Eu2+ luminescence created by 6-7 eV photons show new bands in the infrared region, with intensities directly proportional to the Eu2+ concentration. However, the same infrared photostimulation bands for exciton luminescence were also observed for undoped crystals after x-ray irradiation. Therefore, a trace concentration of the shallow electron traps is present in each undoped and Eu-doped BaFBr and BaFCl crystal. The results show that self-trapped holes and electrons are trapped on different non-europium centres, created by VUV photons in BaFX:Eu2+ crystals at low temperature. It was concluded that Eu2+ ions assist in the creation of free electrons and self-trapped holes by photons with an energy 2-3 eV lower than those of band-to-band transitions.

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Energy transfer in inorganic scintillators

Belsky

Kamenskikh

Mikhaĭlin

et al. 1999

Radiation Effects and Defects in Solids

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Exciton Emission in LaF<sub>3</sub> Crystals

Cited by 3 publications

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Knowledge Led Master Code Search for Atomic and Electronic Structures of LaF₃ Nanoclusters on Hybrid Rigid Ion–Shell Model–DFT Landscapes

Knowledge Led Master Code Search for Atomic and Electronic Structures of LaF₃ Nanoclusters on Hybrid Rigid Ion–Shell Model–DFT Landscapes

Photoionization processes in barium fluorohalide crystals doped with Eu²⁺

Energy transfer in inorganic scintillators

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Exciton Emission in LaF<sub>3</sub> Crystals

Cited by 3 publications

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Knowledge Led Master Code Search for Atomic and Electronic Structures of LaF3 Nanoclusters on Hybrid Rigid Ion–Shell Model–DFT Landscapes

Knowledge Led Master Code Search for Atomic and Electronic Structures of LaF3 Nanoclusters on Hybrid Rigid Ion–Shell Model–DFT Landscapes

Photoionization processes in barium fluorohalide crystals doped with Eu2+

Energy transfer in inorganic scintillators

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Knowledge Led Master Code Search for Atomic and Electronic Structures of LaF₃ Nanoclusters on Hybrid Rigid Ion–Shell Model–DFT Landscapes

Knowledge Led Master Code Search for Atomic and Electronic Structures of LaF₃ Nanoclusters on Hybrid Rigid Ion–Shell Model–DFT Landscapes

Photoionization processes in barium fluorohalide crystals doped with Eu²⁺