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1.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Orlov Yu. S., Nikolaev S. V., Dudnikov V. A., Gavrichkov V. A., Ovchinnikov S. G.
Заглавие : Features of spin crossovers in magnetic materials
Колич.характеристики :26 с
Место публикации : Phys. Usp. - 2023. - Vol. 66, Is. 7. - P.647-672. - ISSN 10637869 (ISSN), DOI 10.3367/UFNe.2022.05.039195. - ISSN 14684780 (eISSN)
Примечания : Cited References: 237. - The authors thank the Russian Science Foundation for financial support in the framework of project no. 18-12-00022
Аннотация: We present experimental and theoetical results of spin crossover studies in magnetically ordered materials. The effect of spin crossovers on the electronic structure of transition metal oxides and on the Bose condensation of spin excitons in the vicinity of the spin crossover is considered. A new method for calculating the interatomic superexchange interaction in transition metal oxides is discussed that allows considering selective contributions of excited magnetic cation terms. Changes in the exchange interaction sign are predicted for spin crossovers for d5—d7 ions. In the RCoO3 family of rare-earth cobaltites, the ground state is nonmagnetic, but, as the temperature increases, thermal excitations of high-spin states give rise to a number of experimentally detectable features. In defective RCoO3 samples, stabilization of the high-spin term and ferromagnetic ordering are possible. Dynamical crossovers under external pumping and the dynamics of multiplicity, magnetization, and local lattice distortions are discussed. Geophysical implications of spin crossovers are considered, and metallic properties of Earth's mantle at a depth of 1400—1800 km are predicted.
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2.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Orlov Yu. S., Nikolaev S. V., Dudnikov V. A., Ovchinnikov S. G.
Заглавие : Forming a dielectric exciton phase in strongly correlated systems with spin crossover
Место публикации : Phys. Rev. B. - 2021. - Vol. 104, Is. 19. - Ст.195103. - ISSN 24699950 (ISSN), DOI 10.1103/PhysRevB.104.195103
Примечания : Cited References: 46. - The authors thank the Russian Scientific Foundation for financial support under Grant No. 18-12-00022
Аннотация: Formation of the magnetic structure and exciton condensate of local magnetic excitons in strongly correlated systems near the spin crossover under high pressure is considered in terms of the effective Hamiltonian obtained from a two-band Hubbard model in the regime of strong electron correlations. The coexistence of the long-range antiferromagnetic order and exciton condensate and the occurrence of the magnetization caused by the condensation of local magnetic excitons are demonstrated. Transformation of the electronic structure of the antiferromagnetic high-spin insulator into the paramagnetic two-band correlated metal via a narrow-gap antiferromagnetic excitonic semiconductor is obtained.
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3.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Li, Mingze, Li, Yawen, Molokeev M. S., Zhao, Jing, Na, Guangren, Zhang, Lijun, Xia, Zhiguo
Заглавие : Halogen substitution in zero-dimensional mixed metal halides toward photoluminescence modulation and enhanced quantum yield
Место публикации : Adv. Opt. Mater. - 2020. - Vol. 8, Is. 16. - Ст.2000418. - ISSN 2195-1071, DOI 10.1002/adom.202000418
Примечания : Cited References: 34. - M.L., Y.L. contributed equaly to this work. This work was supported by the National Natural Science Foundation of China (51961145101, 51972118, and 51722202), Fundamental Research Funds for the Central Universities (FRFTP-18-002C1), the Guangdong Provincial Science &Technology Project (2018A050506004), and the Local Innovative and Research Teams Project of Guangdong Pearl River Talents Program (2017BT01 x 137). This work was also funded by RFBR according to the research project No. 19-52-80003. The work at Jilin University is supported by the National Natural Science Foundation of China (Grant No. 61722403 and 11674121) and Jilin Province Science and Technology Development Program (Grant No. 20190201016JC). Calculations were performed in part at the high performance computing center of Jilin University.
