Enhai Song

Abstract Luminescent metal halide materials with flexible crystallography/electronic structures and tunable emission have demonstrated broad application prospects in the visible light region. However, designing near‐infrared (NIR) light‐emitting metal halides remains a challenge. Here, an enlightening prototype is proposed to explore the high‐efficiency broadband NIR emission in metal halide systems by incorporating Sb 3+ into the Cs 2 ZnCl 4 matrix. Combined experimental analysis and density functional theory calculations reveal a modified self‐trapped excitons model to elaborate the NIR emission. The high photoluminescence quantum yield of 69.9% peaking at 745 nm and large full width at half maximum of 175 nm, along with excellent air/thermal stability, show the unique advantages of lead‐free metal halide Cs 2 ZnCl 4 :Sb 3+ as the NIR light source. The substitution of Cl − by Br − further enables the red‐shift of emission peak from 745 to 823 nm. The NIR light‐emitting diode device based on Cs 2 ZnCl 4 :Sb 3+ demonstrates potential as a non‐visible light source in night vision. This study puts forward an effective strategy to design the novel eco‐friendly and high‐efficiency NIR emissive materials and provides guidance for expanding the application scope of luminescent metal halides.

Abstract Doping impurity ions into semiconductor luminescent materials offers a unique pathway for inducing new emission centers and enabling photoluminescence (PL) tuning. Among various luminescence materials, doping Mn 2+ into metal halide perovskites becomes a hot topic since Mn 2+ ions demonstrate an energy transfer route from host to dopants, resulting in interesting photophysical properties. This review aims to discuss the PL properties of Mn 2+ ions in halide perovskites nanocrystals or bulk crystals with different structural dimensions and local environments (MnX 4 2– tetrahedron, MnX 6 2– octahedron, or shortest Mn─Mn distance). In this regard, the effects of Mn 2+ doping on the PL properties and their modifications are summarized. Variable ion exchange dynamics, increased emission intensity, and enhanced stability induced by Mn 2+ doping are analyzed. These results also provide beneficial insights into applications of the doped luminescent halide perovskites. Finally, the present challenges in Mn 2+ ‐doped luminescent halide perovskites are elaborated.

Following pioneering work, solution-processable Mn4+-activated fluoride pigments, such as A2BF6 (A = Na, K, Rb, Cs; A2 = Ba, Zn; B = Si, Ge, Ti, Zr, Sn), have attracted considerable attention as highly promising red phosphors for warm white light-emitting diodes (W-LEDs). To date, these fluoride pigments have been synthesized via traditional chemical routes with HF solution. However, in addition to the possible dangers of hypertoxic HF, the uncontrolled precipitation of fluorides and the extensive processing steps produce large morphological variations, resulting in a wide variation in the LED performance of the resulting devices, which hampers their prospects for practical applications. Here, we demonstrate a prototype W-LED with K3AlF6:Mn4+ as the red light component via an efficient and water-processable cation-exchange green route. The prototype already shows an efficient luminous efficacy (LE) beyond 190 lm/W, along with an excellent color rendering index (Ra = 84) and a lower correlated color temperature (CCT = 3665 K). We find that the Mn4+ ions at the distorted octahedral sites in K3AlF6:Mn4+ can produce a high photoluminescence thermal and color stability, and higher quantum efficiency (QE) (internal QE (IQE) of 88% and external QE (EQE) of 50.6%.) that are in turn responsible for the realization of a high LE by the warm W-LEDs. Our findings indicate that the water-processed K3AlF6 may be a highly suitable candidate for fabricating high-performance warm W-LEDs.

Abstract Photoluminescence originated from doped activators in the solid state materials usually faces the challenge of concentration quenching, restricting the further increase of photoluminescence intensity. Herein, a new strategy is demonstrated by the heavy doping Mn 2+ into MgAl 2 O 4 , leading to the broad‐band near‐infrared (NIR) emission peaking at ≈825 nm with a full width at half maximum of ≈125 nm, as well as high internal quantum efficiency of ≈53% upon 450 nm laser excitation. Density functional theory calculation and extend X‐ray absorption fine structure provide a understanding of Al 3+ /Mn 2+ disorder and Mn 2+ –Mn 2+ aggregation in spinel Mg 1–x Al 2 O 4 : x Mn 2+ with high Mn 2+ content, which enables the formation of superexchange coupled IV Mn 2+ – VI Mn 2+ pair. The NIR light‐emitting diodes fabricated by the 450 nm blue chip and Mg 0.50 Al 2 O 4 :0.50Mn 2+ phosphor gives a high NIR output power of ≈78.41 mW under a driven current of 120 mA, and night‐vision application as light source in the dark is demonstrated. This work opens new paths for rational design of efficient broad‐band NIR emitting phosphor, and also provides new insights into the Mn 2+ luminescence and the applications.

Abstract The development of highly efficient and thermally stable broadband near‐infrared (NIR) luminescence materials is a great challenge to advance the next‐generation smart NIR light source. Benefitting from the low phonon energy and relatively weak electron phonon coupling effect of the fluoride, K 2 NaScF 6 :Cr 3+ phosphor is designed and obtained, which demonstrates a full width at half maximum of 100 nm peaking at ≈765 nm. Upon blue light excitation, the phosphor exhibits a high quantum efficiency of 74% and its emission intensity at 150 °C can keep 89.6% of the initial value at 25 °C. An NIR output power of 159.72 mW (input electric power, 1094 mW) with a high photoelectric conversion efficiency of ≈14.60%, light‐emitting diode (LED) device is presented based on this K 2 NaScF 6 :Cr 3+ phosphor. Furthermore, applying the high‐power NIR phosphor‐converted LED device as lighting source, clear and quick veins imaging and recognition in fingers, palm, wrist, and arm of the human hand are first realized, suggesting K 2 NaScF 6 :Cr 3+ phosphor has high promise in practical applications.