Cathodoluminescence of nanocrystalline Y2O3:Eu3+ with various Eu3+ concentrations

© The Author(s) 2014. Published by ECS. This is an open access article distributed under the terms of the Creative Commons Attribution 4.0 License (CC BY, http://creativecommons.org/licenses/by/4.0/), which permits unrestricted reuse of the work in any medium, provided the original work is properly cited.This article has been made available through the Brunel Open Access Publishing Fund.Herein a study on the preparation and cathodoluminescence of monosized spherical nanoparticles of Y2O3:Eu3+ having a Eu3+ concentration that varies between 0.01 and 10% is described. The luminous efficiency and decay time have been determined at low a current density, whereas cathodoluminescence-microscopy has been carried out at high current density, the latter led to substantial saturation of certain spectral transitions. A novel theory is presented to evaluate the critical distance for energy transfer from Eu3+ ions in S6 to Eu3+ ions in C2 sites. It was found that Y2O3:Eu3+ with 1–2% Eu3+ has the highest luminous efficiency of 16lm/w at 15keV electron energy. Decay times of the emission from 5D0 (C2) and 5D1 (C2) and 5D0 (S6) levels were determined. The difference in decay time from the 5D0 (C2) and 5D1 (C2) levels largely explained the observed phenomena in the cathodoluminescence-micrographs recorded with our field emission scanning electron microscope

Cathodoluminescence studies of phosphors in a scanning electron microscope

Cathodoluminescence studies are reported of phosphors in a field emission scanning electron microscope (FESEM). A number of phosphor materials have been studied and exhibited a pronounced comet-like structure at high scan rates, because the particle continued to emit light after the beam had moved onto subsequent pixels. Image analysis has been used to study the loss of brightness along the tail and hence to determine the decay time of the materials. This technique provides a simple and convenient way to study the decay times of individual particles

12CaO.7Al2O3 ceramic: A review of the electronic and optoelectronic applications in display devices

The alumina-based compound, 12CaO.7Al2O3, is a ceramic material with a unique cage-like lattice. Such a structure has enabled scientists to extract various new characteristics from this compound, most of which were unknown until quite recently. This compound has the ability to incorporate different anionic species and even electrons to the empty space inside its cages, thereby changing from an insulator into a conductive oxide. The cage walls can also incorporate different rare earth phosphor elements producing an oxide-based phosphor. All these characteristics are obtained without a significant change in the structure of the lattice. It is, therefore, reasonable to expect that this compound will receive attention as a potential material for display applications. This review article presents recent investigations into the application of 12CaO.7Al2O3 ceramic in various display devices, the challenges, opportunities and possible areas of future investigation into the development of this naturally abundant and environmental friendly material in the field of display.LP Displays Ltd, Blackburn, UK for partial funding of the studentship at Queen Mary, University of London. Dr Lesley Hanna of Wolfson Centre for Materials Processing, Brunel University Londo

Low-temperature solid-state synthesis and upconversion luminescence properties in (Na/Li)Bi(MoO4)2:Yb3+,Er3+ and Color Tuning in (Na/Li)Bi(MoO4)2:Yb3+,Ho3+,Ce3+ phosphors

In this Article, we reported the synthesis and the upconversion luminescence (UCL) properties of a series of novel (Na/Li)Bi(MoO4)(2):Yb3+,Er3+ [(N/L)BMO:Yb3+,Er3+] and (Na/Li)Bi(MoO4)(2):Yb3+,Ho3+,Ce3+ [(N/L)BMO:Yb3+,Ho3+,Ce3+] phosphors. X-ray diffraction patterns and Rietveld refinements for several representative samples indicated the pure phase of as-prepared samples. The Yb3+,Er3+ codoped (N/L)BMO presented bright green luminescence under 975 nm laser excitation with UCL spectra showing two main green bands around 529 nm (Er3+, H-2(11/2) -> I-4(15/2)) and 551 nm (Er3+, S-4(3/2) -> I-4(15/2)), in addition to a very weak one at 655 nm (Er3+, F-4(9/2) -> I-4(15/2)). The (N/L)BMO:Yb3+,Ho3+ mainly showed a green band around 544 nm (S-5(2),F-5(4) -> I-5(8)) and a red band around 654 nm (F-5(5) -> I-5(8)) upon 975 nm laser excitation. With increasing Yb3+ concentrations in (N/L)BMO:Yb3+,0.01Ho(3+), the red/green ratios decreased monotonously corresponding to the emission color variation from light red to light yellow. Both UCL mechanisms of Yb3+,Er3+ and Yb3+,Ho3+ were determined to be two-phonons absorption processes in (N/L)BMO:Yb3+,Er3+/Ho3+. The Ce3+ ions were introduced into Yb3+,Ho3+ codoped (N/L)BMO to show the color tuning from light yellow to light red originating from the cross relaxation processes of (CR1) Ho3+ (F-5(4), S-5(2)) + Ce3+ (F-2(5/2)) -> Ho3+ (F-5(5)) + Ce3+ (F-2(7/2)) and (CR2) Ho3+(I-5(6)) + Ce3+ (F-2(5/2)) -> Ho3+ (I-5(7)) + Ce3+ (F-2(7/2)), which is based on the energy matching of Ce3+2F7/2-F-2(5/2) level pairs with Ho3+5I6-I-5(7) and F-5(4),S-5(2)-F-5(5) level pairs and confirmed by the decay times. These results suggest good UCL properties of (N/L)BMO:Yb3+, Er3+ and (N/L)BMO:Yb3+, Ho3+, Ce3+ materials, and color modulation is easily controlled by varying Yb3+ concentration and a cross relaxation process between Ce3+ and Ho3+, which provides efficient methods to regulate the emission color of UCL phosphors

Effect of Li+-​ion on enhancement of photoluminescence in Gd2O3:Eu3+ nanophosphors prepared by combustion technique

Gd2O3:Eu3+ (4 mol​%) nanophosphor co-​doped with Li+ ions have been synthesized by low-​temp. soln. combustion technique in a short time. Powder X-​ray diffractometer (PXRD)​, SEM, Fourier transform IR spectroscopy (FT-​IR)​, UV-​VIS and photoluminescence (PL) techniques have been employed to characterize the synthesized nanoparticles. It is found that the lattice of Gd2O3:Eu3+ phosphor transforms from monoclinic to cubic as the Li+-​ions are doped. Upon 254 nm excitation, the phosphor showed characteristic luminescence 5D0 → 7FJ (J = 0-​4) of the Eu3+ ions. The electronic transition located at 626 nm (5D0 → 7F2) of Eu3+ ions was stronger than the magnetic dipole transition located at 595 nm (5D0 → 7F1)​. Furthermore, the effects of the Li+ co-​doping as well as calcinations temp. on the PL properties have been studied. The results show that incorporation of Li+ ions in Gd2O3:Eu3+ lattice could induce a remarkable improvement of their PL intensity. The emission intensity was obsd. to be enhanced four times than that of with out Li+-​doped Gd2O3:Eu3+