On the optimisation of the broadband NIR emitter LiScO2:Cr3+

Broadband near-infrared (NIR) phosphors are the critical component of phosphor converted NIR light-emitting diode (LED) light sources. However, there are still a lack of NIR phosphors with excellent external quantum efficiency (EQE) and thermal stability. Here, we report a highly efficient broadband NIR phosphor Y3Ga3MgSiO12: Cr3+. The optimized phosphor yields an internal quantum efficiency (IQE) and an EQE of 79.9 and 33.7%, respectively. The integrated emission intensity still remains at 84.4% of that at room temperature when heated to 423 K. A broadband NIR LED lamp was made by combining as-prepared phosphor and a blue InGaN LED chip, which shows an output power of 89.8 mW with a photoelectric conversion efficiency of 17.1% driven at 525 mW input power. Our research provides a promising NIR phosphor with high efficiency broadband for the NIR light source.

Effect of R+ (R = Li, Na and K) codoping on the luminescence enhancement of broadband NIR BaZrGe3O9:Cr3+ phosphors for NIR LED

Near-infrared (NIR) phosphors attract much attention as the promising applications in food composition analysis, night vision, biosensor and so on. Except for Cr3+ ions, some non-Cr3+ ions (Eu2+, Ce3+, Bi3+) recently exhibit innovative broadband NIR light in inorganic phosphors. The key issues are to optimize their photoluminescence quantum yield and reveal unclear “structure–luminescence” relationship. Herein, photoluminescence properties of non-Cr3+-doped NIR phosphors are systematically summarized. Importantly, we propose a significant influence of local crystal structure on NIR luminescence properties. These strategies contain: (1) ligand covalency, (2) strong crystal field and distorted lattice, (3) selective sites occupation and (4) mixed valences. The proposed “structure–luminescence” relationship can provide a new insight to exploit NIR phosphors and optimize current phosphors. Besides, the concept of “high-throughput density functional theory (DFT) prediction-crystal structure design-photoluminescence performances optimization” is summarized to swiftly develop targeted NIR phosphors. Subsequently, energy transfer strategies and application prospects are summarized in details. This review discusses the relationship between crystal structure and NIR light based on high-throughput calculation method. This proposed concept can offer a guidance to exploit a series of novel NIR phosphors and clarify underlying mechanism.

Cr3+-doped near-infrared (NIR) phosphors exhibit peculiar advantages in fabricating NIR phosphor-converted light-emitting diodes (NIR pc-LEDs) for machine/night vision, plant cultivation, and nondestruction detection. However, efficient NIR phosphors doped with Cr3+ usually contain noble/rare metal ions such as In, Sc, Ga, and Ge, thus making it an essential mission to develop much cheaper NIR phosphors. In this work, we report an inexpensive broadband NIR phosphor, La2MgSnO6:Cr3+ (LMS:Cr3+), that can be easily synthesized in air. LMS:Cr3+ has two distorted octahedra lattice sites for Cr3+ doping and displays a wide emission spectrum covering the range of 600–1200 nm with an emission maximum of 751 nm and a full width at half-maximum (fwhm) of 104 nm under 450 nm excitation. The broadband NIR emission originated from two distinct crystallographic sites and a medium-strength crystal field for Cr3+. LMS:Cr3+ shows an optical band gap of 3.72 eV, and its emission intensity can still maintain 68.5% at 423 K. Finally, a prototype NIR pc-LED fabricated by combining LMS:0.01Cr3+ and a blue LED is demonstrated for applications in plant cultivation, night vision, and recognition of cultural relics.

Broadband near-infrared emitting Sr3Sc4O9: Cr3+ phosphors: Luminescence properties and application in light-emitting diodes

There is strong demand for ultraefficient near-infrared (NIR) phosphors with adjustable emission properties for next-generation intelligent NIR light sources. Designing phosphors with large full-width at half-maximum (FWHM) variations is challenging. In this study, novel near-ultraviolet light-emitting diode(LED)-excited NIR phosphors, MgAlGa0.7 B0.3 O4 :Cr3+ (MAGBO:Cr3+ ), with three emission centers achieve ultra-narrowband (FWHM = 29nm) to ultra-broadband (FWHM = 260nm) emission with increasing Cr3+ concentration. Gaussian fitting and decay time analysis reveal the alteration in the FWHM, which is attributed to the energy transfer occurring between the three emission centers. The distinct thermal quenching behaviors of the three emission centers are revealed through the temperature-dependent decay times. The ultra-broadband NIR phosphor MAGBO:0.05Cr3+ exhibits high thermal stability (85%, 425 K) and exceptional external quantum efficiency of 68.5%. An NIR phosphor-converted LED (pc-LED) is fabricated using MAGBO:0.05Cr3+ phosphor, exhibiting a remarkable NIR output power of 136mW at 600mA in ultra-broadband NIR pc-LEDs. This study describes the preparation of highly efficient phosphors and provides a further understanding of the tunable FWHM, which is vital for high-performance NIR phosphors with versatile applications.

