TY  - JOUR
AU  - Racu, Andrei V.
AU  - Ristić, Zoran
AU  - Ćirić, Aleksandar
AU  - Ðorđević, Vesna
AU  - Buse, Gabriel
AU  - Poienar, Maria
AU  - Gutmann, Michael J.
AU  - Ivashko, Oleh
AU  - Stef, Marius
AU  - Vizman, Daniel
AU  - Dramićanin, Miroslav
AU  - Piasecki, Michal
AU  - Brik, Mikhail G.
PY  - 2023
UR  - https://vinar.vin.bg.ac.rs/handle/123456789/10561
AB  - The understanding of complex relationships between luminescent properties, local symmetry of an emitting center, and the host crystal structure provides a better insight into optical properties of materials. In this work, the alkaline earths CaF2 and BaF2 fluoride crystals doped with 0.1 mol% ErF3 were investigated. The crystals structure has been studied using a synchrotron and laboratory X-ray diffraction. The C3v and C4v sites symmetry were determined using erbium probed high resolution emission spectroscopy (HRPL) at low temperature (LT) of 10 K. The considerable difference in room temperature (RT) optical properties for CaF2 compared to BaF2 crystals was observed. Such difference in absorption intensity of 4.7 times of erbium 4G11/2 manifold in UV, and 7.5 times in green emission from 4S3/2 manifold, could be due to the distinction in the host crystals cationic radius (ΔrCa,Ba) and the dopant-host ionic radius (ΔrCa-Er, ΔrBa-Er). Those Δr differences influence the structure and lead to the following symmetry formation: In CaF2, the C4v and C3v isolated centers were identified, with the determined Er3+- F−i bond lengths of 2.734 Å and 4.735 Å respectively; In BaF2, only C3v isolated centers were identified with the determined Er3+- F−i bond lengths of 5.380 Å. The present work is the first study that takes into account correlations of optical properties, the local symmetry and the structure in mentioned fluorides crystals, and it could be a step forward in the lanthanide doped optical materials systematics.
T2  - Optical Materials
T1  - Analysis of site symmetries of Er3+ doped CaF2 and BaF2 crystals by high resolution photoluminescence spectroscopy
VL  - 136
SP  - 113337
DO  - 10.1016/j.optmat.2022.113337
ER  - 

@article{
author = "Racu, Andrei V. and Ristić, Zoran and Ćirić, Aleksandar and Ðorđević, Vesna and Buse, Gabriel and Poienar, Maria and Gutmann, Michael J. and Ivashko, Oleh and Stef, Marius and Vizman, Daniel and Dramićanin, Miroslav and Piasecki, Michal and Brik, Mikhail G.",
year = "2023",
abstract = "The understanding of complex relationships between luminescent properties, local symmetry of an emitting center, and the host crystal structure provides a better insight into optical properties of materials. In this work, the alkaline earths CaF2 and BaF2 fluoride crystals doped with 0.1 mol% ErF3 were investigated. The crystals structure has been studied using a synchrotron and laboratory X-ray diffraction. The C3v and C4v sites symmetry were determined using erbium probed high resolution emission spectroscopy (HRPL) at low temperature (LT) of 10 K. The considerable difference in room temperature (RT) optical properties for CaF2 compared to BaF2 crystals was observed. Such difference in absorption intensity of 4.7 times of erbium 4G11/2 manifold in UV, and 7.5 times in green emission from 4S3/2 manifold, could be due to the distinction in the host crystals cationic radius (ΔrCa,Ba) and the dopant-host ionic radius (ΔrCa-Er, ΔrBa-Er). Those Δr differences influence the structure and lead to the following symmetry formation: In CaF2, the C4v and C3v isolated centers were identified, with the determined Er3+- F−i bond lengths of 2.734 Å and 4.735 Å respectively; In BaF2, only C3v isolated centers were identified with the determined Er3+- F−i bond lengths of 5.380 Å. The present work is the first study that takes into account correlations of optical properties, the local symmetry and the structure in mentioned fluorides crystals, and it could be a step forward in the lanthanide doped optical materials systematics.",
journal = "Optical Materials",
title = "Analysis of site symmetries of Er3+ doped CaF2 and BaF2 crystals by high resolution photoluminescence spectroscopy",
volume = "136",
pages = "113337",
doi = "10.1016/j.optmat.2022.113337"
}

Racu, A. V., Ristić, Z., Ćirić, A., Ðorđević, V., Buse, G., Poienar, M., Gutmann, M. J., Ivashko, O., Stef, M., Vizman, D., Dramićanin, M., Piasecki, M.,& Brik, M. G.. (2023). Analysis of site symmetries of Er3+ doped CaF2 and BaF2 crystals by high resolution photoluminescence spectroscopy. in Optical Materials, 136, 113337.
https://doi.org/10.1016/j.optmat.2022.113337

Racu AV, Ristić Z, Ćirić A, Ðorđević V, Buse G, Poienar M, Gutmann MJ, Ivashko O, Stef M, Vizman D, Dramićanin M, Piasecki M, Brik MG. Analysis of site symmetries of Er3+ doped CaF2 and BaF2 crystals by high resolution photoluminescence spectroscopy. in Optical Materials. 2023;136:113337.
doi:10.1016/j.optmat.2022.113337 .

