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The article explores the photoluminescence properties of UV, near-UV and blue excited BaWO 4 : Eu3+ red phosphors. The optical band gap narrowing is observed after adding Eu3+ ions. The excitation spectra exhibit a broad peak centred at 255 nm and several narrow peaks of Eu3+ ions at 362, 382, 395, 415 and 465 nm. The three peaks located at 255 (UV), 395 (near-UV) and 465 nm (blue) are the most intense and suitable for the excitation of the sample. The spectral profile of the emission spectra irradiated at 255, 395 and 465 nm are identical. The brightest emission is realized at 18 mol% doping of Eu3+ ions at 255 and 465 nm excitations. However, the optimum concentration is 16 mol% at 395 nm excitation. The phosphors emit highly pure red lights with color purity 98.192%, 97.794% and 98.693% for the optimised concentration under UV, near-UV and blue excitations of 255, 395 and 465 nm, respectively. The quantum efficiency of BaWO 4 : 16 mol% Eu3+ phosphor is calculated as∼48.234% at 395 nm excitation. The emission intensity parameters are calculated in view of the Judd-Ofelt theory. The spectroscopic parameters like radiative transition probability, radiative lifetime, branching ratio and stimulated emission cross-section are further evaluated from the three emission spectra recorded at 255, 395 and 465 nm excitations. The derived results advocate the use of synthesized material as a red phosphor in white-LED, laser and display devices. [ABSTRACT FROM AUTHOR]

A series of white light emitting Pr3+ activated SrWO 4 phosphors are synthesized by most facile solid state reaction routes. The structural properties are investigated by X-ray diffraction (XRD) spectroscopy, Field Emission Scanning Electron Microscopy (FESEM), Energy dispersive X-ray (EDX) spectroscopy, Fourier transform infrared (FTIR) spectroscopy and X-ray photoemission spectroscopy (XPS). The optical properties are elaborated in detail using UV–visible–NIR spectroscopy and Photoluminescence (PL) spectroscopy. Rietveld refinement of obtained XRD data is performed to investigate the crystal structure and crystallographic parameters. The photoluminescence measurements ensure that the developed phosphors emit bright white light under UV excitation of 242 nm and blue excitation of 448 nm. The maximum emission intensity is achieved at 3 mol% doping of Pr3+, followed by concentration quenching due to dipole-dipole interactions. The decay of electrons from the most populated 3P 0 state in all the samples follows the single exponential nature. The average decay time varies in the same manner as the emission intensity with Pr3+ concentration. The color purities of the lights emitted from all the materials under 242 nm and 448 nm excitations are low (close to 10%) and hence suitable for white light. A bright white LED is successfully fabricated by coating the optimised phosphor SrWO 4 : 3 mol% Pr3+ on a 460 nm blue LED chip. The interesting results recommend that the proposed material can be used in developing single phase white-LED. [ABSTRACT FROM AUTHOR]

An array of Eu3+ doped Ba 2 GdSbO 6 luminescent materials have been synthesized by the conventional solid-state (high temperature) reaction route. Surface morphology has been studied via Field Emission Scanning Electron Microscopy. The structural and optical behaviors have been studied using X-Ray Diffraction (XRD), FTIR, Raman spectroscopy, Diffuse reflectance spectroscopy, Photoluminescence excitation (PLE), and Photoluminescence emission (PL) spectra. FTIR and Raman's spectra provided the chemical functional group and different vibrational levels within the samples. The calculated optical band gap was 4.40 eV and 4.47eV for pure and optimized samples respectively. Photoluminescence emission curves have been recorded for 245 nm of excitation wavelength and the highest emission peak was focused at 595 nm corresponding to 5D 0 → 7F 1. Similarly, the Photoluminescence excitation curves were monitored at the emission wavelength of 595 nm and a broad charge transfer band (CTB) was observed from 230 to 285 nm. The emission spectra show the concentration quenching effect beyond the 2 mol% Eu3+ concentration. The corresponding transitions of Eu3+ were further utilized to obtain the Judd-Ofelt (J-O) transition intensity parameters Ω λ (λ = 2, 4) for each sample. Additionally, by studying decay kinetics, the average lifetime of the red emission of the samples has been evaluated, which was 4.622 ms. The photometric study also reveals the CIE coordinates, color purity and CCT values of the proposed phosphor material. Thus, the results obtained from these characterizations, suggest that the prepared sample may behave as a potential candidate in the case of UV-excited red light-emitting phosphor material for light-emitting diodes and field emission devices. • Ba 2 GdSbO 6 : Eu3+ phosphors have been synthesized by solid-state reaction method. • Rietveld refinement has been carried out for better crystal structure analysis. • Raman studies for this host Ba 2 GdSbO 6 have been carried out for the first time. • The phosphors show intense photoluminescence emission with very high color purity. • Judd-Ofelt analysis has been done to understand the spectroscopic behavior of the proposed phosphor material. [ABSTRACT FROM AUTHOR]

