Simultaneous Absorption and Near‐Infrared Emission Enhancement of Cr³⁺ Ions in MgGa₂O₄ Spinel Oxide via Anionic F‐Substitution

Abstract

low scattering loss, exceptional penetrability, and characteristic interactions with organic functional groups. NIR light sources thereby have widespread applications in machine vision, communications, medical diagnostics, spectroscopy, etc. [1][2][3][4][5] In particular, NIR spectroscopy is a quick, convenient, and nondestructive analytical technique in the food industry and biomedical and environmental fields, [4] where continuous broadband NIR light sources are employed as key components. The combination of efficient blue light-emitting diode (LED) chips and NIR-emitting phosphors is emerging as an ideal strategy for building novel solid-state NIR light sources. Compared with current NIR sources (e.g., incandescent bulbs, halogen lamps, and LEDs), phosphor-converted LEDs (pc-LEDs) exhibit attractive advantages of compact size, low cost, tunable broadband emission, high efficiency, and excellent durability. Furthermore, miniaturized broadband NIR pc-LEDs can be easily integrated into smartphones or wearable devices enabling new functional applications. As the principal provider of spectral output, NIR phosphors are crucial to the popularization of NIR pc-LED light sources.Lanthanide ions (Pr 3+ , Tm 3+ , Sm 3+ and Eu 2+ ) as well as transition metal ions (Mn 2+ , Ni 2+ and Cr 3+ ) can generate the NIR luminescence when incorporated into appropriate host materials. [6][7][8][9][10][11] Among them, Cr 3+ is considered as an ideal NIR emitter due to its tunable broadband NIR emission and blue-light excitation features. Numerous Cr 3+ -activated NIR phosphors have been developed, such as garnets, [12][13][14][15][16] borates, [17][18][19][20] silicates, [21,22] gallogermanates, [23][24][25][26][27][28][29][30][31] phosphates, [32][33][34] fluorides, [35][36][37] etc. Some of them exhibit high internal quantum efficiency (IQE) and good thermal stability, such as GdAl 3 (BO 3 ) 4 :Cr 3+ (λ max = 740 nm, IQE = 91%, 98% intensity retention at 150 °C), [18] Gd 3 (Sc,Al) 2 Ga 3 O 12 :Cr 3+ (λ max = 760 nm, IQE = 98.6%, 92%@150 °C), [16] and Ca 3 Sc 2 Si 3 O 12 :Cr 3+ (λ max = 770 nm, IQE = 92.3%, 97.4%@150 °C). [15] However, their peak wavelengths are short (λ max < 800 nm) and considerable emissions are in the visible light region. Such spectral output would be insufficient for spectroscopic analysis because most molecular radicals have the characteristic absorption for NIR Near-infrared (NIR) phosphor-converted light-emitting diodes (pc-LEDs) are newly emerging broadband NIR light sources. However, the lack of highperformance NIR-emitting materials limits their popularization. Herein, an anionic F-substitution strategy is presented to regulate the light absorption and emission of MgGa 2 O 4 :Cr 3+ phosphors. Accordingly, absorption enhancement as well as emission redshift and broadening are achieved for F-substituted MgGa 2 O 4 :Cr 3+ (MGOF:Cr 3+ ) phosphors, simultaneously with high efficiency and excellent thermal stability. Upon blue light excitation, the MGOF:0.02Cr 3+ phosphor exhibits a broadband NIR emission (65...

Broadband Short-Wave Infrared-Emitting MgGa2O4:Cr3+, Ni2+ Phosphor with Near-Unity Internal Quantum Efficiency and High Thermal Stability for Light-Emitting Diode Applications

“…Furthermore, Figure S1 gives the high-resolution XPS spectra of the 2p level of Cr and Ni. The Cr 2p 3/2 spectrum exhibits a maximum peak at 576.2 eV, which corresponds to the binding energy of the trivalent chromium located in the [CrO 6 ] octahedron . The XPS spectra of Ni 2p 3/2 and Ni 2p 1/2 exhibit the maximum peaks located at 856.2 and 873.9 eV, respectively, accompanied by the satellite peaks located at the higher binding energy positions of 861.9 and 880.7 eV, respectively .…”

“…There exist three different excitation bands peaking at 272, 420, and 572 nm, which are assigned to the Cr 3+ 4 A 2 → 4 T 1 ( 4 P), 4 A 2 → 4 T 1 ( 4 F), and 4 A 2 → 4 T 2 ( 4 F) transitions, respectively . Under the excitation of blue light at 420 nm, the emission spectrum consists of a strong sharp line emission centered at ∼708 nm (Cr 3+ 2 E → 4 A 2 transition) and a broadband emission ranging from 800 to 1100 nm (Cr 3+ 4 T 2 → 4 A 2 transition) Figure S2 shows the infrared luminescence spectra of the MgGa 2 O 4 : x % Cr 3+ ( x = 0.5, 1, 2, and 3) phosphors under 420 nm blue light excitation.…”

“…37 Under the excitation of blue light at 420 nm, the emission spectrum consists of a strong sharp line emission centered at ∼708 nm (Cr 3+ 2 E → 4 A 2 transition) and a broadband emission ranging from 800 to 1100 nm (Cr 3+ 4 T 2 → 4 A 2 transition). 59 Figure S2 shows the infrared luminescence spectra of the MgGa 2 O 4 :x% Cr 3+ (x = 0.5, 1, 2, and 3) phosphors under 420 nm blue light excitation. The inset shows the luminescence intensities with varying doping contents of Cr 3+ ions.…”

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

“…Compared with 60.6% EQE measured by Mg 1.2 Ga 1.8 O 3.8 F 0.2 :Cr 3+ at 425 nm, the NIR light source with higher efficiency may be obtained in practical applications. [22] Different kinds of Cr 3+ -doped NIR phosphors were synthesized in pure phase according to the synthesis method reported in the literatures. As shown in Figure 3a, the luminescence properties of MT:0.03Cr 3+ , Li + and the reported Cr 3+ -doped NIR phosphors can be directly compared by the photoluminescence spectra.…”

Spectral Broadening in Cr3+-Doped Sr0.92Mg0.91Al10.1O17 NIR Phosphor Realized by Multi-crystallographic Site Occupation

“…Near-infrared light (700–1400 nm) is an electromagnetic wave that exists between visible and mid-infrared light and is greatly utilized in plant growth, night vision, medical imaging, food analysis, and so on. − In recent years, NIR pc-LED, which is recognized as a new generation of NIR light source, has garnered a lot of attention due to its high efficiency and compact size. − Cr 3+ is one of the most frequent activators of NIR phosphors. Its luminescence is greatly impacted by the crystal field with a narrow emission in a strong crystal field and a broadband one in a weak crystal field.…”