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This study presents Ce doping induced defect states in the SrZnO2 system, probed through X-ray absorption spectroscopy, electronic spin resonance and thermoluminescence (TL) analysis. The local electronic structure at the Zn and Sr K-edge reveals distortion upon Ce incorporation in the SrZnO2 system, whereas extended X-ray absorption fine structure analysis at the Ce L3-edge shows an increase in Ce–O bond length with increasing Ce doping concentration, which indicates that Ce occupies Zn sites at low doping concentration and Sr sites at higher doping concentration. The previous investigations (Manju et al., Appl. Phys. Lett., 2021, 119, 121108) of this system indicated the presence of a mixed valence state of Ce in SrZnO2, comprised of singly occupied 4f1 and empty 4f0 states. Owing to the differences in valence state, Ce incorporation results in the formation of cation vacancies and oxygen interstitial defects in the system, and thereby the system exhibited a new feature in gamma irradiated TL glow curves. The variation in intensity of the doping induced feature in the glow curves is evidence of the variation in 4f0/4f1 ratio of Ce energy levels. Hence, the combined analyses is comprehending the traits of the dopant and doping induced intrinsic defects, which will help in predicting the applicability of the material for lighting and scintillation devices. [ABSTRACT FROM AUTHOR]

This study reports host-controlled luminescence from 4f0 and 4f 1 Ce levels in SrZnO2, probed through x-ray absorption near edge and photoluminescence spectroscopies. O K-edge perceived the presence of Ce 4f states at the bottom of conduction band and 5d states merging with conduction band. Due to such an arrangement, a fast radiative emission (11.15 ns, average) is observed through charge transfer excitation from host to empty 4f0 Ce levels. Ce content is found to vary the site occupancy, which is then modifying the population of 4f0 and 4f 1 energy states by altering Ce–O bond covalency. This study proposes the Ce-doped SrZnO2 system as a potential system for scintillators and lighting materials. [ABSTRACT FROM AUTHOR]

We studied the effect of Si-ion irradiation on Ge 2 Sb 2 Te 5 (GST) thin films. Amorphous GST thin films were irradiated with 80 MeV Si 6 + ions and studied using XRD, FESEM and UV–Vis-NIR measurements. After irradiation, we observed a slight increase in the particle size and a decrease in the optical bandgap. No phase transition from amorphous to crystalline was observed. Calculations using SRIM software provided insight into the possible reasons for the observed effects of swift heavy ions on GST. These minute changes in optical and micro-structural properties suggested that GST thin films were quite stable and radiation tolerant under the effect of 80 MeV Si ion irradiation. [ABSTRACT FROM AUTHOR]

Trap distribution in MgAl2O4 nanocrystals has been investigated by analyzing thermoluminescence (TL) glow curves upon UV-irradiation. To probe various defects and trap distribution with the growth of spinel phase and crystallinity, three different fuels viz. monoethanolamine (MEA), glycine and urea, were employed in the combustion synthesis and annealing was performed at 700 ∘C and 900 ∘C. MEA and glycine resulted in crystalline spinel phase in annealed samples, however, urea resulted in minor secondary phase of MgO with the spinel phase in pristine as well as annealed samples. The x-ray photoelectron spectroscopy informed the presence of minor concentration of C and N in addition to Mg, Al and O, which are expected to influence the various defects of MgAl2O4 samples. The TL glow curve broadening in pristine and 700 ∘C annealed samples inferred the presence of multiple closely distributed traps. Shallow traps were more populated with urea, while higher concentrations of deep traps were observed with MEA and glycine. Computerized glow curve deconvolution of the TL glow curves revealed various trapping parameters. The observed shallow and deep traps have been attributed to various electron and hole centres such as antisite defects, O− and F+ centres. The significant high temperature shift of glow curve maxima in 700 ∘C annealed samples, synthesized using MEA and glycine, might be due to the reorganization of the local energy levels with the growth of spinel phase. Quenching of TL intensity at 900 ∘C anticipated the defect annealing accompanied by clustering of existing defects. Electron spin resonance analysis probed the existence of F+, V− centres and the spin–spin interaction of electron/hole spins trapped at these centres with the nearby cations, and estimated the formation of paramagnetic defect clusters at 900 ∘C annealing. A schematic band model is proposed to illustrate the TL behaviour in MgAl2O4 nanocrystals. [ABSTRACT FROM AUTHOR]

Applicability of spinel compounds is mainly governed by cation distribution in them. In the presented study, thermally induced cation ordering is found to influence the emission color of Mg 2 + , Fe 3 + co-doped ZnAl 2 O 4 spinel. Cation distribution is monitored through Mg K-edge, Fe L 2 , 3 -edge, O K-edge X-ray absorption near edge structure spectroscopy and X-ray diffraction analysis using synchrotron radiation. Thermal treatment provided sufficient energy to Zn 2 + , Mg 2 + , Al 3 + and Fe 3 + cations to redistribute themselves on tetrahedral and octahedral sites, and reduce the octahedral distortion, thereby gaining stability. Reduced inversion accompanied by decrease in oxygen vacancies, while increase in tetrahedral and octahedral site vacancies contributed toward more intense blue emission band and quenched yellow band, changing the emission color from bluish-white to blue. Correlation derived between cation ordering and luminescence upon thermal treatment predict Mg 2 + , Fe 3 + co-doped ZnAl 2 O 4 nanophosphors to be useful in thermal sensing applications. [ABSTRACT FROM AUTHOR]

