An Efficient Perovskite‐Like Phosphor with Peak Emission Wavelength at 850 nm for High‐Performance NIR LEDs

Abstract

700-1100 nm range to obtain more effective information in practical application such as food analysis, medical diagnostics, and agricultural science. [5][6][7][8] On the other hand, integrating the NIR spectroscopy into mobile phones or wearable devices are emerging demand that call for NIR light source with small size. [9,10] The traditional tungsten-halogen lamps or supercontinuum lasers cannot meet these new applications because of their large size, short lifetime, and poor efficiency. [11,12] NIR light emitting diodes (LEDs) show the advantages of small size, but their emission bandwidth is less than 50 nm, which is too narrow. [13,14] In this context, phosphor-converted LEDs (pc-LEDs) with broad NIR emission were recently proposed, where one or more kinds of NIR phosphors were coated on a blue LED chip. The broad and tunable emission band as well as the small size of such NIR pc-LEDs make them an excellent alternative light source for miniature NIR spectroscopy applications.The NIR phosphor acts as a key role to convert blue light from LED chip to broadband NIR light. [15] Thus, many efforts have been made to explore NIR phosphors with broad emission band and high efficiency, such as K 3 LuSi 2 O 7 :Eu 2+ (740 nm), [16] CaS:Eu 2+ ,Tb 3+ (810 nm) [17] and Lu 2 BaAl 4 SiO 12 :Ce 3+ ,Mn 2+ (770 nm). [18] The main drawbacks of that Eu 2+ /Ce 3+ activated phosphor are their relatively short emission wavelength (<850 nm), low internal quantum efficiency (IQE), and poor thermal stability. Thus, Cr 3+ -activated NIR phosphors draw more attention for their broad emission bandwidth and high efficiency. [19,20] For example, Song et al. reported K 2 NaScF 6 :Cr 3+ NIR phosphor with an emission band peaking at 765 nm and IQE of 74%. [21] Zheng and co-workers designed Y 2 CaAl 4 SiO 12 :Cr 3+ translucent ceramics by cation co-substitution of Ca 2+ -Si 4+ for Y 3+ -Al 3+ and achieved high IQE (90.1%) and external QE (EQE) (59.5%). [22] Highly efficient NIR emissions have also been reported in other phosphors such as Ca 2 LuHf 2 Al 3 O 12 :Cr 3+ (775 nm), [4] La 2 MgZrO 6 :Cr 3+ (825 nm), [10] Ga 2 O 3 :Cr 3+ (740 nm), [23] GdAl 3 (BO 3 ) 4 :Cr 3+ (733 nm), [24] LaMgGa 11 O 19 :Cr 3+ (770 nm) [25] and so on. Though the above NIR phosphors have high IQE and excellent thermal stability, they also suffer from deficient emission in 850-1100 nm, which limits their practical applications. Some NIR phosphors with longer wavelength emission (>850 nm), such as La 3 Ga 5 GeO 14 :Cr 3+ (920 nm), [26] ZnTa 2 O 6 :Cr 3+ (935 nm), [27] and LiIn 2 SbO 6 :Cr 3+ (965 nm), [28] were reported, but their IQEs are Near-infrared (NIR) phosphor-converted light-emitting diodes (pc-LEDs) are an emerging light source demanded for the miniaturization of NIR spectroscopy. However, the photoelectric efficiency and spectral properties of NIR pc-LEDs are still very limited due to a lack of efficient broadband NIR phosphors with peak emission wavelength >850 nm. Here, a novel Cr 3+ -activated perovskite-like Mg 4 Ta 2 O 9 phosphor is reported, which exhib...

Broadband short-wave infrared Mg4Nb2O9:Cr3+,Li+ phosphor for nondestructive safety detection and biomedical imaging

“…S8, ESI †). These observations are well consistent with the reports by Tang et al and Wang et al 36,37 However, it should be noted that the gradual increase of Cr 3+ concentration in our experiments did not induce an obvious red-shift of NIR PL peak as well as increased FWHM values (Fig. S7b, ESI †).…”

“…S2, ESI † see more discussion on the cation site occupation in ref. [32][33][34][35][36][37][38][39][40]. In chemical crystallography, the hexagonal corundum-type Mg 4 Ta 2 O 9 and Mg 4 Nb 2 O 9 can be generalized into a typical formula A 4 M 2 O 9 , where A = Mg 2+ , Mn 2+ , Fe 2+ , Co 2+ , and M = Nb 5+ , Ta 5+ .…”

“…The signal at g = 3.01 is attributed to the isolated Cr 3+ ions, and g = 1.87 signal stands for the exchange coupled Cr 3+ -Cr 3+ pairs. 36 Thus, after adding Li 2 CO 3 agent during synthesis, Li + charge compensation does work well to reduce the vacancy defects, maintain charge balance, and promote the formation of more isolated Cr 3+ ions, thereby significantly enhancing the NIR PL intensity of the Mg 4 Nb 2 O 9 :3%Cr 3+ sample. These results additionally validate the above-stated optimization effects induced by the Nb 5+ substitution, excess Li 2 CO 3 addition, as well as crystal field perturbation for enhanced absorption and luminescence.…”

“…Most recently, Tang et [36][37][38] which strongly absorbs blue B460 nm photons, generates broadband 700-1200 nm emission and FWHM up to 188 nm, and achieves a record external QE B61.3%. In practice, our group earlier in 2022 also studied the NIR emissive properties of Mg 4 Ta 2 O 9 :Cr 3+ and systematically optimized the Mg 4 Ta 2 O 9 -based Cr 3+ NIR phosphors by site engineering/cation (co-)substitution for superior performance.…”

Achieving High Quantum Efficiency Broadband NIR Mg4Ta2O9:Cr3+ Phosphor Through Lithium‐Ion Compensation

“…In addition, MgO 6 and TaO 6 octahedra are connected with adjacent octahedra in the manner of sharing face or sharing edge. [14] Although there are two crystallographically independent Mg sites, the crystal field environment between them is similar and the difference is much smaller than that of Ta sites. Similar luminescence properties of Cr 3+ occupying both Mg sites are predictable due to the extremely similar crystal field environment.…”