Enhanced up-conversion persistent luminescence of Zn2GeO4:Mn phosphors by non-equivalent doping and sensitization of up-conversion nanocrystals

Up-conversion persistent luminescence (UCPL) nanoparticles have captured tremendous attention due to their unique optical operating performance such as the absence of auto-fluorescence and the charging capacity of near-infrared (NIR) light. However, the weak afterglow intensity as well as low duration limits their practical applications including multimode anti-counterfeiting and biological imaging, etc. Herein, typical green persistent luminescence (PersL) and photo-stimulated luminescence (PSL) of Zn 2 GeO 4 :Mn 2+ phosphors were enhanced via non-equivalent Li + co-doping, in which the preferred site selection of Mn 2+ and Li  +  have been verified by using the first-principles theory. The possible luminescent enhancement mechanisms were proposed based on improving the oxygen vacancy density and promoting the formation of Mn 4+ defect energy level in bandgap structure by non-equivalent doping of Li + . Interestingly, UCPL of Zn 2 GeO 4 :Mn 2+ ,Li  +  can be achieved after charging of Vis to NIR light. It is worth noting that this UCPL can be further enhanced by the sensitization of NaYF 4 :Yb,Tm nanoparticles via simply mixing Zn 2 GeO 4 :Mn 2+ ,Li + and NaYF 4 :Yb,Tm under 980 laser stimulation. As a result, Zn 2 GeO 4 :Mn 2+ ,Li + phosphor exhibits the enhanced quintuple-mode luminescence including photoluminescence , PersL, PSL, photo-stimulated persistent luminescence and UCPL. In particular, the achieved NIR rechargeable UCPL hybrid phosphors exhibit enormous potential for higher order anti-counterfeiting and rewriteable data encryption and decryption applications.