A single phase white light emitting Dy doped LiCaBO phosphors were prepared by solid-state reaction method at 700 °C. The crystal structure properties were analyzed by utilizing powder X-ray Diffraction and followed by the profile fitting to calculate the lattice parameters. The FESEM, UV-Vis, photoluminescence excitation and emission spectra, decay time and quantum yield measurement were utilized to characterize the samples. The temperature dependent photoluminescence emission and decay times were recorded in the temperature range 100-480 K. The phosphor exhibits two emission bands at 485 nm (blue) and 578 nm (yellow) originating from the f-f transition of Dy. The optimized doping concentration for maximum emission intensity was 2 mol%. A near white emission was achieved with color co-ordinate (0.35, 0.39) and CCT value 4955 K. The material had excellent thermal and color stability. The absolute quantum yield is 0.25. So the near white emission, excellent thermal stability and suitable quantum yield of LiCaBO: Dy can be a promising candidate for near UV-LED pumped white light emitting diode. [ABSTRACT FROM AUTHOR]

Charge transfer band (CTB) transition significantly improves the photoluminescence properties of phosphor materials due to its higher absorption efficiency than the characteristic excitations of rare-earth ions. La 2 Zr 2 O 7 (LZO): Pr3+ phosphors with varying doping concentrations of Pr3+ were synthesized through the hydrothermal method. The formation of the pure pyrochlore phase was confirmed from powder X-ray diffraction (XRD). The structural analysis was performed from Rietveld refinement of the XRD data. Field emission electron microscope (FESM) equipped with EDX spectroscopy was used to study the surface morphology and elemental compositions. X-ray photoelectron spectroscopy (XPS) analysis of the optimized sample provides the bonding state of the compositions. Under 257 nm CTB excitation, the photoluminescence emission spectra (PL) exhibit all the characteristic emission peaks of Pr3+ ion. The transitions involved in the excitation and emission process have been shown in the energy level diagram of Pr3+ ions. The Concentration quenching effect was explained from Bless relation and Dexter energy transfer theory between activator ions. Decay curves of the prepared phosphors show bi-exponential behavior. The up-conversion emission spectra were recorded under 980 nm laser excitation. The optical transition in the UV–Vis range was investigated based on the diffuse reflectance spectra, and the results match well with the excitation spectra. The photometric study informs the color and the quality of the emitted light. The outcomes produce a new synthesis method to prepare La 2 Zr 2 O 7 :Pr3+ nano phosphor that can be an excellent candidate for solid-state lighting and UV/NIR to the visible converter in solar cell applications. [Display omitted] [ABSTRACT FROM AUTHOR]

