Investigation of Fluorescence Yield of Phosphors in Vacuum Ultraviolet Region

Abstract

A theoretical model describing the dependence of quantum efficiency of a phosphor on the intensity of exciting radiation is developed. This model takes into account three dominant processes contributing to the loss of radiation when the host is excited by vacuum ultraviolet radiation above its bandgap energy, and fluorescence occurs through transfer of radiation from the host to the activator ions. The three processes are depletion of the ground state, nonradiative energy transfer in the excited state, and surface recombination of electron-hole pairs. It has been shown that the surface recombination effect can be treated adequately by assuming that the excited state lifetime of the host material is modified by a loss factor associated with this effect. © 2004 The Electrochemical Society. All rights reserved.

Inverse bottleneck in Eu2+–Mn2+ energy transfer

“…Thermal effects are found to be negligible by analyzing the Mn 2+ emission green shift and intensity versus temperature; the 150 1C efficiency of HALO is 490% of the room temperature value. Given the literature on the saturation of Mn 2+ phosphors whose main cause is the slow Mn 2+ emission (t$11.3 ms in HALO) [12][13][14][15][16][17], it is reasonable to assign the Mn 2+ quenching of HALO in these pcLEDs to saturation. However, standard models cannot explain the Eu 2+ quenching due to the fast radiative decay time of Eu 2+ (t$580 ns for Ca 5 (PO 4 ) 3 Cl:Eu 2+ ), and experiments with Eu 2+ phosphors in similar pcLEDs show virtually no quenching with variations in the LED excitation duty cycle.…”

“…6); a single exponential fit to the Mn 2+ decay profile in HALO-coated pcLEDs has t ¼ 9.6 ms versus spectrometer measurements of 11.3 ms. The faster decay is indication that energy transfer to the Mn 2+ -excited state also occurs between excited Mn 2+ ions [13,17,20].…”

Effects of the surface coating of BaMgAl10O17:Eu2+ phosphor with SiO2 nano-particles

“…Likewise, the vaccum UV radiation of 147 nm (8.43 eV) from Xe discharge excites the BAM host with a band gap [12] of 6.5 eV and generates free electronhole (e-h) pairs. As a consequence, the luminance can be improved by surface-related effects such as a decrease in the nonradiative recombination of e-h pairs [13] However, there is still no direct evidence in favor of this mechanism in the SiO 2 -coated BAM system. To do it, we cannot but resort to a powerful tool for detecting defects such as the electron spin resonance (ESR) system.…”

Investigation of host-to-activator energy transfer and surface losses in SrY2O4:Eu3+ under VUV excitation

“…It has been shown that if the excitation density is below saturation, and in the absence of surface losses, the transfer efficiency can be modeled using first-order competition kinetics between trapping at the activator and trapping at bulk killers [1,[11][12][13],…”

“…Mishra and Raukus [11] have presented a detailed theoretical treatment of host lattice excitation processes that includes a consideration of losses to surface states. They obtain an expression like the one presented above that also contains additional terms,…”