Valence conversion and site reconstruction in near-infrared-emitting chromium-activated garnet for simultaneous enhancement of quantum efficiency and thermal stability

Abstract

Achievement of high photoluminescence quantum efficiency and thermal stability is challenging for near-infrared (NIR)-emitting phosphors. Here, we designed a “kill two birds with one stone” strategy to simultaneously improve quantum efficiency and thermal stability of the NIR-emitting Ca3Y2-2x(ZnZr)xGe3O12:Cr garnet system by chemical unit cosubstitution, and revealed universal structure-property relationship and the luminescence optimization mechanism. The cosubstitution of [Zn2+–Zr4+] for [Y3+–Y3+] played a critical role as reductant to promote the valence transformation from Cr4+ to Cr3+, resulting from the reconstruction of octahedral sites for Cr3+. The introduction of [Zn2+–Zr4+] unit also contributed to a rigid crystal structure. These two aspects together realized the high internal quantum efficiency of 96% and excellent thermal stability of 89%@423 K. Moreover, information encryption with “burning after reading” was achieved based on different chemical resistance of the phosphors to acid. The developed NIR-emitting phosphor-converted light-emitting diode demonstrated promising applications in bio-tissue imaging and night vision. This work provides a new perspective for developing high-performance NIR-emitting phosphor materials.

Blueshift and Photoluminescence Enhancement in Broadband Near‐Infrared Emitting Phosphor NaSr2(Al/Ga)Ge5O14: Cr3+ Dependence on the Sc/In Substitution

“…In Figure 2d, three distinct absorption peaks were detected, corresponding to the spinallowed transitions of Cr 3+ ions ( 4 A 2 to 4 T 1 ( 4 P), 4 T 1 ( 4 F), and 4 T 2 ( 4 F)); the absorption band in the 800-1200 nm range from the Cr 4+ ion was absent. [32,33] Furthermore, because Cr 3+ ions have a binding energy of 585.9 eV (Figure 2e), the NIR luminescence is unlikely to originate from Cr 4+ ions. [34,35] Note that the absorption peak intensities of NSAGO: 0.07Cr 3+ and NSGGO: 0.07Cr 3+ at 435 and 615 nm in the DR spectra are different from those of NSSGO: 0.07Cr 3+ and NSIGO: 0.07Cr 3+ .…”

Cation Occupation Engineering Realizes Valence Modulation of Manganese-Activated ZnGa2O4

“…On the other hand, the gradually introduced Mg 2+ causes uneven crystal field around Mn 4+ , which facilitates the variation of crystal field strength. 28 Meanwhile, the PLQYs of ZGO:0.001Mn and Mg-ZGO samples are depicted in Figure S10d−f. The green and red emission PLQYs of ZGO: 0.001Mn are 77.61 and 16.60%, respectively.…”

“…The first reason is the enhancement of the interaction between Mn 4+ ions due to the increase of Mn 4+ concentration. On the other hand, the gradually introduced Mg 2+ causes uneven crystal field around Mn 4+ , which facilitates the variation of crystal field strength . Meanwhile, the PLQYs of ZGO:0.001Mn and Mg-ZGO samples are depicted in Figure S10d–f.…”

Crystal Field-Engineered Cr3+-Doped Gd3(MgxGa5–2xGex)O12 Phosphors for Near-Infrared LEDs and X-ray Imaging Applications

“…Accordingly, the calculated value of D q / B drops gradually from 2.34 to 2.23 with x increase from 0 to 0.4 (Figure f and Table S7). It suggests that the crystal strength is progressively attenuated, thanks to the incorporation of impurity ions (Mg 2+ /Ge 4+ ), which consequently contribute to the broadening of the fwhm in the PL spectra. , …”