Yuhua Wang

How to induce highly efficient long-lasting phosphorescence in a lamp with a commercial phosphor: a facile method and fundamental mechanisms

We successfully tailor the properties of a well-known commercial lamp with the Zn2SiO4:Mn2+ phosphor as a novel, highly efficient, long-lasting green phosphor by using the co-doping method. The long-lasting phosphorescence (LLP) of the optimal Zn2SiO4:Mn2+,Yb3+ sample can be recorded for approximately 30 h (0.32 mcd m−2) and is visible for even more than 60 h in the dark by using dark-adapted vision. This exciting result is sufficiently encouraging for the initiation of a more thorough investigation. Several classical methods of investigation including decay curves, thermoluminescence, fading experiments, multi-peak fitting based on general-order kinetics, and first-principles calculations are used in this study to examine the LLP properties, the effects of such co-dopants and the nature of traps in detail. The important retrapping and tunneling effects, combined with a kinetics investigation, are discussed. A modified law concerning the influences of co-dopants on the traps around the Mn2+(3d5, d → d type) centers and the LLP properties are summarized. Finally, the LLP mechanism of the Zn2SiO4:Mn2+,Yb3+ phosphor is proposed.

Photoluminescence properties of color-tunable KLaSiO4:Ce3+,Mn2+ phosphors

Abstract A series of color-tunable KLaSiO 4 :Ce 3+ ,Mn 2+ phosphors were successfully prepared and the luminescent properties were investigated. Upon excitation at 290 nm, the emission spectra of KLaSiO 4 :Ce 3+ ,Mn 2+ phosphors included a blue emission band and a red emission band. Increasing the doping concentration of Mn 2+ ions, the red emission was strengthened considerably, and the blue emission of Ce 3+ was reduced, owing to the efficient energy transfer. The composition optimized KLa 0.96 SiO 4 :0.02Ce 3+ ,0.02Mn 2+ sample exhibited the white light emission brightly with the chromaticity coordinates of (0.331, 0.337). Therefore, KLaSiO 4 :Ce 3+ , Mn 2+ could be used as a white phosphor candidate for white light-emitting diodes devices.

Theoretical method to select appropriate codopants as efficient foreign electron traps for Lu 3 Al 2 Ga 3 O 12 :Tb 3+ /Ln 3+ persistent phosphor

Spectroscopic data in our investigation, combined with those in references, are used to construct an energy diagram of the typical Lu3Al2Ga3O12:Ln(2+)/Ln(3+) phosphors. Based on the diagram, the persistent luminescence properties of Lu3Al2Ga3O12:Ln(2+)/Ln(3+) (Ln = La-Yb) phosphors are theoretically predicted. We have shown that the position of the 4f ground level of Ln(2+) in the band gap can estimate the ability of Ln(3+) codopants as foreign electron traps, and it is confirmed by our experimental results of the typical Lu3Al2Ga3O12:Tb3+, Ln(3+) 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

An outlook of rare-earth activated persistent luminescence mechanisms

Abstract By studying energy transfer and persistent energy transfer properties in Eu, Mn co-doped calcium aluminate CaAl2O4, it was found that traditional persistent luminescence mechanisms had difficulty in explaining persistent energy transfer property between Eu2+ and Mn2+ ions. Based on this question, a mechanism was suggested in which vibrational energy levels were considered as a Morse potential, and trap centers were distinguished into barriers and wells. Then, this phenomenon was explained by allowing energy transfer and persistent energy transfer could have different preference to different vibrational energy levels. Properties of trap centers were also discussed by using the concept of Madelung energy.

A novel un-doped long lasting phosphorescence phosphor: SrZrSi2O7

A novel phosphor of un-doped SrZrSi2O7 material with blue long lasting phosphorescence which could be recorded for about 5400 s (0.32 mcd/m(2)) was developed. It revealed that both the emission centers and traps levels were related to the oxygen-deficient defects which were induced in reducing atmosphere. The filling and fading experiments indicated that the traps levels in SrZrSi2O7 were continuous in distribution. The influence of shallow traps on deep traps was investigated and the important role of the bridge effect was revealed. The un-doped SrZrSi2O7 material obtained in reducing atmosphere showed potential application as a cheap blue long lasting phosphorescence phosphor.