Предметные рубрики: WHITE-LIGHT EMISSION
PEROVSKITES
EXCITONS
Аннотация: Zero‐dimensional (0D) organic−inorganic hybrid metal halides haveunprecedented degrees of freedom for structural tunability and photoluminescence modulation. Here, the 0D isomorphic hybrid metal mixed halides (C9NH20)9Pb3Zn2Br19(1−x )Cl19x (x = 0–1) with continuous halogen contents control, exhibiting tunable emission and enhancement of photoluminescence quantum yield (PLQY) are reported. The competitive bromine to chlorine substitution process in (C9NH20)9Pb3Zn2Br19(1−x )Cl19x occurs first in [ZnBr4−x Clx ]2− tetrahedron before the [Pb3Br11−x Clx ]5− trimer. The increasing Cl content in samples from x = 0 to 1 results in an expected blue shift of emission peak from 565 to 516 nm, and meanwhile a strikingly room temperature PL quantum yield increase from 8% to 91%. Combined experimental characterizations and theoretical calculations indicate that the blue shift of interband transition energy is responsible for the emission peak shift. Moreover, with the increasing Cl content, the enhanced electron−phonon interaction and the weakened thermal‐assisted nonradiative recombination result in more efficient radiative transition channels and ultimately enhanced PLQY. The impact of halogen substitution on electronic structures and optical properties in 0D hybrid metal halides is emphasized in this work as a new strategy to promote the future development of new luminescent materials.
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4.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Ovchinnikov S. G.
Заглавие : Spin excitons - A new mechanism of superconducting pairing in copper oxides
Место публикации : JETP Letters. - 1996. - Vol. 64, Is. 1. - P.25-31. - ISSN 0021-3640, DOI 10.1134/1.567153
Примечания : Cited References: 22
Предметные рубрики: HIGH-TC SUPERCONDUCTORS
SINGLET-TRIPLET MODEL
LA2-XSRXCUO4
SR2CUO2CL2
PLANE
Аннотация: The Fermi and Bose quasiparticle spectrum in copper oxides is studied in a many-band p-d model taking account of the strong electronic correlations. It is shown that hole-doped systems possess a Bose mode - a spin exciton - which is associated with the singlet-triplet excitation of the two-hole ground-state term of CuO4 clusters. Intercluster hopping leads to fermion-boson interaction with a spin exciton as the intermediate boson. Such a mechanism does not exist for n-type systems. (C) 1996 American Institute of Physics.
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5.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Ovchinnikov S. G., Zabluda V. N.
Заглавие : The energy band structure and optical spectra of FeBO3 calculated with allowance for strong electron correlations
Место публикации : J. Exp. Theor. Phys.: AMER INST PHYSICS, 2004. - Vol. 98, Is. 1. - P135-143. - ISSN 1063-7761, DOI 10.1134/1.1648107
Примечания : Cited References: 32. - This study was supported by the Russian Foundation for Basic Research (project no. 03-02-16286) and by the “Strongly Correlated Electrons” Program of the Department of Physical Sciences of the Russian Academy of Sciences
Предметные рубрики: PHASE-TRANSITION
HIGH-PRESSURE
FERROMAGNETISM
MODEL
Ключевые слова (''Своб.индексиров.''): atomic physics--band structure--charge transfer--excitons--green's function--light absorption--dielectric gap--energy band structure--lehmann spectral representation--optical spectra--iron compounds
Аннотация: A model of the energy band structure of iron borate (FeBO3) is proposed that combines a one-electron description of the sp states of boron and oxygen with a many-electron description of the d states of iron. The Green functions of d electrons are calculated using the exact Lehmann spectral representation. The energies of the d-type quasiparticles are calculated using terms of the d(4) , d(5) , and d(6) electron configurations. The optical absorption spectrum of FeBO3 is determined by local excitons and by the electron excitations with charge transfer. The latter excitations control the nature of the dielectric gap in FeBO3 crystals. The model parameters are determined from a comparison to the exciton energies. The density of single-particle states in FeBO3 is calculated. The main bands in the calculated optical absorption spectrum agree well with experimental data for energies up to 3 eV. (C) 2004 MAIK "Nauka/Interperiodica".
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6.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Pustovarov V. A., Ogorodnikov I. N., Omelkov S. I., Molokeev M. S., Kozlov A. V., Isaenko L. I.
