ABSTRACT
The τ-phase Ba1.3Ca0.7-x-y SiO4:xDy 3+/yTb3+ phosphors co-doped with Dy 3+ (x = 0.03) and Tb3+ (y = 0.01-0.05) trivalent rare-earth ions were prepared by the gel-combustion method. The structure-property relation of the samples was examined by X-ray diffraction, scanning electron microscopy and spectrophotometer. Here, the effect of Tb3+'s concentration on the spectroscopic properties of Ba1.3Ca0.7-x-y SiO4:xDy 3+/yTb3+ phosphors was explored by using the photoluminescence excitation, emission and decay curves. Importantly, the photonic energy transfer from (Dy 3+:4F9/2 + Tb3+:7F6) to (Dy 3+:6H15/2 + Tb3+:5D4) was observed, in which the Dy 3+ ions act as a light-emitting donor whereas the Tb3+ ions as a light-absorbing acceptor, resulting in an enhanced emission from the co-doped Ba1.3Ca0.7-x-y SiO4:xDy 3+/yTb3+ (x = 0.03 and y = 0.01-0.05) phosphors. Finally, the chromaticity coordinates were determined from the measured emission spectra, locating at the green and white light regions. This observation indicates that the characteristic emission colour could be tuned from white to green by varying Tb3+ concentrations under ultraviolet light.
ABSTRACT
Trivalent dysprosium/europium-codoped silicate phosphors (Ba1.3Ca0.7x-ySiO4:xDy3+/yEu3+) were prepared as a function of Eu3+concentration (x= 0.03 andy= 0.01-0.05). The phosphors showed the averaged crystallite size of â¼37.2 ± 1.3 nm and displayed nano-/micro-scale grains with some void defects. The energy bandgap is about 4.3 eV for co-doped samples and 3.2 eV for the silicate host. The photoluminescence spectra indicated that the presence of Eu3+ions enhanced the red light emission, and the emission peaks located at the versatile wavelengths of 482, 577, 592, 614, 652, and 703 nm. Then, the internal quantum efficiencies were estimated by using the Judd-Ofelt model. Resultantly, the best quantum efficiency was â¼74% when the doping concentrations were 3 mol% Dy3+and 4 mol% Eu3+ions. Finally, the CIE coordinate data exhibited that the emission color could be tuned from white to reddish-orange by changing the Eu3+contents, proposing the applicability of Ba1.3Ca0.7-x-ySiO4:xDy3+/yEu3+phosphors to the solid-state lighting.
ABSTRACT
This work report the influence of Eu3+ ion concentration on the photophysical properties of zirconia nanocrystal rods including its intrinsic quantum efficiency (IQE). A simple chemical route was employed in the synthesis procedure. X-ray diffraction results show mixed phases of monoclinic and tetragonal structures. Phase transition occurred at low (1 mol%) and high (7 and 8 mol%) Eu3+ concentrations. There are three forms of excitations for this phosphor; band edge excitation at 216 nm, charge transfer state transition at 247 and 263 nm, and direct excitation at 362, 395 and 535 nm. Photoluminescence emission for all the doped samples at room temperature appeared to be entirely from intraconfigurational Eu3+ emissions and depends both on the site symmetry as well as the Eu3+ concentration. Low temperature measurements indicate the presence of defect bands associated with oxygen vacancies. Defects were also shown to be temperature dependent. The Eu3+ ions were distributed in both phases especially at high ion concentrations (7 and 8 mol% Eu3+). Two multipolar processes where found to be responsible for the luminescence quenching process in the mixed-structure; the dipole-dipole and the dipole-quadrupole transitions. The intensity parameters (Ω2, Ω4), asymmetry ratio, R0 and the average decay lifetime of the nanocrystals show dependence on concentration and excitation wavelength. High IQE values were obtained at 1, 7 and 8 mol% Eu3+ where the monoclinic phase is dominant. The CIE coordinates values are comparable to existing red phosphors and in combination with high average IQE of 55% makes this phosphor a good candidate for red emitting phosphor application.
