Zhipeng Ci

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.

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

A vivid example of turning waste into treasure: persistent luminescence of Ca2Ga2(Si,Ge)O7:Pr3+,Yb3+ phosphor tailored by band gap engineering

We exhibit a vivid example of turning waste into treasure for the development of persistent luminescence (PersL) phosphor. Facing the original experimental failure in which the as-synthesized Ca2Ga2SiO7:Pr3+,Yb3+ phosphor showed very weak PersL, we did not give up but made a deep analysis. It reveals that the relatively deep depth of traps (0.72 eV) may be the key reason for the weak PersL of Ca2Ga2SiO7:Pr3+,Yb3+ phosphor. Accordingly, in order to make the depth of the traps more shallow, a band gap engineering method was applied by the partial substitution of Si4+ with Ge4+ ions. Investigation into the optical spectra and the electronic structures indicate that the band gap has been successfully reduced. Correspondingly, the depth of traps becomes shallower, and it is adjusted in an appropriate range (around 0.65 eV) when Si : Ge = 1 : 9. As a consequence, the original “waste” phosphor with very weak PersL is successfully turned into a valuable PersL phosphor: Ca2Ga2(Si0.1Ge0.9)O7:Pr3+,Yb3+, whose PersL duration time and initial PersL brightness have been increased by 74 times and 52 times, respectively, compared with the original Ca2Ga2SiO7:Pr3+,Yb3+ sample.

A thermal-sensitizing and thermochromic phosphor

Phosphors are efficient luminescent materials that are being extensively used in lighting and displays in todays world. However, the serious emission loss at high temperatures due to thermal quenching effects is still one of the most significant challenges that limit the application of phosphors. Herein, we report a unique thermal sensitizing effect of the Na2CaGe6O14:Pr3+ phosphor, in which the red emission of Pr3+ is significantly enhanced with the increase in temperature, even upto 250 °C. Moreover, the emission of the phosphor still keeps increasing over time at high temperatures. This thermally induced emission increase originates from the generation of more defect levels and more efficient energy transfer from the defects to Pr3+ at higher temperatures. This significant discovery may enlighten a new strategy to minimize or even completely eliminate the serious thermally induced emission loss of the phosphors.