Заглавие : Photoluminescence of monoclinic Li3AlF6 crystals under vacuum ultraviolet and soft X-ray excitations
Место публикации : Opt. Mater.: Elsevier, 2015. - Vol. 49. - P.201-207. - ISSN 0925-3467, DOI 10.1016/j.optmat.2015.09.011
Примечания : Cited References: 49. - This work was partly supported by the Ministry of Education and Science of the Russian Federation (the basic part of the government mandate); Center of Excellence "Radiation and Nuclear Technologies" (Competitiveness Enhancement Program of Ural Federal University, Russia), HASYLAB DESY (Projects Nos. 20110843, 20080119EC), European Social Fund ("Mobilitas" program, MJD219), Estonian Research Council (Institutional Research Funding IUT02-26) and Baltic Science Link project coordinated by the Swedish Research Council, VR
Предметные рубрики: LiBaAlF6 single-crystals
F-type centers
LiBaF3 crystals
Color-centers
Recombination luminescence
Rietveld refinement
VUV spectroscopy
Trapped excitons
Energy-transfer
Pure
Ключевые слова (''Своб.индексиров.''): li3alf6--time-resolved luminescence--vuv spectroscopy--defects
Аннотация: Using Bridgman technique we have grown monoclinic β-LiAF crystals suitable for optical studies, performed XRD-identification and Rietveld refinement of the crystal structure and carried out a photoluminescence study upon vacuum ultraviolet (VUV) and extreme ultraviolet (XUV)-excitations, using the low-temperature (T = 7.2 K) time-resolved VUV-spectroscopy technique. The intrinsic PL emission band at 340–350 nm has been identified as due to radiative recombination of self-trapped excitons. The electronic structure parameters were determined: bandgap E g ≈ 12.5 eV, energy threshold for creation of unrelaxed excitons 11.8 eV < E n < 12.5 eV . The PL emission bands at 320–325 and 450 nm were attributed to luminescence caused by lattice defects. We have discovered an efficient excitation of PL emission bands in the energy range of interband transitions ( E ex > 13.5 eV), as well as in the energy range of core transitions at 130 eV. We have revealed UV–VUV PL emission bands at 170 and 208 nm due to defects. A reasonable assumptions about the origin of the UV–VUV bands were discussed.
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7.

Вид документа : Статья из сборника (однотомник)
Шифр издания :
Автор(ы) : Boldyrev K. N., Popova M. N., Bezmaternykh L. N., Pisarev R. V.
Заглавие : Pronounced coupling of 3D-excitons with magnetic phase transitions in CuB2O4
Коллективы : Moscow International Symposium on Magnetism, Московский государственный университет им. М.В. Ломоносова
Место публикации : Moscow int. Symp. on Magnet. (MISM-2014): Book of abstracts. - 2014. - Ст.2OR-H-4. - P.697. - ISBN 978-5-91978-025-0
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8.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Jing Y., Liu Y., Jiang X., Molokeev M. S., Lin Z., Xia Z.
Заглавие : Sb3+dopant and halogen substitution triggered highly efficient and tunable emission in lead-free metal halide single crystals
Место публикации : Chem. Mater. - 2020. - Vol. 32, Is. 12. - P.5327-5334. - ISSN 08974756 (ISSN), DOI 10.1021/acs.chemmater.0c01708
Примечания : Cited References: 46. - This work is supported by the National Natural Science Foundation of China (51961145101, 51972118, and 51722202), Fundamental Research Funds for the Central Universities (FRFTP-18-002C1), Guangzhou Science & Technology Project (202007020005), Guangdong Provincial Science &Technology Project (2018A050506004), and the Local Innovative and Research Teams Project of Guangdong Pearl River Talents Program (2017BT01X137). This work is also funded by RFBR according to the research project no. 19-52-80003
Аннотация: Rational doping and compositional control remain significant challenges in designing luminescent metal halides to achieve highly efficient and tunable emission. Here, the air-stable lead-free Cs2InCl5·H2O crystal with a zero-dimensional structure was investigated as a pristine compound to design new luminescence materials. Sb3+-doping in Cs2InCl5·H2O:Sb3+ enabled broadband yellow emission with a photoluminescence quantum yield up to 95.5%. The emission colors can be expanded into the orange-red region by halogen compositional substitution for Cs2InX5·H2O:Sb3+ (X = Cl/Br/I). The optical characterizations along with the theoretical calculations demonstrate that the characteristic singlet and triplet self-trapped exciton emissions of ns2-metal-halide centers account for the tunable luminescence. Moreover, the admirable stability against air and heat pave way for its further applications in white light-emitting diodes and high-resolution fluorescent signs in anticounterfeiting technology. Our achievement in the case of Sb3+-doped Cs2InCl5·H2O represents a successful strategy for developing stable lead-free metal halides with highly efficient emission for versatile optical applications.