This study presents the development of Cr2O3 – doped glass-ceramic phosphors with the possibility of obtaining Cr³⁺/Cr⁴⁺ for broadband near – infrared (NIR) emission, targeting for potential applications in NIR phosphor – converted LEDs (pc – LEDs). Optimization of Cr₂O₃ doping and annealing conditions of glass-ceramic, we achieved emission in the range of NIR – I (700 – 950 nm) and NIR – II (1000 – 1700 nm) biological windows. Based on the luminescence measurements performed, in the glass sample, emission bands attributed to Cr³⁺ in an octahedral environment were observed with strong emission at 955 nm (corresponding to the transition 4T2 → 4A2), while emission of annealed glass – ceramics suggested the appearance of Cr⁴⁺ with a peak at 1250 nm (3T2 → 3A2). Full Text: PDF References V. Rajendran, T. Lesniewski, S. Mahlik, M. Grinberg, G. Leniec, et al., "Ultra-Broadband Phosphors Converted Near-Infrared Light Emitting Diode with Efficient Radiant Power for Spectroscopy Applications", ACS Photonics 6, 3215 (2019). CrossRef K. Sadowska, T. Ragiń, M. Kochanowicz, P. Miluski, J. Dorosz, et al., "Analysis of Excitation Energy Transfer in LaPO4 Nanophosphors Co-Doped with Eu3+/Nd3+ and Eu3+/Nd3+/Yb3+ Ions", Materials 16, 1588 (2023). CrossRef X. Wang, Z. Wang, M. Zheng, J. Cui, Y. Yao, et al., "A dual-excited and dual near-infrared emission phosphor Mg14Ge5O24:Cr3+,Cr4+ with a super broad band for biological detection", Dalton Trans. 50, 311 (2021). CrossRef M.-H. Fang, P.-Y. Huang, Z. Bao, N. Majewska, T. Leśniewski, et al., "Penetrating Biological Tissue Using Light-Emitting Diodes with a Highly Efficient Near-Infrared ScBO3:Cr3+ Phosphor", Chem. Mater. 32, 2166 (2020). CrossRef T. Gao, Y. Liu, R. Liu, W. Zhuang, "Research Progress and Development of Near-Infrared Phosphors", Materials 16, 3145 (2023). CrossRef T. Narendrudu, S. Suresh, G. Chinna Ram, N. Veeraiah, D. Krishna Rao, "Spectroscopic and structural properties of Cr3+ ions in lead niobium germanosilicate glasses", J. Lumin. 183, 17 (2017). CrossRef W.A. Pisarski, J. Pisarska, G. Dominiak-Dzik, W. Ryba-Romanowski, "Transition metal (Cr3+) and rare earth (Eu3+, Dy3+) ions used as a spectroscopic probe in compositional-dependent lead borate glasses", J. Alloys Compd. 484, 45 (2009). CrossRef Z. Xiao, S. Qin, X. Guo, X. Xu, W. Anaerguli, et al., "Efficient and broadband near-infrared emission of Cr<>sup>3+-doped glass-ceramics for near-infrared light sources applications", J. Lumin. 247, 118907 (2022). CrossRef

