Excitons trapped at impurity centers in highly ionic crystals

McClure, Donald S.; Pédrini, C.

doi:10.1103/physrevb.32.8465

Cited by 164 publications

(125 citation statements)

References 7 publications

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“…7 have demonstrated that when the lowest energy 5d state of Ce 3+ is located below but close to the conduction band minimum ͑typically 0.5-0.1 eV͒, the photocurrent intensity upon 5d excitation becomes strongly temperature dependent due to a thermally stimulated ionization process. Other studies [13][14][15] have shown that when the lowest energy 5d states are far below the conduction band minimum ͑typically Ͼ1 eV͒, 5d states do not show up in the photocurrent excitation spectrum. The fact that the absorption and photocurrent excitation spectra of LaAlO 3 :Ce 3+ are identical and that the photocurrent spectrum is temperature independent suggests that the lowest energy 5d state Ce 3+ is located inside the CB of LaAlO 3 .…”

Section: Resultsmentioning

confidence: 99%

Luminescence quenching by photoionization and electron transport in a LaAlO3:Ce3+ crystal

Kolk

Haas

Bos

et al. 2007

Journal of Applied Physics

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A combined photoconductivity, absorption, and thermoluminescence study was performed to understand the absence of luminescence from Ce 3+ in LaAlO 3 :Ce 3+ . It is demonstrated that the absence of luminescence is the result of Ce 3+ ionization from the 5d excited states, which are all located in the conduction band. Ce 3+ ionization is accompanied by the formation of several broad absorption and photoconductivity bands, which are assigned to electron traps. A time and temperature dependent optical investigation of these traps reveals the conditions under which electrons are transferred from Ce 3+ to traps and vice versa, from traps back to Ce 4+ . The observed difference in energy needed to thermally or optically release electrons from traps is qualitatively explained in terms of the location of the ground and excited states of the electron traps with respect to the conduction band.

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Section: Resultsmentioning

confidence: 99%

Luminescence quenching by photoionization and electron transport in a LaAlO3:Ce3+ crystal

Kolk

Haas

Bos

et al. 2007

Journal of Applied Physics

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“…Whereas the latter can be considered impurity levels, the delocalized nature of the 5f 1 7s 1 states indicates that they might be considered U 4+ trapped excitons, using the terminology proposed by McClure and Pedrini. 33 Furthermore, some members of the 5f n−1 6d͑e g ͒ 1 set seem to be notably influenced by the 5f 1 7s 1 states through a considerable interconfigurational mixing. All of this makes the electronic structure of the levels lying at high energies more complex than that of isomorphous and similar systems studied before ͑like Cs 2 ZrCl 6 :Pa 4+ , Cs 2 NaYCl 6 :U 3+ , and Cs 2 ZrCl 6 :U 4+ , from Refs.…”

Section: Resultsmentioning

confidence: 99%

The 5f2→5f16d1 absorption spectrum of Cs2GeF6:U4+ crystals: A quantum chemical and experimental study

Ordejón

Karbowiak

Seijo

et al. 2006

The Journal of Chemical Physics

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Single crystals of U 4+ -doped Cs 2 GeF 6 with 1% U 4+ concentration have been obtained by the modified Bridgman-Stockbarger method in spite of the large difference in ionic radii between Ge 4+ and U 4+ in octahedral coordination. Their UV absorption spectrum has been recorded at 7 K, between 190 and 350 nm; it consists of a first broad and intense band peaking at about 38 000 cm −1 followed by a number of broad bands of lower intensity from 39 000 to 45 000 cm −1 . None of the bands observed shows appreciable fine vibronic structure, so that the energies of experimental electronic origins cannot be deduced and the assignment of the experimental spectrum using empirical methods based on crystal field theory cannot be attempted. Alternatively, the profile of the absorption spectrum has been obtained theoretically using the U-F bond lengths and totally symmetric vibrational frequencies of the ground 5f 2 −1A 1g and 5f 1 6d͑t 2g ͒ 1 − iT 1u excited states, their energy differences, and their corresponding electric dipole transition moments calculated using the relativistic ab initio model potential embedded cluster method. The calculations suggest that the observed bands are associated with the lowest five 5f 2 −1A 1g → 5f 1 6d͑t 2g ͒ 1 − iT 1u ͑i =1-5͒ dipole allowed electronic origins and their vibrational progressions. In particular, the first broad and intense band peaking at about 38 000 cm −1 can be safely assigned to the 0-0 and 0-1 members of the a 1g progression of the 5f 2 −1A 1g → 5f 1 6d͑t 2g ͒ 1 −1T 1u electronic origin. The electronic structure of all the states with main configurational character 5f 1 6d͑t 2g ͒ 1 has been calculated as well. The results show that the lowest crystal level of this manifold is 5f 1 6d͑t 2g ͒ 1 −1E u and lies about 6200 cm −1 above the 5f 2 level closest in energy, which amounts to some 11 vibrational quanta. This large energy gap could result in low nonradiative decay and efficient UV emission, which suggest the interest of investigating further this new material as a potential UV solid state laser.

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“…A 21 and A 31 are the radiative rates from the ITE levels. exciton state (3) and radiatively decay to the ytterbium ground state (1). The second process is the IR pulse liberating electrons from trap states to the conduction band (C) where they recombine with ytterbium ions to form impurity-trapped excitons in the lower exciton state (2) which radiates to the ytterbium ground state (1).…”

Section: E Analysis Of Emission Dynamicsmentioning

confidence: 99%

“…ITEs are bound electron-hole pairs with the hole localized on an impurity (in this case the Yb 2+ ion) and the electron on nearby lattice sites. 1 The electron has been assumed to be localized on the neighboring cations 2 but recent ab initio studies of ITE states have shown that the exciton radius may be smaller. 3,4 Many materials have ITE states that play a role in relaxation processes but studying impurity-trapped excitons in optical materials is often difficult since the ITEs that form in these systems decay predominantly nonradiatively and so have to be studied indirectly.…”

Section: Introductionmentioning

confidence: 99%

Site-selective transient photoluminescence enhancement of impurity-trapped excitons in NaMgF3:Yb2+

et al. 2013

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The excited-state structure of impurity-trapped excitons are measured in a multisite system. We use a two-color (UV-IR) pulsed photoluminescence enhancement technique, which probes the interlevel transitions and dynamics of impurity-trapped excitons in doped insulating phosphor materials. The technique is applied to NaMgF 3 :Yb 2+ , which exhibits emission from two charge-compensation centers with peaks at 22300 cm −1 (448 nm) and 24000 cm −1 (417 nm). The observed photoluminescence enhancement is caused by a combination of intraexcitonic excitation and electron trap liberation. The electron traps are inferred to have a depth of approximately 800 cm −1 .

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Excitons trapped at impurity centers in highly ionic crystals

Cited by 164 publications

References 7 publications

Luminescence quenching by photoionization and electron transport in a LaAlO3:Ce3+ crystal

Luminescence quenching by photoionization and electron transport in a LaAlO3:Ce3+ crystal

The 5f2→5f16d1 absorption spectrum of Cs2GeF6:U4+ crystals: A quantum chemical and experimental study

Site-selective transient photoluminescence enhancement of impurity-trapped excitons in NaMgF3:Yb2+

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