Tetracoordinate Fe³⁺ Activated Li₂ZnAO₄ (A = Si, Ge) Near-Infrared Luminescent Phosphors

Abstract

Fe 3+ -doped near-infrared (NIR) phosphors have received a lot of interest because they are nontoxic, inexpensive, and ecologically benign. In this work, Fe 3+ -activated Li 2 ZnAO 4 (A = Si, Ge) phosphors were synthesized by solid-phase reactions, in which Fe 3+ entered the Zn 2+ tetrahedral site. When excited by 300 nm UV light, broad NIR emission bands at 750 nm (Li 2 ZnSiO 4 : Fe 3+ ) and 777 nm (Li 2 ZnGeO 4 : Fe 3+ ) were observed, with internal quantum efficiencies (IQE) of 62.70% (Li 2 ZnSiO 4 : Fe 3+ ) and 30.57% (Li 2 ZnGeO 4 : Fe 3+ ). The thermal stability was increased from 35.43 to 49.79% at 373 K via cationic regulation. The combination of activation energy, electron−phonon coupling, and Debye temperature explained the improved thermal stability of Li 2 ZnGeO 4 : Fe 3+ phosphor. Besides, the as-synthesized phosphor demonstrated sensitive and selective Cu 2+ ion detection.

Near‐unity quantum efficiency wavelength‐tunable NIR phosphors (Sr2−yCay)Sc1−xSbO6: xFe3+ with excellent thermal stability

“…Thermal stability is an important index for evaluating NIR phosphor used in pc‐LED 19,20 . We thus conduct temperature‐dependent PL spectra of S 1‐ y Ca y SS:1%Fe 3+ ( y = 0 and 2) in the temperature range from 298 to 473 K. When y = 0, NIR emission intensity of SSS:1%Fe 3+ decreases gradually under excitation at 300 nm with temperature increases and the integrated PL intensity decreased to 70.6% at 423 K of the initial intensity at 298 K. The performance of S 1− y Ca y SS:1%Fe 3+ ( y = 0 and 2) surpass that of most Fe 3+ ‐activated phosphors such as Li 2 ZnSiO 4 :Fe 3+ (35.3%@373K), 21 CaLaMgSbO 6 :Fe 3+ (42%@373K), 7 and Ca 2 InSbO 6 :Fe 3+ (36%@398K) 1 (Table 1). At y = 2, the emission loss of CSS:1%Fe 3+ phosphor at 423 K is ∼23%, which is lower than that (∼30%) of pristine SSS:1%Fe 3+ phosphor (Figure 5A and B).…”

Achieving Broadband NIR Emission in Fe3+‐Activated ALaBB′O6 (A = Ba, Sr, Ca; B–B′ = Li–Te, Mg–Sb) Phosphors via Multi‐Site Ionic Co‐Substitutions

“…While some Fe 3+ -activated phosphors produce NIR emission, however, most have spinel hosts with only one site for Fe 3+ . [15,16] In spinel structure, the forbidden d-d transition of Fe 3+ results in low quantum yield and hinders emission beyond 800 nm. Lin and co-workers [17] tried to dope Fe 3+ into double perovskite, and adjusted NIR emission by changing the matrix composition, achieving a long-wavelength emission of 949 nm in Ca 2 InSbO 6 : Fe 3+ .…”