Lithium Substitution Endowing Cr³⁺-Doped Gallium Germanate Phosphors with Super-Broad-Band and Long Persistent Near-Infrared Luminescence

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 Light and X‐Ray Charging in Persistent Luminescence Nanocrystals for Orthogonal Afterglow Anti‐Counterfeiting

“…We attribute the new emerged TL peak at ≈410 K and the enhanced inherent TL peak at ≈324 K to the non‐equivalent substitution of Zn 2+ by Li + , which could possibly create defects and increase the amount of O 2− vacancies () for charge compensation. [ 34–36 ] The thermoluminescence peak associated with the inherent electron trap slightly shifted toward a higher temperature after lithium‐doping (324, 327, 330, and 332 K for nanocrystals with 0%, 10%, 30%, and 40% lithium doping, respectively). We also integrated the TL at 410 K peak and calculated its percentage in the total TL.…”

Competitive Cr3+ occupation in persistent phosphors toward tunable traps distribution for dynamic anti‐counterfeiting

“…The TL spectra of LZG: 0.08% Cr 3+ irradiated under a UV lamp at different times are shown in Figure 4A, and a trend of TL intensity first increasing and then decreasing with the increase of radiation time was observed. The process of filling the trap with electrons by irradiation can be thought of as a charging process; that is, with the increase of charging time, the electric quantity increases continuously until the sample is fully charged after irradiation for 14 min 32 . Later, the TL intensity decreases slightly, because when the trap is filled, the rate of electrons released into CB increases greatly.…”

“…The process of filling the trap with electrons by irradiation can be thought of as a charging process; that is, with the increase of charging time, the electric quantity increases continuously until the sample is fully charged after irradiation for 14 min. 32 Later, the TL intensity decreases slightly, because when the trap is filled, the rate of electrons released into CB increases greatly. In this case, the filling rate of electrons is less than the release rate, resulting in relatively lower carrier concentration in the trap, correspondingly reduced escape rate, and reduced TL intensity.…”

A New Near‐Infrared Long Persistent Luminescence Material with Its Outstanding Persistent Luminescence Performance and Promising Multifunctional Application Prospects

“…Of course, there are some special cases where the two situations can occur at the same time, but it means that Cr 3+ ions in the octahedron should have an intermediate field environment. [ 25 ] The specific information can be obtained by referring to the Tanabe–Sugano diagram of 3d 3 in octahedral configurations ( Figure a). [ 26 ] And the crystal field strength D q and Racha parameters B can be obtained by calculating the relative energy between the Cr 3+ levels.…”

“…In general, the presence of afterglow phenomenon is strongly related to traps, such as oxygen vacancies. [ 25,33–35 ] And the depth and number of traps have a great influence on the PersL performance. On this basis, the 3D thermoluminescence (TL) spectra of the NCGSO:0.8%Cr 3+ were tested, and the result is displayed in Figure .…”