Critical points in photoluminescence spectra and their relation with phase transition in Nb-doped SrTiO 3
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Critical points in photoluminescence spectra and their relation with phase transition in Nb‑doped SrTiO3 Vadim Sh. Yalishev1 · Rashid A. Ganeev1,2 · Ali S. Alnaser1 · Shavkat U. Yuldashev3,4 Received: 7 April 2020 / Accepted: 20 May 2020 © Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract Luminescence spectra are extremely sensitive to variations in structural environment; thus, result of structural change, such as phase transition, can be observed via luminescence intensity. The temperature dynamic of photoluminescence in the Nb-doped SrTiO3 demonstrates two critical points at 115 and 160 K, which correspond to temperatures of structural phase transitions for the bulk and the surface of SrTiO3, respectively. The absence of a hysteresis effect in the photoluminescence emission points out the correspondence of the critical points to a second-order phase transition. Similar critical behaviours were also observed in oxygen-deficient SrTiO3, confirming a relationship between the PL and phase transition. The existence of peaks in the temperature coefficient of resistivity at the same temperatures also confirms the correlation between photoluminescence and phase transition in the Nb-doped S rTiO3, providing a simple non-contact method to detect phase transitions in luminescence materials. Keywords SrTiO3 single crystal · Temperature-activated photoluminescence · Phase transition
1 1. Introduction Perovskite-structured SrTiO3 (STO) has been the subject of a large variety of investigations because of its intriguing physical properties such as superconductivity [1], twodimensional electron gas [2], ferroelectricity [3] and luminescence [4], which arise after doping with a small number of electrons, indicating varied interaction of charge, spin, orbital and lattice degree of freedom. This oxide is known to undergo a second-order phase transition (PT) at temperature ~ 110 K from cubic to tetragonal structure with slightly rotated oxygen atoms around the z-axis. Some interesting properties in STO are believed to be related to this PT [5]. Pure STO is a wide-gap semiconductor with band gap * Vadim Sh. Yalishev [email protected] 1
Department of Physics, American University of Sharjah, PO Box 26666, Sharjah, UAE
2
Faculty of Physics, Voronezh State University, Voronezh, Russia 394006
3
Nano‑Information Technology Academy (NITA), Dongguk University, Seoul 100‑715, Korea
4
Department of Physics, National University of Uzbekistan, Tashkent, Uzbekistan 100174
energy of ~ 3.26 eV. Electron doping realized by O vacancies, La or Nb dopants transforms insulating STO into a metallic state even with small doping levels [4, 6]. The DC resistivity in n-doped STO demonstrated T2 temperature dependence below 100 K, which was described as results of phonon-mediated interactions [7–10]. In addition, the electron doping of STO was found to cause an emergence of ultraviolet near-band-edge (NBE) and blue photoluminescence (PL) emission [4, 11], which only were observed in pure STO u
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