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9.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Isaenko L. I., Yelisseyev A. P., Lobanov S. I., Krinitsin P. G., Molokeev M. S.
Заглавие : Structure and optical properties of Li2Ga2GeS6 nonlinear crystal
Коллективы : Russian Foundation of Basic Research [15-02-03408a]
Место публикации : Opt. Mater.: Elsevier Science, 2015. - Vol. 47. - P.413-419. - ISSN 0925-3467, DOI 10.1016/j.optmat.2015.06.014
Примечания : Cited References:23. - This work was supported by the Russian Foundation of Basic Research (Grant No. 15-02-03408a)
Предметные рубрики: PHASE-MATCHING PROPERTIES
MID-IR
PARAMETRIC AMPLIFICATION
GENERATION
LiGaS2
GROWTH
DAMAGE
Ga
Te
Se
Ключевые слова (''Своб.индексиров.''): li2ga2ges6--structure--absorption--raman--luminescence--excitons
Аннотация: Structure and optical properties of new nonlinear crystal - Li2Ga2GeS6 single crystal of optical quality, grown by the Bridgman technique were studied. The data on transmission, Raman scattering, luminescence emission, excitation and thermal quenching as well as thermostimulated luminescence are presented. Fundamental absorption edge is determined by the direct allowed electronic transitions: The values of optical band gap are estimated. Absorption band at 8.0 mu m is due to S-S vibrations. Features in photoluminescence spectra are associated with excitons: both free (narrow line at 371 nm) and self-trapped ones (broad bands at 596, 730 and 906 nm). Spontaneous emission in the 80-170 K range, both at crystal heating and cooling, is typical of pyroelectrics: This confirms the absence of symmetry center in Li2Ga2GeS6 and an opportunity of laser frequency nonlinear conversion. (C) 2015 Elsevier B.V. All rights reserved.
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10.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Zhou G., Wang Y., Mao Y., Guo C., Zhang J., Molokeev M. S., Xia Z., Zhang X.-M.
Заглавие : Temperature/component-dependent luminescence in lead-free hybrid metal halides for temperature sensor and anti-counterfeiting
Колич.характеристики :9 с
Место публикации : Adv. Funct. Mater. - 2024. - Ст.2401860. - Article in press. - ISSN 1616301X (ISSN), DOI 10.1002/adfm.202401860. - ISSN 16163028 (eISSN)
Примечания : Cited References: 89. - G.J.Z. and Y.T.W. contributed equally to this work. This work was supported by the National Natural Science Foundation of China (No.52202177, 22271211), Fundamental Research Program of Shanxi Province (No.20210302124054), Science and Technology Innovation Project of Colleges and Universities in Shanxi Province (No.2021L262), 1331 Project of Shanxi Province, Postgraduate Innovation Project of Shanxi Province (No.2023KY462), and supported by the Ministry of Science and High Education of Russian Federation (No.FSRZ-2023-0006). The authors would like to thank Prof. Haijun Jiao, Leibniz-Institut für Katalyse e.V., Germany, for the theoretical support on the electron-transition mechanism
Аннотация: Hybrid metal halides (HMHs) have emerged as a promising platform for optically functional crystalline materials, but it is extremely challenging to thoroughly elucidate the electron transition coupled to additional ligand emission. Herein, to discover sequences of lead-free HMHs with distinct optically active metal cations are aimed, that is, Sb3+ (5s2) with the lone-pair electron configuration and In3+ (4d10) with the fully-filled electron configuration. (Me2NH2)4MCl6·Cl (Me = −CH3, M = Sb, In) exhibits the superior temperature/component-dependent luminescence behaviors resulting from the competition transition between triplet-states (Tn-S0) self-trapped excitons (STEs) of inorganic units and singlet-state (S1-S0) of organic cations, which is manipulated by the optical activity levels of [SbCl6]3− and [InCl6]3−. The bonding differences between Sb3+/In3+ and Cl− in terms of electronic excitation and hybridization are emphasized, and the different electron-transition mechanisms are established according to the PL spectra at the extreme temperature of 5 to 305 K and theoretical calculations. By fine-tuning the B-site Sb3+/In3+ alloying, the photoluminescence quantum yield (PLQY = 81.5%) and stability are optimized at 20% alloying of Sb3+. This research sheds light on the rules governing PL behaviors of HMHs, as well as exploring the optical-functional application of aviation temperature sensors and access-control systems.
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