Tuning Spectral And Duration Properties Of Persistent Luminescence Phosphors

1.An excellent persistent luminescence(PersL)phosphor NaCa2GeO4F: Mn2+,Yb3+ has been synthesized by traditional solid-state reaction.By controlling the occupation sites of Mn2+ emitters,the PersL color of this phosphor can be optionally tuned in the red to green-yellow region,and the maximum spectral shift is more than 50 nm.Significantly,the red PersL can be measured for approximately 13 and 3 h(0.32 mcd/m2)and can be observed for more than 20 and 5 h with dark-adapted vision after exposure to ultraviolet irradiation and artificial sunlight,respectively.The crystal/electronic structure and photoluminescence/PersL properties of this phosphor have been investigated in detail.A series of the excitation temperaturedependent thermoluminescence experiments and the initial rising method have been conducted to study the trap properties of this phosphor.It reveals the reasons for the variation of PersL color,excellent red PersL,and degradation of green-yellow PersL.According to the results,the as-prepared NaCa2GeO4F:Mn2+,Yb3+ can be considered as an excellent red PersL phosphor,and it also has potential for application in optical storage.2.We combine nonequivalent substitution and charge-induced emitter-migration approaches and design an efficient method to optionally tune the spectral and duration properties of NaCa2GeO4F:Mn2+ phosphor.A series of representative codopants have been investigated in detail and classified into two categories: RA(RA = Li+,Al3+,N3-,Ga3+,B3+)and RB(RB = Mg2+,F-,Bi3+,Zn2+,Cd2+,Sc3+,Tm3+).Results reveal that the nonequivalent substitution of RA codopants would induce foreign negative defects and stabilize Mn2+ emitters at octahedral Na+/Ca2+ sites for red emission.In constrast,the RB codopants would generate foreign positive defects and make Mn2+ emitters migrate to tetrahedral Ge4+ sites for green-yellow emission.At the same time,the RA codopants are in favor of the generation of intrinsic positive traps with shallow trap depth and thus efficiently improve the duration properties of phosphors.On the basis of the experimental results,a possible nonequivalent substitution and charge-induced emitter-migration model has been proposed,and we can optionally tune the spectral(568 ? 627 nm)and the duration(minutes to more than 6 h)properties according to this model?3.Spectroscopic data in our investigation,combined with those in references,are used to construct an energy diagram of the typical Lu3Al2Ga3O12:Ln2+/Ln3+ phosphors.Based on the diagram,the persistent luminescence properties of Lu3Al2Ga3O12: Ln2+/Ln3+(Ln = La–Yb)phosphors are theoretically predicted.We have shown that the position of the 4f ground level of Ln2+ in the band gap can estimate the ability of Ln3+ codopants as foreign electron traps,and it is confirmed by our experimental results of the typical Lu3Al2Ga3O12:Tb3+,Ln3+ samples.Finally,the critical roles of the Yb3+ codopants as efficient foreign traps in the typical Lu3Al2Ga3O12:Tb3+ phosphor is revealed.The requirements for efficient foreign traps and the fundamental persistent luminescence mechanism of this phosphor are systematically summarized.4.A green-yellow emitting Pers L phosphor of Ce3+ doped Lu3Al5O12 was synthesized.Lu3Al5O12:Ce3+ showed an strong absorption band ranging from 380 to 480 nm.Under 450 nm excitation,all samples gave bright green-yellow emission peaked at 535 nm.1.1% concentration shown the optimal persistent luminescence behavior.Under sufficient 254 nm excitation,its afterglow can last for up to 12 hours.In order to further study,we use thermoluminescence to research trap information.There are 2 kinds of traps in Ce3+ codoped samples.They were due to intrinsic defects in this host.