Effects of calcination temperature and Li+ ions doping on structure and upconversion luminescence properties of TiO2:Ho3+-Yb3+ nanocrystals

Zou, Kaishun; Dong, Guang-Zong; Liu, Juncheng; Xu, Boxu; Wang, Danping

doi:10.1016/j.jmst.2018.10.018

Cited by 20 publications

(6 citation statements)

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“…ART of TiO 2 at high temperature could be controlled by the addition of metal ions, suitable chemical modifiers and an appropriate synthesis method [13]. Doping with metal ions is a one of the profitable ways to retard the ART [14,21,[23][24][25][26][27][28][29][30][31]. Metal ions could improve the thermal stability of TiO 2 through the reduction in contact points, and nucleation sites [32].Generally, doping of an element with higher oxidation state compared to Ti 4+ would improve charge carrier separation on the photocatalyst surface [33].…”

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confidence: 99%

Mo doped TiO₂: impact on oxygen vacancies, anatase phase stability and photocatalytic activity

et al. 2020

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This work outlines an experimental and theoretical investigation of the effect of molybdenum (Mo) doping on the oxygen vacancy formation and photocatalytic activity of TiO 2 . Analytical techniques such as x-ray diffraction (XRD), Raman, x-ray photoelectron spectroscopy (XPS) and photoluminescence (PL) were used to probe the anatase to rutile transition (ART), surface features and optical characteristics of Mo doped TiO 2 (Mo-TiO 2 ). XRD results showed that the ART was effectively impeded by 2 mol% Mo doping up to 750°C, producing 67% anatase and 33% rutile. Moreover, the crystal growth of TiO 2 was affected by Mo doping via its interaction with oxygen vacancies and the Ti-O bond. The formation of Ti-O-Mo and Mo-Ti-O bonds were confirmed by XPS results. Phonon confinement, lattice strain and non-stoichiometric defects were validated through the Raman analysis. DFT results showed that, after substitutional doping of Mo at a Ti site in anatase, the Mo oxidation state is Mo 6+ and empty Mo-s states emerge at the titania conduction band minimum. The empty Mo-d states overlap the anatase conduction band in the DOS plot. A large energy cost, comparable to that computed for pristine anatase, is required to reduce Mo-TiO 2 through oxygen vacancy formation. Mo 5+ and Ti 3+ are present after the oxygen vacancy formation and occupied states due to these reduced cations emerge in the energy gap of the titania host. PL studies revealed that the electron-hole recombination process in Mo-TiO 2 was exceptionally lower than that of TiO 2 anatase and rutile. This was ascribed to introduction of 5s gap states below the CB of TiO 2 by the Mo dopant. Moreover, the photo-generated charge carriers could easily be trapped and localised on the TiO 2 surface by Mo 6+ and Mo 5+ ions to improve the photocatalytic activity. coatings [8,9]. The most commonly existing crystalline polymorphs of TiO 2 are anatase, rutile and brookite [10][11][12]. Anatase is accepted to be the more active phase of TiO 2 and is preferred by the ceramic industries to fabricate light active antimicrobial indoor building materials such as ceramics, glass, tiles and sanitary surfaces [13,14]. This requires thermal stability of the anatase phase under typical ceramic processing conditions. TiO 2 anatase is mainly fabricated at low calcination temperatures (∼500°C) to prevent the anatase to rutile phase transition (ART) [15][16][17], which produces the less photo-active rutile phase. The photo-activity of anatase arises from its appropriate band edge positions, electron affinity, ionisation potential, and the long lifetime of charge carriers [10,12,18]. Moreover, transient photo-conductance analysis has revealed that the electron-hole recombination phenomena in anatase (101) phase is much slower compared to rutile (110), which is credited in part to the indirect band gap of anatase [11,19].The unit cells of anatase and rutile phases are composed of TiO 6 octahedra with titanium atoms at the centre and oxygen atoms at the vertices [20]. Both anatase and rutile have a t...

