Studies on a novel SrZr2 CaLa2 O8 :Eu3+ phosphor for lighting applications emitting direct white light.

Direct white light emitting phosphors play a significant role in the display industry due to their ability to improve the quality, efficiency, and versatility of lighting sources used in most of the displays. The currently investigated phosphor SrZr2 CaLa2 O8 :Eu3+ was prepared by a conventional solid-state reaction method. It has been observed that the stoichiometric ratio of all precursors plays an important role in determining the characteristics of the final phosphor. From X-ray diffraction (XRD) analysis, the phosphor was observed to have a hexagonal phase and a crystal size of ~28 nm. Scanning electron microscopy (SEM) observations revealed a cluster of rod-like structures with an average diameter of ~0.2 µm. The excitation peak maximum observed at 280 nm is due to charge transfer between Eu3+ -O2- ions. The energy transitions 7 F0 → 5 L6 and 7 F0 → 5 D2 are responsible for the appearance of other excitation peaks at ultraviolet (UV) (395 nm), blue (~467 nm), green (~540 nm), orange (~590 nm), and red (~627 nm) attributed to 5 D0 → 7 FJ (J = 0-4) transitions of europium ion (Eu3+ ). The Commercial International de I'Eclairage (CIE) chromaticity coordinates were estimated to be (0.37, 0.0.33) and (0.67, 0.33) for the emissions corresponding to 395 and 590 nm, respectively. The characteristic emissions of Eu3+ ions allow this novel phosphor to be used to generate direct white light in light-emitting diodes (LEDs), which is otherwise difficult to achieve in single-component systems.

Europium doped Sr2 YNbO6 double perovskite phosphor for photoluminescence and thermoluminescence properties.

A luminescent double perovskite phosphor Sr2 YNbO6 doped with Eu3+ crystallized to the monoclinic phase and was synthesized successfully via a conventional high-temperature combustion method. The formation of the crystal structure, phase purity, and surface morphology were studied using X-ray diffraction patterns and scanning electron microscopy. The characteristic vibrations between the atoms of the functional groups present in phosphor were studied using Fourier transform infrared spectra analysis. The luminescence properties of the prepared phosphors were investigated in terms of photoluminescence (PL) and thermoluminescence (TL). PL excitation spectra exhibited charge transfer bands and the characteristic 4f6 transitions of Eu3+ . A prominent PL emission was obtained for the phosphor doped with 4 mol% Eu3+ under the 396 nm excitation wavelength. PL emission quenching was observed for the higher doping concentrations due to a multipole-multipole interaction. A highly intense PL emission arose due to the hypersensitive 5 D0 -7 F2 electric dipole transition of Eu3+ that dominated the emission spectra. The thermal stability of the phosphor was examined through temperature-dependent PL. The TL properties of the Sr2 YNbO6 double perovskites irradiated with a 90 Sr beta source at different doses were measured. The double perovskite phosphors under study showed a linear dose-response with increasing beta dose, ranging from 1 Gy to 10 Gy. Trapping parameters of the TL glow curves were determined using Chen's peak shape method and computerized glow curve deconvolution (CGCD). CGCD fitting of the TL glow curves revealed that it was consisted of three major peaks and followed second-order kinetics. The estimated activation energies were determined using different methods and were comparable and significant.

Comparative Study of Photoresponse from Vertically Grown ZnO Nanorod and Nanoflake Films.

Zinc oxide (ZnO) based ultraviolet (UV) photodetectors have been fabricated and their photoresponse is studied in Schottky diode configuration. A cost-effective single-step electrochemical deposition method is adopted for the growth of ZnO film with nanorod (NR) and nanoflake morphology. A comparative study of the photodetection parameters based on surface trap states, crystallinity, and strain is done for two different morphology films. Significant photocurrent enhancement is observed for the nanorods under UV light, with appreciable photoresponse in the blue region. A template-assisted growth of ZnO NR film is proposed for better photoresponse and sensitivity of the device, useful for various optoelectronic applications.

Intense red-emitting Y4Al2O9:Eu3+ phosphor with short decay time and high color purity for advanced plasma display panel.

A new phosphor Y(4)Al(2)O(9):Eu(3+) (YAM:Eu(3+)) emitting intense monochromatic red at 612 nm under vacuum ultraviolet (VUV) and ultraviolet (UV) excitations has been developed for application in next generation plasma display panels (PDPs). The developed phosphor has better luminescence efficiency, colour purity and shorter decay time than commercial (Y,Gd)BO(3):Eu(3+) red emitting PDP phosphor. High color purity (x = 0.67, y = 0.32) under VUV excitation with short decay time (1.03 msec) and excellent stability against degradation during PDP panel preparation suggest that YAM:Eu(3+) is a potential candidate for present and future PDPs. Surface coating by SiO(2) further improved phosphor characteristics.