Racu, Andrei V., Ristić, Zoran, Ćirić, Aleksandar, Ðorđević, Vesna, Buse, Gabriel, Poienar, Maria, Gutmann, Michael J., Ivashko, Oleh, Stef, Marius, Vizman, Daniel, Dramićanin, Miroslav, Piasecki, Michal, Brik, Mikhail G., "Analysis of site symmetries of Er3+ doped CaF2 and BaF2 crystals by high resolution photoluminescence spectroscopy" in Optical Materials, 136 (2023):113337,
https://doi.org/10.1016/j.optmat.2022.113337 . .

TY  - JOUR
AU  - Mironova-Ulmane, Nina
AU  - Brik, Mikhail G.
AU  - Grube, Jurgis
AU  - Krieke, Guna
AU  - Kemere, Meldra
AU  - Antuzevics, Andris
AU  - Gabrusenoks, E.
AU  - Skvortsova, Vera N.
AU  - Elsts, Edgars
AU  - Sarakovskis, Anatolijs
AU  - Piasecki, Michal
AU  - Popov, Anatoli I.
PY  - 2022
UR  - https://vinar.vin.bg.ac.rs/handle/123456789/10397
AB  - The optical spectra of a single crystal of α-Al2O3Cr3+ were studied in a wide temperature range. The crystal was demonstrated to have a potential for optical thermometric applications. Three ways of measuring temperature were tested and analyzed: i) luminescence intensity ratio of the R1 and R2 lines; ii) change of the full width of half maxima of the R1 and R2 lines, and iii) thermal shifts of the R1 and R2 lines maxima. The highest absolute and relative sensitivities were obtained at cryogenic temperatures. In addition, the thermal shifts of the R lines were analyzed using the McCumber-Sturge equation to estimate the Debye temperature and the electron-vibrational interaction parameter.
T2  - Optical Materials
T1  - EPR, optical and thermometric studies of Cr3+ ions in the α-Al2O3 synthetic single crystal
VL  - 132
SP  - 112859
DO  - 10.1016/j.optmat.2022.112859
ER  - 

@article{
author = "Mironova-Ulmane, Nina and Brik, Mikhail G. and Grube, Jurgis and Krieke, Guna and Kemere, Meldra and Antuzevics, Andris and Gabrusenoks, E. and Skvortsova, Vera N. and Elsts, Edgars and Sarakovskis, Anatolijs and Piasecki, Michal and Popov, Anatoli I.",
year = "2022",
abstract = "The optical spectra of a single crystal of α-Al2O3Cr3+ were studied in a wide temperature range. The crystal was demonstrated to have a potential for optical thermometric applications. Three ways of measuring temperature were tested and analyzed: i) luminescence intensity ratio of the R1 and R2 lines; ii) change of the full width of half maxima of the R1 and R2 lines, and iii) thermal shifts of the R1 and R2 lines maxima. The highest absolute and relative sensitivities were obtained at cryogenic temperatures. In addition, the thermal shifts of the R lines were analyzed using the McCumber-Sturge equation to estimate the Debye temperature and the electron-vibrational interaction parameter.",
journal = "Optical Materials",
title = "EPR, optical and thermometric studies of Cr3+ ions in the α-Al2O3 synthetic single crystal",
volume = "132",
pages = "112859",
doi = "10.1016/j.optmat.2022.112859"
}

Mironova-Ulmane, N., Brik, M. G., Grube, J., Krieke, G., Kemere, M., Antuzevics, A., Gabrusenoks, E., Skvortsova, V. N., Elsts, E., Sarakovskis, A., Piasecki, M.,& Popov, A. I.. (2022). EPR, optical and thermometric studies of Cr3+ ions in the α-Al2O3 synthetic single crystal. in Optical Materials, 132, 112859.
https://doi.org/10.1016/j.optmat.2022.112859

Mironova-Ulmane N, Brik MG, Grube J, Krieke G, Kemere M, Antuzevics A, Gabrusenoks E, Skvortsova VN, Elsts E, Sarakovskis A, Piasecki M, Popov AI. EPR, optical and thermometric studies of Cr3+ ions in the α-Al2O3 synthetic single crystal. in Optical Materials. 2022;132:112859.
doi:10.1016/j.optmat.2022.112859 .