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Mo doped TiO₂: impact on oxygen vacancies, anatase phase stability and photocatalytic activity

et al. 2020

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“…Figure 7 shows the up-conversion (UC) luminescence spectra of the NS and QS100 ceramics samples excited under 980 nm laser. These samples exhibit two characteristic emission peaks of Ho 3+ around 520-580 and 650-700 nm [39]. The energy-level diagrams of Ho 3+ ions, as well as the possible UC pathways in the NBT-6BT:Ho 3+ lead-free piezoelectric ceramics under the excitation of 980 nm, are shown in Fig.…”

Section: Resultsmentioning

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“…8. When the ceramics samples are excited by 980 nm optical fiber laser, the electrons on the ground state 5 I 8 of Ho 3+ ions are excited to 5 I 6 via the ground state absorption (GSA) [39,40,41]. Then, a part of excited electrons on the 5 I 6 level will be further excited to the 5 F 4 / 5 S 2 level by excited-state absorption (ESA) and then generates green emission by radiative transition to 5 I 8 level.…”

Section: Resultsmentioning

confidence: 99%

Effects of defect on thermal stability and photoluminescence in quenched Ho‐doped 0.94Na0.5Bi0.5TiO3–0.06BaTiO3 lead‐free ceramics

Zheng

Chen

Jiang

et al. 2021

Journal of Materials Research

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Solid solution 0.94Na 0.5 Bi 0.5 TiO 3 -6BaTiO 3 (NBT-6BT) is considered to be one kind of lead-free piezoelectric materials with excellent electrical properties due to the existence of morphotropic phase boundary (MPB). However, its relatively lower depolarization temperature is a long-standing bottleneck for the application of NBT-based piezoelectric ceramics. In this work, the influence of thermal quenching on depolarization temperature and electrical properties of rare-earth Ho-doped NBT-6BT lead-free ceramics was investigated. It was shown that the relative high piezoelectric performance, as well as an improvement of depolarization temperature (T d ), can be realized by thermal quenching. The results showed that the quenching process induced high concentration of oxygen vacancy, giving rise to the change of octahedra mode and enhanced lattice distortion, which is benefit to the temperature stability of piezoelectric and ferroelectric properties. Furthermore, upconversion photoluminescence (PL) of Ho-doped NBT-6BT could be effectively tuned by the introduction of oxygen vacancy, suggesting a promising potential in optical-electrical multifunctional devices.

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“…As one of the most powerful luminescent nanocrystals, upconversion nanoparticles (UCNPs) have received extensive attention owing to their advantages of multicolor, narrow bandwidth, and no photobleaching, 1 due to which they have been extensively applied for background-free imaging, biological detection labeling, 2,3 temperature sensing, 4 and solar cells with enhanced infrared absorption. 5 They have been confirmed to be very efficient in the detection of glutathione, 6 DNA, 7 disease biomarkers, 8 metal ions, 9–11 and dyes.…”

Section: Introductionmentioning

confidence: 99%

Nanoporous fluorescent sensor based on upconversion nanoparticles for the detection of dichloromethane with high sensitivity

Wang

Zhan

et al. 2021

RSC Adv.

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Effects of calcination temperature and Li+ ions doping on structure and upconversion luminescence properties of TiO2:Ho3+-Yb3+ nanocrystals

Cited by 20 publications

References 37 publications

Mo doped TiO₂: impact on oxygen vacancies, anatase phase stability and photocatalytic activity

Mo doped TiO₂: impact on oxygen vacancies, anatase phase stability and photocatalytic activity

Effects of defect on thermal stability and photoluminescence in quenched Ho‐doped 0.94Na0.5Bi0.5TiO3–0.06BaTiO3 lead‐free ceramics

Nanoporous fluorescent sensor based on upconversion nanoparticles for the detection of dichloromethane with high sensitivity

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Effects of calcination temperature and Li+ ions doping on structure and upconversion luminescence properties of TiO2:Ho3+-Yb3+ nanocrystals

Cited by 20 publications

References 37 publications

Mo doped TiO2: impact on oxygen vacancies, anatase phase stability and photocatalytic activity

Mo doped TiO2: impact on oxygen vacancies, anatase phase stability and photocatalytic activity

Effects of defect on thermal stability and photoluminescence in quenched Ho‐doped 0.94Na0.5Bi0.5TiO3–0.06BaTiO3 lead‐free ceramics

Nanoporous fluorescent sensor based on upconversion nanoparticles for the detection of dichloromethane with high sensitivity

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Mo doped TiO₂: impact on oxygen vacancies, anatase phase stability and photocatalytic activity

Mo doped TiO₂: impact on oxygen vacancies, anatase phase stability and photocatalytic activity