Abstract: Here in, the synthesis of the terbium doped zinc oxide (ZnO:Tb3+) nanorods via room temperature chemical co-precipitation was explored and their structural, photoluminescence (PL) and thermoluminescence (TL) studies were investigated in detail. The present samples were found to have pure hexagonal wurtzite crystal structure. The as obtained samples were broadly composed of nanoflakes while the highly crystalline nanorods have been formed due to low temperature annealing of the as synthesized samples. The diameters of the nanoflakes are found to be in the range 50–60nm whereas the nanorods have diameter 60–90nm and length 700–900nm. FTIR study shows Zning band at 475cm−1 showing improved crystal quality with annealing. The bands at 1545 and 1431cm−1 are attributed to asymmetric and symmetric Cing vibration modes. The diffuse reflectance spectra show band edge emission near 390nm and a blue shift of the absorption edge with higher concentration of Tb doping. The PL spectra of the Tb3+-doped sample exhibited bright bluish green and green emissions at 490nm (5D4 → 7F6) and 544nm (5D4 → 7F5) respectively which is much more intense then the blue (450nm), bluish green (472nm) and broad green emission (532nm) for the undoped sample. An efficient energy transfer process from ZnO host to Tb3+ is observed in PL emission and excitation spectra of Tb3+-doped ZnO ions. The doped sample exhibits a strong TL glow peak at 255°C compared to the prominent glow peak at 190°C for the undoped sample. The higher temperature peaks are found to obey first order kinetics whereas the lower temperature peaks obey 2nd order kinetics. The glow peak at 255°C for the Tb3+ doped sample has an activation energy 0.98eV and frequency factor 2.77×108 s−1. [Copyright &y& Elsevier]

In this article, photoluminescence up and down conversion properties of Er3+ activated Y 2 Zr 2 O 7 (YZO) phosphors have been investigated. All the compositions have been synthesized via hydrothermal method. Various characterization techniques have been used to characterize the samples. Powder X-ray diffraction reveals the crystallization of the fluorite phase of all samples. FESEM technique and EDX spectroscopy were performed for surface morphology and elemental analysis of the samples. The optical band gap is appeared to increase after doping. Photoluminescence down conversion (DC) excitation (PLE) spectra exhibit a strong near UV absorption at 378 nm. All the doped samples under 378 nm excitation display the featured emission of Er3+ ions. The variation of DC PL intensity and the lifetimes with temperature were also investigated within the temperature range 77K–475K. Excitation power dependent up conversion (UC) emission and temperature dependent UC emission spectra within 303K–483K of the optimized sample were examined with 980 nm laser excitation. The fluorescence intensity ratio (FIR) technique and the variation of the average lifetime with temperature have been used to study the temperature sensing behaviour of the reported phosphors. Comparatively high sensitivities suggest the reported phosphors could have potential applications in temperature sensing and also could be a UV and NIR to green converter phosphors material. Image 1 • A class of Er3+ doped Y 2 Zr 2 O 7 phosphors was designed through the hydrothermal method. • Up and down conversion photoluminescence characteristic of the synthesized phosphors were examined in detail. • Influence of temperature on both up and down conversion emission was investigated. • The maximum relative temperature sensitivity (Sr) reached up 1.57% K−1 at 250 K for DC emission. [ABSTRACT FROM AUTHOR]

Ceramic phosphors of pure, Dy3+ doped, and Li+ co-doped SrWO 4 have been prepared by solid state reaction route. The structural investigation was conducted with X-ray diffractometer (XRD), Fourier transform infrared spectroscopy (FTIR), and Field emission scanning electron microscope (FESEM). The XRD results verify the phase purity and the crystallinity of the synthesized materials and the vibrational bands of SrWO 4 lattice are confirmed by FTIR. FESEM images show the irregular spherical morphology of the material. However, the particles get agglomerated after the doping of Dy3+ and Li+ ions. The optical measurement was conducted with UV–Visible and Photoluminescence spectrophotometer. The photoluminescence emission spectra contain two bright peaks at 480 nm and 575 nm and a faint peak at 665 nm under 351 nm excitation. The optimum emission is obtained at 2 mol% doping of Dy3+ions. The emission intensity is increased up to three times with the incorporation of Li+ ion. The photometric study reveals that the material emits white and yellow lights. The temperature dependent photoluminescence studied within the temperature range of 77 K–475 K demonstrates that the emission at higher temperatures is much intense than that at room temperature. Therefore, the above material can be developed as a phosphor for application in display devices and LEDs above room temperature. [Display omitted] • SrWO 4 : Dy3+/Li+ phosphors are synthesized by solid state reaction route. • The emission intensity is enhanced three times with the incorporation of Li + ions. • The material shows the abnormal temperature dependent photoluminescence emission. • The emission intensity at 475 K is almost 5 times the emission intensity at 300 K. [ABSTRACT FROM AUTHOR]