Near-infrared (NIR) phosphor conversion light-emitting diodes (pc-LEDs) have great application potential as NIR light sources in many fields such as food analysis, night vision illumination, and bioimaging for noninvasive medical diagnosis. In general, phosphors synthesized by a high-temperature solid-phase method have large particle sizes and have to be processed to fine powders by a grinding process, which may introduce surface defects and lower the luminous efficiency. Here, we report a sol-gel sintering method with ammonium nitrate and citric acid as the sacrificing agents to synthesize high purity, nanosized (less than 50 nm) Zr4+/Ni2+ codoped MgAl2O4 spinel NIR phosphors, in which MgAl2O4 spinel is the matrix, Ni2+ is the luminous center, and Zr4+ acts as the charge compensator. We systematically characterized the crystal structures and NIR luminescence properties of the Ni2+-doped MgAl2O4 and the Zr4+/Ni2+ codoped MgAl2O4. Under 390 nm light excitation, the emission spectrum of the Ni2+-doped MgAl2O4 phosphor covers 900-1600 nm, the half-peak width is 251 nm, and the peak position is located at 1230 nm. We demonstrated that by incorporating small amounts of Zr4+ as the charge compensator, the NIR emission intensity of the Zr4+/Ni2+ codoped MgAl2O4 nanosized phosphor was doubled over that of the Ni2+-doped MgAl2O4 phosphor. The optimal content of the charge compensator was 2 mol %. More importantly, the inclusion of Zr4+ led to a NIR phosphor with improved thermal stability in luminous properties, and the luminous intensity measured at 100 °C was 33.83% of that measured at room temperature (20 °C). This study demonstrates that NIR phosphor nanomaterials with high-purity and enhanced optical properties can be designed and synthesized through the charge compensation strategy by a sol-gel sintering method.

Multifunctional optical sensing applications of luminescent ions doped perovskite structured LaGaO3 phosphors in near-infrared spectroscopy

Broadband near‐infrared (NIR) phosphor‐converted light‐emitting diodes (pc‐LEDs) have many prospective applications in areas related to food inspection, health management, plant growth, and night vision, because NIR phosphors are critical components of the corresponding devices. Given the wide‐ranging applicability of the material, this study is designed to comprehensively evaluate a series of novel NIR phosphors: BaMgGaxAl10–xO17:Cr3+ (x = 0, 1, 2, 3). The ultra‐low‐temperature (4 K) fluorescence spectroscopy and decay curve results confirm that Cr3+ occupies the four lattice sites of Al3+ in the matrix. Additionally, the introduction of Ga3+ increases the full‐width at half‐maximum (FWHM) of the NIR spectrum from 100 to 300 nm without affecting the fluorescence efficiency; it also considerably increases spectral coverage. An experiment to evaluate the applicability of the novel NIR phosphors reveals that the sunlight‐converting film prepared by applying the material combination of BaMgGa3Al7O17:0.02Cr3+ is able to effectively promote the growth of Chlorella. In addition, the NIR pc‐LED with a BaMgGa3Al7O17:0.2Cr3+ basis and 395‐nm LED chip has been proven to be an excellent candidate for applications in NIR spectral detection and night‐vision technology.

To overcome the problem of severe thermal quenching (TQ) of near-infrared (NIR) phosphors, the NIR phosphor with antithermal quenching performance is urgently needed. In this work, a negative thermal expansion (NTE) material Yb2-2xCr2xW3O12 was prepared. Through a comprehensive analysis involving in situ X-ray diffractometer (XRD), thermogravimetry (TG), and Rietveld refinement, it was concluded that, at room temperature, the sample adopts a trihydrate orthorhombic structure (Yb2W3O12·3H2O) and does not exhibit negative thermal expansion (NTE) behavior. However, after dehydration at 373 K, anhydrous orthorhombic Yb2W3O12 (space group Pbcn), which exhibits obvious NTE properties, was obtained. The underlying mechanism is that when water molecules enter the crystal and occupy vacancies, the Yb-O-W bonds bend, restricting the transverse thermal vibrations of the Yb-O-W bonds. The characteristic emission of Yb3+ within the range of 800-1300 nm was observed under 468 nm blue light irradiation due to the efficient energy transfer from Cr3+ → Yb3+. Remarkably, the prepared NIR phosphor has antithermal quenching performance, and at 398 K, the intensity of the strongest emission can maintain 1.89 times that of the room temperature, surpassing most NIR phosphors. The antithermal quenching phenomenon is attributed to cell contraction, which reduces the distance between the sensitizer and activator, thereby enhancing the energy transfer efficiency and increasing the luminous intensity. The combination of 460 nm excitable strong NIR emission and antithermal quenching suggests potential application in biomedical imaging and infrared night vision technologies. The NIR pc-LED device, prepared by coating the Yb1.94Cr0.06W3O12 phosphor on a commercial 460 nm chip, demonstrated a high optoelectronic efficiency and high output power, making it well-suited for night vision applications. Furthermore, the efficient NIR-I/II emission from Yb1.94Cr0.06W3O12 was proved to be highly effective for compositional analysis. This study offers valuable insights for designing NIR phosphors with excellent thermal quenching resistance.