Mironova-Ulmane, Nina, Brik, Mikhail G., Grube, Jurgis, Krieke, Guna, Kemere, Meldra, Antuzevics, Andris, Gabrusenoks, E., Skvortsova, Vera N., Elsts, Edgars, Sarakovskis, Anatolijs, Piasecki, Michal, Popov, Anatoli I., "EPR, optical and thermometric studies of Cr3+ ions in the α-Al2O3 synthetic single crystal" in Optical Materials, 132 (2022):112859,
https://doi.org/10.1016/j.optmat.2022.112859 . .

TY  - JOUR
AU  - Andreici Etimie, E. L.
AU  - Avram, Nicolae M.
AU  - Brik, Mikhail G.
PY  - 2022
UR  - https://vinar.vin.bg.ac.rs/handle/123456789/10452
AB  - The normal spinels (Mg, Zn)Al2O4 doped with transition metal (TM) ions Cr3+/Co2+ are versatile materials with important electronic, optical and spectral properties. In addition to being used in many applications, they are excellent systems for testing some models and simulation features. The aim of this paper is to present, in the unified frame, the results on d-d transitions and ligand field parameters (LFPs) for the title systems, based on ab initio calculations, combining periodic density functional theory (DFT) supercell approach with ab initio (AI) multi -reference perturbation theory (MRPT) and multi-reference configuration interaction (MRCI) methods. These AI methods, based on complete active space self-consistent-field (CASSCF) reference, allow to calculate and investigate the energy levels of TM ions and the d-d transitions between them. From the AI results the B and C Racah parameters, the spin-orbit coupling (SOC) constant and the LFPs in the frame of the angular overlap model (AOM) were accurately extracted with ab initio ligand field theory (AILFT) protocol, all with subsequent comparison with the experimental data or existing theoretical results in the literature. The calculation technique presented in this paper serves as a predictive formalism for further studies of larger monomer clusters, for which experimental data is unreliable or unavailable.
T2  - Optical Materials: X
T1  - The d-d transitions and ligand field parameters for Cr3+/Co2+ doped (Mg, Zn)Al2O4: Multi-reference Ab initio investigations
VL  - 16
SP  - 100188
DO  - 10.1016/j.omx.2022.100188
ER  - 

@article{
author = "Andreici Etimie, E. L. and Avram, Nicolae M. and Brik, Mikhail G.",
year = "2022",
abstract = "The normal spinels (Mg, Zn)Al2O4 doped with transition metal (TM) ions Cr3+/Co2+ are versatile materials with important electronic, optical and spectral properties. In addition to being used in many applications, they are excellent systems for testing some models and simulation features. The aim of this paper is to present, in the unified frame, the results on d-d transitions and ligand field parameters (LFPs) for the title systems, based on ab initio calculations, combining periodic density functional theory (DFT) supercell approach with ab initio (AI) multi -reference perturbation theory (MRPT) and multi-reference configuration interaction (MRCI) methods. These AI methods, based on complete active space self-consistent-field (CASSCF) reference, allow to calculate and investigate the energy levels of TM ions and the d-d transitions between them. From the AI results the B and C Racah parameters, the spin-orbit coupling (SOC) constant and the LFPs in the frame of the angular overlap model (AOM) were accurately extracted with ab initio ligand field theory (AILFT) protocol, all with subsequent comparison with the experimental data or existing theoretical results in the literature. The calculation technique presented in this paper serves as a predictive formalism for further studies of larger monomer clusters, for which experimental data is unreliable or unavailable.",
journal = "Optical Materials: X",
title = "The d-d transitions and ligand field parameters for Cr3+/Co2+ doped (Mg, Zn)Al2O4: Multi-reference Ab initio investigations",
volume = "16",
pages = "100188",
doi = "10.1016/j.omx.2022.100188"
}

Andreici Etimie, E. L., Avram, N. M.,& Brik, M. G.. (2022). The d-d transitions and ligand field parameters for Cr3+/Co2+ doped (Mg, Zn)Al2O4: Multi-reference Ab initio investigations. in Optical Materials: X, 16, 100188.
https://doi.org/10.1016/j.omx.2022.100188

Andreici Etimie EL, Avram NM, Brik MG. The d-d transitions and ligand field parameters for Cr3+/Co2+ doped (Mg, Zn)Al2O4: Multi-reference Ab initio investigations. in Optical Materials: X. 2022;16:100188.
doi:10.1016/j.omx.2022.100188 .

Andreici Etimie, E. L., Avram, Nicolae M., Brik, Mikhail G., "The d-d transitions and ligand field parameters for Cr3+/Co2+ doped (Mg, Zn)Al2O4: Multi-reference Ab initio investigations" in Optical Materials: X, 16 (2022):100188,
https://doi.org/10.1016/j.omx.2022.100188 . .

