Enhanced Thermal Stability and Energy Transfer by Crystal‐Field Engineering in a Garnet Phosphor for Thermometry and NIR‐LED

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...

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confidence: 99%

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

Tang

Xiao

et al. 2022

Advanced Optical Materials

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“…The small residual factors (R p = 3.58%, R wp = 4.67%) imply that the refinement results are acceptable and CLAS crystallizes in the same cubic structure with space group Ia-3d as Y 3 Al 5 O 12 . [7] The refined crystal structure produced a simulated XRD pattern, which could be used as a standard card for CLAS. The XRD patterns of all the as-prepared…”

Section: Crystal Structurementioning

confidence: 99%

“…[6] For example, the emission of Ca 1−x Sr x Lu 2 Al 4 SiO 12 :Cr 3+ becomes sharper and sharper when Ca 2+ is substituted by Sr 2+ . [7] In the case of Ga 2−x Sc x O 3 :Cr 3+ , the emission intensity originating from the 2 E→ 4 A 2 spin-forbidden transition is strong at x = 0 and gradually decreases with increasing x value, i.e., decreasing local crystal field, whereas at higher Sc 3+ content, only the emission originating from the 4 T 2 → 4 A 2 spin-allowed transition is detectable. [8] However, most Cr 3+ -activated NIR phosphors exhibit poor thermal stability, limiting their potential applications.…”

Section: Introductionmentioning

confidence: 99%

Thermal Stability Improvement of Cr³⁺‐Activated Broadband Near‐Infrared Phosphors via State Population Optimization

Zhang

Wei

Milićević

et al. 2023

Advanced Optical Materials

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Technological progress has accelerated the researches into broadband near-infrared (NIR) luminescent materials as next-generation intelligent NIR light sources; however, poor thermal stability restricts the applications of NIR phosphors. Herein, new insights into Cr 3+ -activated NIR phosphors with improved thermal stability are provided. The photoluminescence intensity originating from the 4T2→4A2 broadband emission of CaLu 2 Al 4 SiO 12 :Cr 3+ (CLAS:Cr) with optimal electron occupation ( 4 T 2 / 2 E) increases up to 118% at 475 K compared with that at room temperature, which is the best for Cr 3+ -activated broadband NIR phosphor. Accordingly, new ideas for the design of thermally stable phosphors are proposed by optimizing the thermal population between 4 T 2 and 2 E states and electron migration from 2 E to 4 T 2 state. Finally, multifunctional applications of CLAS:Cr in NIR fluorescence intensity ratio thermometry, X-ray detection, NIR phosphor-converted light-emitting diodes, and bio-imaging are demonstrated.

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“…There are plenty of NIR luminescent materials, including organic dyes, quantum dots, and ion-activated phosphors. − Among them, the last one offers an unparalleled advantage in long-term stability. Cr 3+ has emerged as a star activator for its efficient and adjustable NIR emission and its excitation band matching blue LED chips. , With a d 3 electronic configuration, Cr 3+ needs to fit in octahedral crystal fields to achieve NIR emission from the 2 E g / 4 T 2g → 4 A 2g transition. , Therefore, those hosts with substitutable octahedral sites can construct NIR phosphors through doping Cr 3+ , such as LiIn 2 SbO 6 :Cr 3+ , MgSi 2 O 6 :Cr 3+ , and LiGa 5 O 8 :Cr 3+ . − Although many Cr 3+ -doped phosphors have been realized, the luminescent properties of Cr 3+ are not entirely satisfying. In particular, thermal stability, which characterizes the emission at elevated temperature, is crucial for the applications in NIR LEDs and optical thermometry, because it affects not only the emission profile but also the signal intensity. − Mn 4+ -doped phosphors with the same electronic configuration as Cr 3+ often have an anti-Stokes phonon sideband to improve their thermal stability .…”

Section: Introductionmentioning

confidence: 99%

Cr³⁺-Doped NIR Phosphor with Well-Defined Stokes/Anti-Stokes Phonon Sidebands for a Ratiometric Thermometer and Thermally Stable NIR LEDs

et al. 2023

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Near-infrared (NIR) luminescent materials have attracted enormous attention for the cutting-edge applications in optical thermometer and NIR LEDs. Herein, we report a highly efficient Cr3+-doped NIR phosphor, BaAl4Sb2O12:0.024Cr3+ (BASO:Cr3+), with 91% internal quantum efficiency. Strikingly, BASO:Cr3+ possesses rare and typical Stokes/anti-Stokes phonon sidebands. The Stokes phonon sideband decreases with increasing temperature, while the anti-Stokes one increases considerably. Consequently, this inverse change has gifted the BASO:Cr3+ with excellent thermal stability, which maintains 118% of the room temperature emission intensity at 423 K. In addition, the well-defined Stokes/anti-Stokes phonon sidebands are applied to a ratiometric thermometer with a maximum relative sensitivity factor of 3.12% K–1 at 150 K. Finally, a well-performing NIR LED is made with BASO:Cr3+, which can be used for nondestructive testing, information encryption, and night vision. Our findings not only shed light on the emission behavior of Cr3+ but also point out an avenue for thermally stable NIR phosphors and a sensitive optical thermometer.

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Enhanced Thermal Stability and Energy Transfer by Crystal‐Field Engineering in a Garnet Phosphor for Thermometry and NIR‐LED

Cited by 24 publications

References 58 publications

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

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

Thermal Stability Improvement of Cr³⁺‐Activated Broadband Near‐Infrared Phosphors via State Population Optimization

Cr³⁺-Doped NIR Phosphor with Well-Defined Stokes/Anti-Stokes Phonon Sidebands for a Ratiometric Thermometer and Thermally Stable NIR LEDs

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Enhanced Thermal Stability and Energy Transfer by Crystal‐Field Engineering in a Garnet Phosphor for Thermometry and NIR‐LED

Cited by 24 publications

References 58 publications

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

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

Thermal Stability Improvement of Cr3+‐Activated Broadband Near‐Infrared Phosphors via State Population Optimization

Cr3+-Doped NIR Phosphor with Well-Defined Stokes/Anti-Stokes Phonon Sidebands for a Ratiometric Thermometer and Thermally Stable NIR LEDs

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Thermal Stability Improvement of Cr³⁺‐Activated Broadband Near‐Infrared Phosphors via State Population Optimization

Cr³⁺-Doped NIR Phosphor with Well-Defined Stokes/Anti-Stokes Phonon Sidebands for a Ratiometric Thermometer and Thermally Stable NIR LEDs