Thermoluminescence (TL) analysis of gamma-irradiated SrZnO2:Dy nanophosphors elucidates the presence of various trapping centers in forbidden band. Raman and Fourier-transformed infrared spectra indicate effect on vibrational structure upon doping. Complex glow curves are obtained at varying gamma radiation doses, exhibiting glow features in low (50-180 °C) and high (220-400 °C) temperature regions. The deconvolution of glow curves indicates the presence of TL peaks at =100, 143, 202, 269, and 337 =C. The effect of Dy doping is observed as emergence of new glow feature at =143 °C. The substitution of trivalent Dy into SrZnO2 host having divalent cations is proposed to be creating Dy1þ X (X = Sr, Zn) electron traps and V²X- hole traps, along with hitherto existing intrinsic defects. The concentration quenching of TL signal is perceived at 3 mol% Dy doping, whereas comparing glow curves for all samples at saturation dose indicate quenching of low- and high-temperature glow features at different doping concentrations. The theoretical track interaction model and empirical three trap one recombination center (3T1R) model is used to explain former and latter effects, respectively. A schematic band model is proposed to predict the trap distribution upon Dy inclusion, responsible for observed TL in SrZnO2:Dy nanophosphors. [ABSTRACT FROM AUTHOR]

The correlation of several defects and optical and magnetic properties with Fe content in Zn1−xFexAl2O4 (0.01 ≤ x ≤ 0.40) nanocrystals has been scrutinized through X‐ray diffraction, O K‐edge X‐ray absorption near‐edge structure, FT–IR, diffuse reflectance, photoluminescence and electron spin‐resonance spectroscopies, and vibrating sample magnetometry. Increasing Fe content causes elongation in the octahedral units of the lattice, accompanied by distortion in the octahedral coordination. Fe introduces non‐radiative centres in the forbidden gap, thereby tuning the band gap from 4.37 to 3.88 eV and eliminating emission in the visible region. Zn vacancies are found to tail off, while , and FeAl× antisite defects increase in concentration with increasing Fe content. Inhomogeneous broadening of spin‐resonance signals infers strong spin‐lattice interactions of Fe3+ ions at distorted octahedral and non‐symmetric tetrahedral sites. A transition is observed from paramagnetism to superparamagnetism at higher Fe concentrations. A visual colour change from pearly white to orange–brown is observed in Zn1−xFexAl2O4 nanocrystals with increasing Fe content, revealing its potential candidature for pigments in the paint and dye industries. [ABSTRACT FROM AUTHOR]

Complex cation distribution in spinel solid solution, fosters defect generation and permutates the optical properties. To scrutinize the effect on structural properties, viz. the cation distribution and defect states upon substitution of Zn with Mg; and to tune the emission properties, Zn1−xMgxAl2O4 (0.01 ≤ x ≤ 0.30) nanocrystals are synthesized. The nanocrystals show increased inversion and generation of multiple defects, namely zinc vacancies, zinc interstitials, oxygen vacancies and antisite defects with increasing Mg content, which thereby impacts the optical band gap. Pentahedral coordination in addition to tetra- and octahedral coordination of Al has been observed, which infers the presence of oxygen vacancies and dangling bonds. Moire fringes formation has intimated the presence of two or more crystal lattices with higher Mg substitution. Band-to-band and defect-assisted photoluminescence shows the role of multiple defects, especially defect clusters, in deciphering the properties of the resulting crystals. Color change from bluish-white to pink has been achieved depending upon the excitation wavelength and emission mechanism, as proposed through a band model schematic. The presented study may be beneficial for designing the Zn1−xMgxAl2O4 nanocrystals with optimized emission properties. [ABSTRACT FROM AUTHOR]

SrZnO2 nanophosphors synthesized using a combustion technique with monoethanolamine fuel exhibited unprecedented wavelength selective luminescence in the blue and white region. The presence of lattice defects in rod shaped nanophosphors was established using X-ray absorption spectroscopy (XAS), thermoluminescence (TL) and photoluminescence (PL). X-ray absorption near edge structure at the Zn and Sr K-edges revealed a mismatch in experimental and theoretically simulated absorption edges, which was ascribed to the effect of lattice defects present in the system. Extended X-ray absorption fine structure analysis showed the squeezing of Zn coordination polyhedra and lengthening of Sr coordination polyhedra, thereby causing disorder in the structure resulting in the tailing of band edges. The consequences of these effects were observed in energy dependent luminescence corresponding to the above and below band gap photo-excitation. This trend in PL was explained with a schematic band model depicting transitions involving shallow and deep trapping states leading to dual emission in the visible region. Such energy dependent emission proposes SrZnO2 as a potential candidate for solid state lighting and white light emitting devices. [ABSTRACT FROM AUTHOR]