Excitation Dependent Phosphorous Property and New Model of the Structured Green Luminescence in ZnO

Abstract

The copper induced green luminescence (GL) with two sets of fine structures in ZnO crystal has been found for several decades (i.e., R. Dingle, Phys. Rev. Lett. 23, 579 (1969)), but the physical origin of the doublet still remains as an open question up to now. In this paper, we provide new insight into the mechanism of the structured GL band in terms of new experimental findings and theoretical calculations. It is found, for the first time, that the GL signal exhibits persistent afterglow for tens of minutes after the switch-off of below-band-gap excitation light but it cannot occur under above-band-gap excitation. Such a phosphorous property may be interpreted as de-trapping and feeding of electrons from a shallow trapping level via the conduction band to the Cu-related luminescence centers where the Cu3+ ion is proposed to work as the final state of the GL emission. From first-principles calculation, such a Cu3+ ion in wurtzite ZnO prefers a high spin 3d8 state with two non-degenerated half-filled orbitals due to the Jahn-Teller effect, probably leading to the double structures in photoluminescence spectrum. Therefore, this model gives a comprehensively new understanding on the mechanism of the structured GL band in ZnO.

Extinction of the zero-phonon line and the first-order phonon sideband in excitonic luminescence of ZnO at room temperature: the self-absorption effect

“…2a, both OPA-PL and TPA-PL spectra show similar spectral features at 4 K, e.g. comprising three types of principal emission lines and their LO phonon sidebands: donor-bound-exciton (DX-mLO), free-exciton (FX-mLO), and two-electron-satellite (TES-mLO) emissions with m = 0, 1, 2, 3 [18,19]. However, a noticeable difference between the 4 K OPA-and TPA-PL spectra is the relative intensity between the ZPL lines and their respective LO phonon sidebands.…”

“…For the sake of comparison, an OPA-PL spectrum measured under the usual front-detection configuration is also plotted in the figure and denoted by I 0 . The short-wavelength limit at 392 nm can be explained with a strong below-band-gap absorption due to the existence of shallow donors in ZnO [18]. As for the long- wavelength limit at about 402 nm, it can be understood in terms of almost zero absorption coefficient for emitted photons with wavelengths >400 nm.…”

Abnormal gas pressure sensitivity of the visible emission in ZnO quantum dots prepared by improved sol–gel method: the role of surface polarity

“…The difference might originate from the strong quantum size effect in QDs. 17,[32][33][34] The broad visible band, centered at 530 nm for both QDs and NWs, was suggested to be from near surface defects, such as oxygen vacancy or zinc interstice, 19,35,36 but the microstructural origin is still debatable so far. 37 Here we focus on the intensity variation of the broad visible emission with gas pressure.…”

Probing defects in ZnO by persistent phosphorescence

“…To elucidate so complicated problem of defects in ZnO, the proper choice of research-grade single crystals as the beginning sample could be a good idea 13,[16][17][18][19] . On the other hand, recent development in more elaborate hybrid density functional theory calculation is also very helpful to update the understanding of defects in ZnO [20][21][22] .…”

“…On the other hand, recent development in more elaborate hybrid density functional theory calculation is also very helpful to update the understanding of defects in ZnO [20][21][22] . In addition, the discovery and modeling of visible phosphorescence in high-quality ZnO single crystal under the below-band-gap (BBG) optical excitations may pave a new way to investigate the defects in ZnO 19,23 .…”