Uniform red-phosphor spheres (∼60−300 nm in diameter) of Y2O3:Eu3+ binary and (Y,Gd)2O3:Eu3+ ternary systems exhibiting excellent emission at 610 nm have been converted from their colloidal precursor spheres synthesized via homogeneous precipitation. The precursor spheres (approximate composition: [(Y1-xGdx)1-yEuy](OH)CO3·1.3H2O, x = 0−0.5 and y = 0−0.11) are directly solid solutions, but arising from sequential nucleation each of the spheres has more Gd and especially Eu while having less Y going from the particle surface to the core. Eu3+ is more effective than Gd3+ in raising nucleation density, leading to rapidly decreased average size of the precursor particles at a higher Eu3+ addition. Diminishing the concentration gradients through adequate annealing is identified to be crucial to high luminous intensity of the oxide particles. At the optimal annealing temperature of 1000 °C, cation homogenization is achieved and the oxide particles largely retain their precursor morphologies, yielding dispersed u...

Monodispersed Colloidal Spheres for Uniform Y2O3:Eu3+ Red-Phosphor Particles and Greatly Enhanced Luminescence by Simultaneous Gd3+ Doping

Ce3+/Mn2+-coactivated Ca2Gd8(SiO4)6O2 (CGS) oxyapatite phosphors have been prepared via high temperature solid state reaction process. The Ce3+ emission at different lattice sites has been identified and discussed. The energy transfer from Ce3+ to Mn2+ in CGS:Ce3+/Mn2+ phosphors has been validated and demonstrated to be a resonant type via a dipole-quadrupole mechanism, and the critical distance (RC) calculated by quenching concentration method and spectral overlap method are 9.4 A and 9.2 A, respectively. A color-tunable emission in CGS:Ce3+/Mn2+ phosphors can be realized by the modulation of excitation wavelengths, namely, the change of Ce3+ emission at different lattice sites and the relative PL intensity of Ce3+ and Mn2+. In addition, the cathodoluminescence (CL) properties of CGS:Ce3+/Mn2+ phosphors including the CL spectra, the dependence of CL intensity on accelerating voltage and filament current, the decay behavior of CL intensity under electron bombardment, and the stability of CIE chromaticity coordinate have been investigated in detail. The results indicate that the as-prepared CGS:Ce3+/Mn2+ phosphors have a good CL intensity stability and CIE coordinate stability with a color-tunable emission from blue to yellow, crossing the white area by the energy transfer from Ce3+ to Mn2+ under low-voltage electron beam excitation. In conclusion, the wide-ranged white light with varied hues have been obtained in Ce3+ and Mn2+ coactivated CGS phosphors by utilizing the principle of energy transfer and properly designed activator contents as well as the selection of excitation wavelength under UV (287–352 nm) and low-voltage (1–7 kV) electron beam excitation. Therefore, the CGS:Ce3+/Mn2+ phosphors may potentially be used as single-phased white/yellow-emitting phosphor for UV LEDs (light emitting diodes) and FEDs (field emission displays).

Tunable luminescence of Ce3+/Mn2+-coactivated Ca2Gd8(SiO4)6O2 through energy transfer and modulation of excitation: potential single-phase white/yellow-emitting phosphors

The influence of processing parameters on luminescent oxides produced by combustion synthesis

Luminescent properties of Li+ doped nanosized Y2O3:Eu

Role of the surface in luminescent processes.

A theoretical expression for the brightness of powder phosphor is derived in order to investigate the effects of phosphor’s properties on low-energy cathodoluminescence. It contains the particle size, surface recombination rate, lifetime of holes, carrier diffusion coefficients, and anode voltage. As such, it can be applied to systematically optimize the design parameters of phosphors for maximum efficiency at low-voltage excitation. Use of the given expression is illustrated and a typical case is analyzed in this study.

Jong Duk Lee

Papers

The effects of particle size and surface recombination rate on the brightness of low-voltage phosphor