Manifestation of spin-dependent recombination in afterglow of zinc oxide crystals

Sun

2017

An energy conversion model has been established for the intrinsic persistent luminescence in solids related to the native point defect levels, formations, and transitions. In this study, we showed how the recombination of charge carriers between different defect levels along the zero phonon line (ZPL) can lead to energy conversions supporting the intrinsic persistent phosphorescence in solids. This suggests that the key driving force for this optical phenomenon is the pair of electrons hopping between different charged defects with negative-U. Such a negative correlation energy will provide a sustainable energy source for electron-holes to further recombine in a new cycle with a specific quantum yield. This will help us to understand the intrinsic persistent luminescence with respect to native point defect levels as well as the correlations of electronics and energetics.

Section: Cap Modelsupporting

confidence: 83%

Section: Znomentioning

confidence: 62%

Section: Existing Energy Transfer Mechanismmentioning

confidence: 99%

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Energy conversion modeling of the intrinsic persistent luminescence of solids via energy transfer paths between transition levels

Sun

2017

“…Usually, this involves increasing the defect concentration of materials in a packed structure. [84][85][86][87]…”

Section: S-richmentioning

confidence: 99%

Energy harvesting and conversion mechanisms for intrinsic upconverted mechano-persistent luminescence in CaZnOS

2016

We interpreted the mechanisms of energy harvesting and conversion for intrinsic upconverted mechano-persistent luminescence in CaZnOS through a native point defects study. We found that vacancy defects such as Zn and O vacancies, as well as Schottky pair defects, act as energy harvesting centers; they are very readily formed and very active. They are found to be extra deep electron or hole trap levels near the valence or conduction band edges, respectively. This leads to a coupling and exchange effect to continuously collect and transport host charges along a path via localized states to deep recombination levels. The initiating energy barrier is small and can be overcome by ambient thermal stimulation or quantum tunneling. Native activators such as V

“…Usually, sintering is a popular method for increasing the defect concentration by means of increasing the density of materials via a more densely packed structure, which has been reported in other experiments. [76][77][78][79] Another possible way to create neutral pair defects in a state of thermal disequilibrium is by using external stress, which can provide a similar effect to sintering. [80][81][82][83][84] According to the experiment on the persistent luminescence of Er 2 O 3 by Tanner et al, 14 we see that the decay of the emission at 660 nm has a half-life of about 0.25 s, whereas this is about 0.625 s for the decay at 1540 nm.…”

Section: Native Defects-induced Luminescence Propertiesmentioning

confidence: 99%

Unraveling energy conversion modeling in the intrinsic persistent upconverted luminescence of solids: a study of native point defects in antiferromagnetic Er₂O₃

2016

We investigated the mechanism of the intrinsic persistent luminescence of Er2O3 in the A-type lattice based on first-principles calculations. We found that the native point defects were engaged in mutual subtle interactions in the form of chemical reactions between different charge states. The release of energy related to lattice distortion facilitates the conversion of energy for electrons to be transported between the valence band and the trap levels or even between the deep trap levels so as to generate persistent luminescence. The defect transitions that take place along the zero-phonon line release energy to enable optical transitions, with the exact amount of negative effective correlation energy determined by the lattice distortions. Our calculations on the thermodynamic transition levels confirm that both the visible and NIR experimentally observed intrinsic persistent luminescence (phosphor or afterglow) are related to the thermodynamic transition levels of oxygen-related defects, and the thermodynamic transition levels within different charge states for these defects are independent of the chemical potentials of the given species. Lattice distortion defects such as anion Frenkel (a-Fr) pair defects play an important role in transporting O-related defects between different lattice sites. To obtain red persistent luminescence that matches the biological therapeutic window, it is suggested to increase the electron transition levels between high-coordinated O vacancies and related metastable a-Fr defects; a close-packed core-shell structure is required to quench low-coordinated O-related defects so as to reduce the green band luminescence. We further established a conversed chain reaction (CCR) model to interpret the energy conversion process of persistent luminescence in terms of the inter-reactions of native point defects between different charge states. It is advantageous to use the study of defect levels combined with formation energies to suggest limits to doping energy and explain photostimulated luminescence in terms of native point defects.