J. Manam

Structural and photoluminescence studies of Eu3＋ doped zinc oxide nanorods prepared by precipitation method

Abstract Trivalent europium doped zinc oxide (ZnO:Eu3+) nanocrystals were synthesized via room temperature chemical co-precipitation and they were systematically characterized by means of X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and photoluminescence (PL) spectroscopy. The as-synthesized samples were found to have hexagonal wurtzite coexisted with the intermediate Zn5(OH)8Cl2·H2O phase, while the single hexagonal phase was facilitated due to the calcinations. The as obtained samples were broadly composed of nanoflakes while the highly crystalline nanorods were formed due to low temperature annealing of the as-synthesized samples. The crystallite size of the nanoflakes and nanorods (40–90 nm) were extracted from the XRD pattern which was found to be consistent with scanning electron microscopy (SEM) measurements. The photoluminescence (PL) spectra of nanophosphors showed bright red and orange emissions at 618 and 594 nm respectively with efficient broad blue green emission spectrum due to ZnO lattice. Further, a good energy transfer process from ZnO host to Eu3+ was observed in PL emission and excitation spectra of Eu3+ doped ZnO ions. In all, the present nanophosphors were found to have great potentiality for bio-applications.

Structural and spectroscopic diagnosis of ZnO/SnO2 nanocomposite influenced by Eu3+

Abstract Europium doped ZnO/SnO 2 nanocomposite phosphors were synthesized via room temperature co-precipitation method. In this work structural changes, optical properties and the associated photoluminescence response were investigated for different compositions of ZnO and SnO 2 activated with Eu 3+ ions. The prepared samples were systematically characterized by means of X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), field emission scanning electron microscopy for obtaining the structural information about the prepared materials. Diffuse reflectance (DR) UV-Vis spectrometer and photoluminescence (PL) spectroscopy technique were employed for studying the optical properties of prepared materials. XRD results confirmed the presence of both phases, hexagonal ZnO as well as tetragonal SnO 2 simultaneously and further using Debye Scherrers and Hall-Williamson relations, crystallite size were estimated and it was found to be in the range of 8–14 nm. The FTIR studies revealed the presence of different stretching and bending modes of Zn–O and Sn–O with an additional stretching and bending vibration of absorbed water (O–H) molecules. FESEM images suggested that the particle size lied in the range of 50 to 70 nm, which were almost spherical in shapes. A long range multi colour emission from blue to red region was observed for the 320 nm excitation wavelength. The observed emission involved sharp emission due to 5 D 0 → 7 F 1 transition that corresponded to the magnetic dipole transition. The study showed that the Eu 3+ doped nanocomposite was more suitable material than singly Eu 3+ doped ZnO and Eu 3+ doped SnO 2 with enhanced opto-electronic and luminescence properties and potential applications in display devices.

Influence of heat treatment on the structural and optical properties of SrGd2O4:Eu3+ phosphor

Abstract Novel red emitting Eu3+ doped SrGd2O4 phosphors were synthesized by homogeneous precipitation method followed by a subsequent combustion process at various temperatures. A systematic study on the consequent structural evolution and optical properties were investigated as a function of various processing temperatures. With the enhancement of processing temperature, SrGd2O4 phosphor showed a gradual transformation from a mixed phase to monophasic nature, with minimized volatile impurities. The microscopic images exhibited homogeneous aggregates of varying shapes and sizes with an average length of about 0.5–5 μm. Eu3+ doped SrGd2O4 phosphors prepared at low temperatures, showed miserably low values of red emission upon UV excitation owing to the presence of volatile impurities. The SrGd2O4:Eu3+ phosphors prepared at relatively high temperature exhibited strong red-orange emissions due to homogeneously occupied Eu3+ ions in the host lattice. The dominant red to orange (R/O) emission intensity ratios and CIE parameters of Eu3+ ions substantiated the site occupation of higher asymmetry sites of Gd3+ ions and the strong covalent nature. Dexter theory and critical distance calculation suggested that the dipole-dipole interaction could be responsible for the concentration quenching of Eu3+ (4 mol.%) doped SrGd2O4 phosphors. Elevated physical and chemical durability and stable photoluminescence made these phosphors suitable for white LEDs and other display applications.