TY  - JOUR
AU  - Srivastava, Alok M.
AU  - Brik, Mikhail G.
AU  - Beers, William W.
AU  - Cohen, William E.
PY  - 2022
UR  - https://vinar.vin.bg.ac.rs/handle/123456789/10601
AB  - The relationship between the Stokes shift of Bi3+ emission and the volume of the unit-cell in two series of orthorhombic perovskites, LnB 3+O3 (Ln = La, Gd, Y; B 3+ = Al, In, Ga) and AB 4+O3 (A = Ca, Sr; B 4+ = Zr, Sn) is explored. The Stokes shift increases linearly with increasing cell volume. This is explained qualitatively by the lattice chemical pressure acting on the Bi3+ ion. The degree of Bi3+ ion off-centering displacement, which is due to the stereochemical activity of the lone-pair electrons (6 s2), is controlled by the chemical pressure. A small cell suppresses the off-centering displacement to produce a small Stokes shift of emission by limiting the excited state structural distortion. In large cell, the off-centering displacement is more easily accommodated. The elimination of ground state distortion in the excited state gives larger Stokes shift of emission. These qualitative arguments are supplemented by recent first-principles calculations on Bi3+ luminescence in these perovskites. The Bi3+ luminescence in SrZrO3, previously assigned to emission from the D-state, is now assigned to the localized 3P0,1 → 1S0 transition. The energy of the 1S0 → 3P1 transition is correlated with the covalence of the BO6/2 perovskite framework. Discussion on the effective ionic radius of the Bi3+ ion in these perovskites is presented.
T2  - ECS Journal of Solid State Science and Technology
T1  - Chemical Pressure Effects on the Stokes Shift of Bi3+ Luminescence in Orthorhombic Perovskites
VL  - 11
IS  - 9
SP  - 096003
DO  - 10.1149/2162-8777/ac915b
ER  - 

@article{
author = "Srivastava, Alok M. and Brik, Mikhail G. and Beers, William W. and Cohen, William E.",
year = "2022",
abstract = "The relationship between the Stokes shift of Bi3+ emission and the volume of the unit-cell in two series of orthorhombic perovskites, LnB 3+O3 (Ln = La, Gd, Y; B 3+ = Al, In, Ga) and AB 4+O3 (A = Ca, Sr; B 4+ = Zr, Sn) is explored. The Stokes shift increases linearly with increasing cell volume. This is explained qualitatively by the lattice chemical pressure acting on the Bi3+ ion. The degree of Bi3+ ion off-centering displacement, which is due to the stereochemical activity of the lone-pair electrons (6 s2), is controlled by the chemical pressure. A small cell suppresses the off-centering displacement to produce a small Stokes shift of emission by limiting the excited state structural distortion. In large cell, the off-centering displacement is more easily accommodated. The elimination of ground state distortion in the excited state gives larger Stokes shift of emission. These qualitative arguments are supplemented by recent first-principles calculations on Bi3+ luminescence in these perovskites. The Bi3+ luminescence in SrZrO3, previously assigned to emission from the D-state, is now assigned to the localized 3P0,1 → 1S0 transition. The energy of the 1S0 → 3P1 transition is correlated with the covalence of the BO6/2 perovskite framework. Discussion on the effective ionic radius of the Bi3+ ion in these perovskites is presented.",
journal = "ECS Journal of Solid State Science and Technology",
title = "Chemical Pressure Effects on the Stokes Shift of Bi3+ Luminescence in Orthorhombic Perovskites",
volume = "11",
number = "9",
pages = "096003",
doi = "10.1149/2162-8777/ac915b"
}

Srivastava, A. M., Brik, M. G., Beers, W. W.,& Cohen, W. E.. (2022). Chemical Pressure Effects on the Stokes Shift of Bi3+ Luminescence in Orthorhombic Perovskites. in ECS Journal of Solid State Science and Technology, 11(9), 096003.
https://doi.org/10.1149/2162-8777/ac915b

Srivastava AM, Brik MG, Beers WW, Cohen WE. Chemical Pressure Effects on the Stokes Shift of Bi3+ Luminescence in Orthorhombic Perovskites. in ECS Journal of Solid State Science and Technology. 2022;11(9):096003.
doi:10.1149/2162-8777/ac915b .

Srivastava, Alok M., Brik, Mikhail G., Beers, William W., Cohen, William E., "Chemical Pressure Effects on the Stokes Shift of Bi3+ Luminescence in Orthorhombic Perovskites" in ECS Journal of Solid State Science and Technology, 11, no. 9 (2022):096003,
https://doi.org/10.1149/2162-8777/ac915b . .