Zn₃Ga₂Ge₂O₁₀:Cr³⁺ Uniform Microspheres: Template-Free Synthesis, Tunable Bandgap/Trap Depth, and In Vivo Rechargeable Near-Infrared-Persistent Luminescence

Abstract

Near-infrared (NIR) emitting persistent phosphors of Cr3+-doped zinc gallogermanate have emerged for in vivo bioimaging with the advantage of no need for in situ excitation. However, it is challenging to synthesize well-dispersed and uniform spherical particles with high brightness, high resolution, and distinguished NIR long afterglow. In this work, Zn3Ga2Ge2O10:Cr3+ (ZGGC) monospheres were directly synthesized by a facile hydrothermal method with the assistance of citric anions (Cit3–), which emit an NIR emission at ∼696 nm and exhibit excellent NIR-persistent luminescence with rechargeability. Controlled experiments indicated that the shape evolution of the ZGGC product is significantly affected by Cit3–, solution pH, and the duration and temperature of hydrothermal reaction. Furthermore, compositional influence on the crystal structure, bandgap, trap depth, and luminescence characteristics of Zn y Ga2Ge2O10−δ:Cr3+ (y = 2.8, 3.0, 3.2) were investigated in detail, which allows us to construct an energy level diagram of the ZGGC host, Cr3+ ions, and electron traps. It was found that the bandgap and conduction-band minimum (CBM) are significantly affected by the Zn content, while the valence-band maximum (VBM) is not. The y = 3.0 sample exhibited the best persistent luminescence, owing to its deepest defects. The ZGGC-NH2 prepared through surface functionalization of ZGGC spheres showed distinguished NIR long afterglow, low toxicity, and great potential for in vitro cell imaging and in vivo bioimaging in the absence of excitation. Moreover, the persistent luminescence signal from the ZGGC-NH2 can be repeated in vivo through in situ recharge with external excitation of a red LED lamp, indicating that the ZGGC-NH2 is suitable for applications in long-term in vivo imaging.

Near infrared mechanoluminescence from Sr3Sn2O7: Nd3+for in situ biomechanical sensor and dynamic pressure mapping

“…TL technology is a useful way to investigate these ML related traps, and the related trap depths can be obtained from the Urbath's empirical formula: E T = T m /500 . We documented the TL curves of Sr 3‐ x Sn 2 O 7 : x Nd 3+ ( x = 0.05, 0.1, 0.2, 0.5, 1.0, and 2.0 mol%) in Figure A.…”

“…Interestingly, as Figure 4B denotes, the six ML intensities can be fitted into a linear equation of y = 0.30x-65. 34 where y represents the ML intensity and x is the force. A high linearity between force and ML intensity is a prerequisite for stress sensor, 1 since this emission performance will allow visualization of stress distribution with high spatial resolution.…”

Rare earth free bright and persistent white light emitting zinc gallo-germanate nanosheets: technological advancement to fibers with enhanced quantum efficiency

“…Most of the research is focused on the exploration of Zn 3 Ga 2 Ge 2 O 10 (ZGG) doped with Mn 2+ , Bi 3+ , and Cr 3+ for their PL and/or PerL properties owing to its low synthesis temperature, high stability, excellent bio-compatibility, non-toxicity, and moderate conductivity. 1,4,18,[22][23][24][25][26][27][28][29][30][31][32][33][34][35][36] However, there are very few reports on intrinsic self-activated bluish white emission in bulk/microcrystalline ZGG. 29 Although Li et al 18 have demonstrated the visible PL in ZGG nanoparticles, their emission zone lies more in the green region which lacks commercial usage for day to day activity compared to white light emitting materials.…”

“…There have been few reports lately wherein ZGGC nanoparticles have been encapsulated inside organic frameworks, synthesized as glasses, and surface functionalized. 22,36,52 Recently we used red and green emitting ZnGa 2 O 4 :Cr 3+ nanoparticles and Zn 2 GeO 4 :Mn 2+ nanorod encapsulated PVA polymer for red and green emitting fibers. 16 But we could only achieve PerL for a very short time (B500 s) in green emitting fiber and failed to achieve any red PerL.…”

Extending the luminescence properties of zinc gallogermanate via co-doping with cost-effective metals ions (Cr3+/Mg2+, Cr3+/Ca2+, and Cr3+/Sr2+)

“…(b). It is known that the Cr 3+ introduction to ZGGO host compound creates sub-levels of energy states below the conduction band which act as trapping centers for enhancing the photoluminescence properties[35,37,38]. Accordingly, the incorporation of Mg 2+ , Ca 2+ or Sr 2+ is expected to increase the number of trapping levels which may enlarge the energy transfer from Cr 3+ levels to Mg, Ca or Sr levels.…”