Efficient Near‐infrared Pyroxene Phosphor LiInGe2O6:Cr3+ for NIR Spectroscopy Application

April 2021, Journal of the American Ceramic Society.https://doi.org/10.1111/jace.17856

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Broadband near-infrared phosphors are essential to realize nondestructive analysis in food industry and biomedical areas. Efficient long-wavelength (>830 nm) phosphors are strongly desired for practical applications. Herein, we demonstrate an efficient broadband NIR phosphor LiInGe2O6:Cr3+, which exhibits a broad NIR emission peaking at ~880 nm with a full width at half maximum of 172 nm upon 460 nm excitation. The internal/external quantum efficiencies of LiInGe2O6:Cr3+ are measured to be 81.2% and 39.8%, respectively. The absorption of the phosphor matches well with commercial blue LEDs. Using the fabricated phosphor converted LED illuminating human palm, distribution of blood vessels can be clearly recognized under a NIR camera. These results indicate that LiInGe2O6:Cr3+ is a promising candidate to be used in future non-destructive biological applications.

A Broadband Near-Infrared Phosphor Ca3Y2Ge3O12:Cr3+ with Garnet Structure

Journal of Alloys and Compounds, Volume 863, 15 May 2021, 158699.https://doi.org/10.1016/j.jallcom.

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Near-infrared phosphor (NIR) integrated light-emitting diode (LED) has ideal application prospects in the fields of food inspection and medical imaging. Herein, we have synthesized a garnet-type Ca3Y2Ge3O12:Cr3+ NIR phosphor using solid state reaction method. Broadband NIR emission ranging from 700 to 1100 nm with a peak located at 800 nm indicates a weak crystal field strength for Cr3+, which occupies the six-coordinated Y3+ site. Moreover, the phosphor has satisfactory luminous intensity showing 81%/10% internal/external quantum efficiency and excellent luminescence thermal stability. Our work provides an excellent NIR phosphor choice for NIR LED devices.

Site engineering strategy toward enhanced luminescence thermostability of a Cr3+-doped broadband NIR phosphor and its application

Graphical abstract: Site engineering strategy toward enhanced luminescence thermostability of a Cr3+-doped broadband NIR phosphor and its application
Efficient broadband near-infrared (NIR) light sources are urgently needed for emerging applications in medicine, food analysis, and others. Nevertheless, the performance is limited by luminescence efficiency and thermostability in state-of-the-art broadband NIR phosphors. Here we demonstrate an effective strategy for achieving efficient and thermostable broadband NIR emission by site engineering in a SrGa12O19–LaMgGa11O19:Cr3+ system. Due to the structure symmetry promotion, the end-member SrGa12O19:Cr3+ shows excellent luminescence thermostability, i.e., higher luminescence quenching temperature and more remarkable color stability compared with LaMgGa11O19:Cr3+. At 500 K, the integrated PL intensity remains 86.5% of that at 290 K. Fine local structure, photoluminescence spectra and luminescence decay curves together support that the optically activated Cr3+ centers are reduced due to site symmetry change in SrGa12O19:Cr3+, leading to the remarkable luminescence thermostability. Finally, we have fabricated NIR pc-LEDs with commercial blue-light-emitting InGaN chips (450 nm), showing that SrGa12O19:Cr3+ has a high external quantum efficiency of 45% and has great potential in high-power and efficient pc-LED applications.

Structural Confinement for Cr3+ Activators toward Efficient Near- Infrared Phosphors with Suppressed Concentration Quenching

Trivalent chromium ion-doped near-infrared (NIR) phosphors have been widely studied due to their tunable emission wavelengths and broad applications. High Cr3+ concentration can improve absorption efficiency but generally results in low emission intensity due to the concentration quenching effect. Herein, we report a series of efficient NIR phosphors with suppressed concentration quenching, Sr9M1–x(PO4)7:xCr3+ (M = Ga, Sc, In, and Lu), showing a broadband NIR emission ranging from 700 to 1100 nm peaking at 850 nm upon the 485 nm light excitation. The emission peak position is almost independent of the type of M ion and the Cr3+ dopant content, and the type of M ion has little influence on the luminescence thermal quenching, indicating that [MO6] octahedra are rigid enough to keep octahedral volumes and average M3+–O2– distances nearly constant owing to the formation of the framework structure on Cr3+ substitution. The NIR emission intensities monotonously increase with the Cr3+ content increasing from 0 to 80% with suppressed concentration quenching, the intensity of Sr9Cr(PO4)7 still maintains 84.23% of Sr9Ga0.2(PO4)7:0.8Cr3+ phosphor, and the thermal quenching behavior is slightly dependent on x; these effects can be attributed to the suppressed energy transfer due to the structural confinement effect. The optimal sample, Sr9Ga0.2(PO4)7:0.8Cr3+, has an internal/external quantum efficiency of 66.3%/29.9%. Finally, we fabricate a NIR phosphor-conversion light-emitting diode and demonstrate its applications in nondestructive examination and medical fields.