In recent years, near-infrared (NIR) phosphors have attracted great research interest due to their unique physical properties and broad application prospects. However, obtaining NIR phosphors with both high quantum efficiency and excellent thermal stability remains a great challenge. In this study, novel NIR Ca3Mg2ZrGe3O12:Cr3+ phosphors were successfully prepared using a high-temperature solid-phase method, and the structure and luminescent properties of the material were systematically investigated. Ca3Mg2ZrGe3O12:0.01Cr3+ emits NIR light in the range of 600 to 900 nm with a peak at 758 nm and a half-height width of 89 nm under the excitation of 457 nm blue light. NIR luminescence shows considerable quantum efficiency, and the internal quantum efficiency of the optimized sample is up to 68.7%. Remarkably, the Ca3Mg2ZrGe3O12:0.01Cr3+ phosphor exhibits a near-zero thermal quenching behavior, and the luminescence intensity of the sample at 250 °C maintains 92% of its intensity at room temperature. The mechanism of high thermal stability has been elucidated by calculating the Huang Kun factor and activation energy. Finally, NIR pc-LED devices prepared from Ca3Mg2ZrGe3O12:0.01Cr3+ phosphor with commercial blue LED chips have good performance, proving that this Ca3Mg2ZrGe3O12:0.01Cr3+ NIR phosphor has potential applications in night vision and biomedical imaging.

LiGaP2O7:Cr3+, Yb3+ phosphors for broadband NIR LEDs toward multiple applications

The rapid development of near‐infrared (NIR) spectroscopy urgently requires the exploration of NIR‐emitting phosphors with excellent luminescence properties. Herein, GaTaO4:Cr3+,Yb3+ NIR phosphor with excellent luminescence properties is reported, which exhibits ultra‐broadband NIR emission with a full width at half maximum of 300 nm, good thermal stability of 90%@423 K, and most remarkably, high internal quantum efficiency of 95.5% and external quantum efficiency of 44.79%. Such outstanding luminescence properties mainly give the credit to the unique sandwiched structure of GaTaO4:Cr3+,Yb3+, in which layers of Yb3+ ions (activator) are sandwiched between layers of Cr3+ ions (sensitizer), and hence many stable and compact Cr–Yb pairs are formed, so that the energy can be rapidly transferred from Cr3+ to Yb3+, effectively activating the characteristic f–f transition of Yb3+ that is very stable and almost independent of the temperature, and at the same time, the non‐radiative transition of Cr3+ ions can be suppressed to a certain degree. The NIR phosphor‐converted light‐emitting diodes (pc‐LEDs) are fabricated by combining GaTaO4:Cr3+,Yb3+ with blue LED chips, and the application potential is fully demonstrated by non‐destructive food detection, night vision, and vein display. The results provide novel prospects for the design of NIR‐emitting materials with desirable luminescent properties.

Broadband near-infrared (NIR) phosphors are crucial components of NIR phosphor-converted light-emitting diode (pc-LED) sources for various smart spectroscopy applications. However, developing an efficient, tunable, and inexpensive broadband NIR phosphor with sufficient spectral coverage remains a great challenge. In this work, a cubic phosphate K2AlTi(PO4)3 with highly structural rigidity was chosen as host material for Cr3+ substitution to create an efficient NIR emission. Synthesizing this compound, the obtained material exhibits a broadband NIR emission covering 700-1200 nm with a peak wavelength ranging from 820 to 860 nm depending on the Cr3+ substituting concentration. The Cr3+ concentration optimized sample possesses a photoluminescence quantum yield (PLQY) of 76.4% with an emission peak centered at 857 nm and a full width at half-maximum (fwhm) of 184 nm under 464 nm exaction, demonstrating an efficient and relatively long-wavelength NIR emission with wide spectral coverage. This broadband NIR emission is mainly derived from a single kind of emission center deduced from spectral analysis, luminescence dynamics, and first-principle calculations. Using this material, the fabricated NIR pc-LED device presents an excellent NIR output power and NIR photoelectric conversion efficiency, making this material attractive in practical applications of night-vision and bioimaging. Therefore, this work not only provides a broadband NIR material with superiorities of low cost, high efficiency, wide-range tunability, wide spectral coverage, and relatively long-wavelength NIR emission for spectroscopy applications but also highlights some clues to discover this kind of materials.