Research On Luminescence And Long-persistent Luminescence Properties Of Cr³⁺/Mn²⁺ Doped ZnGa₂O₄ Systems

Long-persistent luminescent?LLP?material is a kind of special material which can continue to emit light after the optical excitation is stopped.This kind of material is mainly used in the fields of instrument clock display,safety indication and decoration,etc..In recent years,the study of near-infrared long-persistent luminescent materials has been applied to fluorescent probes and biological imaging.A large number of reports have shown that the ZnGa₂O₄ material with spinel structure can be applied to fluorescence imaging after doping Cr³⁺ ions.However,the LLP mechanism for this kind of material remains unclearly due to the neglction of some intrinsic defects.Furthermore,its emission peaks owns a poot adjustabilitiy.So we carried out in-depth research on ZnGa₂O₄ doped transition metal Cr³⁺,Mn²⁺ systems.The main research results are as follows:1,ZnGa₂O₄:Cr³⁺ phosphors were prepared by high temperature solid state method,and the prepared samples were treated in different atmospheres to obtain ones with different defect concentrations.The obtained samples were characterized by excitation fluorescence spectra,afterglow spectra,thermoluminescence spectra and AC impedance measurement.The formation energy and the electron band structure of the designed model are calculated by the first principles calculations.Results show that the oxygen vacancies?VO··?defects in the neighbor of Cr³⁺ could probably change the contents of antisite defects and result in variation of R/N2 ratio in PL and afterglow spectra.VO·· defects may also serve as the deep traps,which might agglomerate with Cr³⁺ and antisite defects to form cluster that is responsible for visible-light-stimulated LLP but with a negative effect.Finally,the charge carriers in this doing system are identified as electrons.2,The ZnGa₂O₄:Mn system was prepared by high temperature solid state method using MnCO₃ as raw material under a weakly reducing atmosphere.The luminescence spectra show that the system has a broad peak green light centered at 502 nm and a faint red light centered at 686 nm,and the afterglow spectrum shows that both emission peaks have long-persistent luminescence.The reasons for the emission of 686 nm red light are discussed,which exclude the possibility as follows: Mn²⁺-Mn²⁺ dimer and Cr³⁺ impurities.It stands a good chance that it originates from Mn²⁺.At the same time,ZnGa₂O₄:Mn system prepared by MnO₂ has the same luminescence properties as one prepared by MnCO₃.Charge compensation model explains the existence in the process of preparation of Mn⁴⁺ self-reduction phenomenon,and the self-reduction process may be the cause of this system long afterglow performance.Furthermore,ZnGa₂O₄:Mn,Cr blending system prepared by solid-state method exits dual emission peaks centered at 502 and 695 nm,respectively,in the afterglow spectra.Fluorescence spectrum and decay curves show that Mn²⁺ and Cr³⁺ may be coupled to form dimers.What's more,there exits a possibility that Mn²⁺ has the chance to transfer energy to Cr³⁺.Afterglow spectrum and the thermoluminescence spectra of the mixing system show that the oxygen vacancy has great effect on long-persistent luminescence.By adjusting the doping concentration of Cr³⁺,the relative afterglow intensity of green and red light in this system can be controlled,so as to realize the control of the afterglow color.The results will help to deepen our understanding of the transition metal doped gallium salt system,which would provide some reference for the design of new long afterglow materials.What's more,the realization of the dual color long-persistent luminescence in the ZnGa₂O₄ system provides a new possibility for the application of this kind of material.