Tuning luminescence from NIR-I to NIR-II in Cr3+-doped olivine phosphors for nondestructive analysis

Journal of Materials Chemistry C .Issue 16, 2021

Graphical abstract: Tuning luminescence from NIR-I to NIR-II in Cr3+-doped olivine phosphors for nondestructive analysis

The practical application of near-infrared (NIR) phosphors is hindered due to their limited light emitting region and narrow bandwidth. Here, we report a series of Cr3+-doped olivine phosphors, (Mg1−xLix)(Mg1−xScx)GeO4:Cr3+, with tunable luminescence from NIR-I to NIR II based on crystallographic site engineering. By using a [Li+–Sc3+] unit substituting for a [Mg2+–Mg2+] unit, the NIR luminescence can be largely tuned from 940 nm to 1110 nm, and the corresponding FWHM can be modified from 236 to ∼300 nm. The internal quantum efficiency (IQE) and external quantum efficiency (EQE) of Mg2GeO4:1% Cr3+ were measured to be 48.19% and 16.38%, respectively. The photoluminescence of the phosphors matches well with the absorption of several functional groups. By measuring the NIR absorption of different liquids illuminated by NIR light from our phosphors, qualitative and quantitative analysis can be realized. These results suggest that the super-broad NIR luminescence of (Mg1−xLix)(Mg1−xScx)GeO4:Cr3+ has potential applications as light sources for nondestructive food analysis.

 

Highly efficient near-infrared phosphor LaMgGa11O19:Cr3+

Inorg. Chem. Front., 2020,7, 1467-1473. https://doi.org/10.1039/D0QI00063A

Near-infrared (NIR) phosphor-converted light-emitting diodes (pc-LEDs) are desirable for in vivo imaging and applications for nondestructive examination in the food industry. Accordingly, it is very important to exploit highly efficient and stable broad-band NIR phosphors. Herein we report a Cr3+-activated LaMgGa11O19 phosphor via a simple solid-state reaction, showing broad-band emission centered at 770 nm with internal/external quantum efficiency of 82.6%/42.5%. There are three six-coordinated octahedral crystallographic sites in the structure for Cr3+ occupancy, and changing the Cr3+ concentration can tune the NIR emission with tunable band centers from 715 to 800 nm. This spectral red-shift is mainly ascribed to energy transfer among multiple Cr3+ sites, which is further confirmed by decay lifetime analysis. The phosphor also shows excellent luminescence thermal stability, and the photoluminescence intensity at 410 K maintains 87% of that at room temperature. Our work provides a novel broadband NIR emission phosphor with high efficiency and excellent thermal quenching resistance for the field of NIR spectroscopy.

Double perovskite Cs2AgInCl6:Cr3+: broadband and near-infrared luminescent materials

Inorg. Chem. Front., 2019,6, 3621-3628

Searching for high performance and broader applications of inorganic halide perovskites has drawn extensive attention. In this work, a Cr3+-doped halide perovskite, Cs2AgInCl6:Cr3+, which exhibits broadband near-infrared (NIR) emission is first obtained via the traditional high temperature solid-state reaction. A broad emission band ranging from 850 to 1350 nm centered at 1010 nm with a full-width at half-maximum (FWHM) of 180 nm is assigned to the spin-allowed 4T2 → 4A2 transition of octahedrally coordinated Cr3+ ions in a very weak crystal-field environment. The excitation bands centered at 353, 565 and 800 nm can be attributed to the absorption of the Cs2AgInCl6 host, the Cr3+ d–d transitions of 4A2 → 4T1 and 4A2 → 4T2, respectively. Upon 760 nm excitation, the photoluminescence quantum yield (PLQY) of Cs2AgIn0.9Cl6:0.1Cr3+ is about ∼22.03%. Cs2AgInCl6:Cr3+ phosphors with such broadband NIR emission have potential in phosphor converted light emitting diodes (pc-LEDs) which have applications in bioimaging and biomonitoring.