No abstract

A way to improve the properties of near-infrared long persistent luminescence (NIR LPL) phosphor has been proposed, which is introducing the cation Li + which acts as both a cosolvent and a producer of additional defect. In this work, the afterglow time of Mg 2.85 Li 0.03 Ga 1.99 GeO 8 :0.01Cr 3+ lasts more than 15 h by introducing excessive Li + to Mg 3 Ga 2 GeO 8 :Cr 3+ (4 h). Moreover, the internal relationship between traps and afterglow has been comprehensively and systematically investigated by analyzing the thermoluminescence (TL) properties of Mg 3−x/2 Li x Ga 1.99 GeO 8 :0.01Cr 3+ carefully from three different aspects, such as different Li + concentrations (x = 0− 0.3), irradiation times (30 s−8 min), and afterglow decay times (30 s−10 h). The results reveals that the shallow traps preferentially act on the afterglow process to produce an intense and short luminescence, while deep traps act on the afterglow process by the tunneling effect to produce a weak and long-lasting luminescence. It is confirmed that the traps in the materials are continuously distributed, and the trap depths are calculated by using the initial rise method; the afterglow at room temperature is attributed to the traps with energy of 0.55−1.25 eV. Moreover, the motion trajectory of the carriers in the LPL decay process was further analyzed by establishing the persistent luminescence mechanism model. In addition, the material irradiated for 7 min at 0.3 Li + shows the optimum TL and afterglow properties and has a broad-band emission from 680 to 1100 nm. Therefore, the NIR LPL phosphor Mg 2.85 Li 0.03 Ga 1.99 GeO 8 :0.01Cr 3+ has good potential application prospects in the field of in vivo imaging.

Enhancing the afterglow performance is vital for the near-infrared long persistent luminescence (NIR LPL) material field. Herein, a series of Cr 3+ −Ln 3+ codoped near-infrared long p e r s i s t e n t l u m i n e s c e n c e p h o s p h o r s Mg 2.85 Li 0.3 Ga 1.99−x Ln x GeO 8 :0.01Cr 3+ (Ln = Pr, Eu, Dy, Tm, Yb, Sm) are studied to optimize their performance. Interestingly, excellent afterglow properties can be obtained even if the lanthanide ions located outside the band gap are codoped. Also, this afterglow duration of Mg 2.85 Li 0.3 Ga 1.99−x GeO 8 :0.01Cr 3+ ,xEu 3+ / Pr 3+ can be more than 24 h. We analyze the position of the lanthanide ions relative to band gap based on the establishment of the band gap energy level model. Thermoluminescence (TL) experiments demonstrate that the distribution of traps is different after doping different lanthanide ions. This is consistent with the results of electron spin resonance (ESR) spectroscopy. Our work proves that the shallow defect density has been greatly improved resulting from the strong distortion of the unit cell via doping lanthanide ions located outside the band gap and that the abundant 4f levels of the lanthanide ions located inside the band gap can complement the deeper defects in the material.

Using divalent alkaline earth metal ions as inducers, new luminescence centers were obtained by manual intervention, thus achieving great enrichment and controllable adjustment of the spectrum.