J. Suresh Kumar

Temperature-, power-, and concentration-dependent two and three photon upconversion in Er3+/Yb3+ co-doped lanthanum ortho-niobate phosphors

Lanthanum ortho-niobate matrices, LaNbO4 (LNO), doped with rare-earth ions (Er3+ and Yb3+), were prepared by a high-temperature solid-state reaction method. The LNO matrices thus prepared were confirmed by X-ray diffraction followed by Rietveld refinement. Raman spectroscopy was used to analyze the vibrational energy of the undoped and rare-earth doped LNO ceramics. The upconversion fluorescence was studied in the co-doped samples using an NIR laser (980 nm) at low and high pump power as well as the effect of sample temperature. The effect of the laser power and concentration of Yb3+ ions on the fluorescence properties were elucidated. The upconversion obtained was found to be due to two as well as three photon processes. Temperature-dependent upconversion measurements were performed to elucidate the nature of the emission processes, and it was concluded that two and three photon upconversion processes have different behaviors.

Highly efficient upconversion of Er 3+ in Yb 3+ codoped non-cytotoxic strontium lanthanum aluminate phosphor for low temperature sensors

Er3+ and Er3+/Yb3+ melilite-based SrLaAl3O7 (SLA) phosphors were synthesized by a facile Pechine method. The differences in emission intensities of 4I13/2 → 4I15/2 transition in NIR region when excited with Ar+ and 980 nm lasers were explained in terms of energy transfer mechanisms. Temperature and power dependence of upconversion bands in the visible region centered at 528, 548 and 660 nm pertaining to 2H11/2, 4S3/2 and 4F9/2 → 4I15/2 transitions were investigated. Fluorescence intensity ratio (FIR) technique was used to explore temperature sensing behaviour of the thermally coupled levels 2H11/2/4S3/2 of Er3+ ions in the phosphors within the temperature range 14–300 K and the results were extrapolated up to 600 K. Anomalous intensity trend observed in Er3+ doped SLA phosphor was discussed using energy level structure. Cytotoxicity of phosphors has been evaluated using 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay in Bluegill sunfish cells (BF-2). The non-cytotoxic nature and high sensitivity of the present phosphors pay a way for their use in vitro studies and provide potential interest as a thermo graphic phosphor at the contact of biological products.

Nanocrystalline ZnO–SnO2 mixed metal oxide powder: microstructural study, optical properties, and photocatalytic activity

In this study, nanocrystalline ZnO–SnO2 mixed metal oxide powder was prepared by co-precipitation using Zn(CH3COO)2∙2H2O and SnCl4∙5H2O as precursor materials. The powder was characterized by X–ray diffraction, scanning electron microscopy, and Fourier transform infrared spectroscopy. Williamson–Hall method was used to evaluate the micro structural parameters of ZnO–SnO2 such as crystallite sizes and lattice strain. The photoluminescence property of the sample was studied at different temperatures (10–300 K). Results showed that the emission intensity decreases with temperature increasing. The photocatalytic activity at the gas–solid interface was assessed by monitoring the degradation of nitrogen oxides, a major atmospheric pollutant. The results show that the nanocrystalline ZnO–SnO2 mixed metal oxide powder exhibits higher and more stable photocatalytic activity against photocorrosion than ZnO alone.Graphical abstract

Structural and impedance spectroscopy characteristics of BaCO3/BaSnO3/SnO2 nanocomposite: observation of a non-monotonic relaxation behavior

A BaCO3/BaSnO3/SnO2 nanocomposite has been prepared using a co-precipitation method without adding any additives. The prepared sample was characterized by using X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), scanning electron microscopy (SEM), Fourier-transform infrared (FT-IR) spectroscopy, energy dispersive X-ray spectroscopy (EDS) and Raman spectroscopy. Detailed studies on the dielectric and electrical behavior (dielectric constant, complex impedance Z*, ac conductivity, and relaxation mechanisms) of the nanocomposite have been performed using the nondestructive complex impedance spectroscopy technique within the temperature range 150–400 K. The dielectric constant of the sample as a function of temperature showed the typical characteristics of a relaxor. The maximum dielectric constant value was observed to depend on frequency. The non-monotonic relaxation behavior of the prepared nanocomposite was evidenced from the spectra of loss tan, tan(δ). The relaxation kinetics was modeled using a non-Arrhenius model.

Er 3+ doped calcium fluoroborate glasses for fiber amplifiers

Calcium fluoroborate glasses doped with Er₂O₃ (CFBEr) were prepared by the conventional melt quenching technique with molar compositions of (42-x) B₂O₃ + 20 CaF₂ + 15 CaO + 15 BaO + 8 Al₂O₃ + x Er₂O₃ (x = 0.05, 0.1, 0.5, 1.0, 2.0 and 4.0). Optical absorption spectrum in the region 250-2500 nm was recorded by using UV-Vis-NIR spectrophotometer for 1.0 mol % Er₂O₃ doped CFBEr10 glass. The absorption spectrum revealed thirteen absorption bands corresponding to transitions originating from ground (⁴I_15/2) state of erbium ions to various excited states. Judd-Ofelt (J-O) analysis has also been carried out from the experimental oscillator strengths (f_exp) to evaluate the JO intensity parameters (Ω₂, Ω₄ and Ω₆) and the calculated oscillator strengths (f_cal). Radiative parameters like radiative transition probabilities (A_R), total radiative transition probabilities (A_T), branching ratios (β_R) and radiative lifetimes (τ_R) were calculated for different excited states of Er³⁺ ion in CFB glasses. McCumber theory has been adapted to predict the emission cross-section of the NIR emission peak (⁴I_13/2 → ⁴I_15/2) at 1.53 μm. NIR luminescence spectra were recorded for all the glasses by exciting the samples with 980 nm diode laser and compared with that of the predicted emission cross-section. Variation of intensity as well as FWHM of the NIR emission transition has been studied for the utilization of these glasses in fiber amplifiers.