Blue Light Excitation Research Articles

Synthesis, optical characteristics and thermal stability of Mn4+-doped Na3GaF6 red-emitting phosphor for high-performance warm WLED

Nowadays, Mn4+-activated fluoride red phosphors with high color purity, strong zero phonon line emission and relatively short decay time are crucial for improving the optical performance of WLED and emerging applications. In this work, a series of red-emitting Mn4+-activated fluoride phosphors in consideration of the non-equivalent substitution of Mn4+ for Ga3+ in the Na3GaF6 host are synthesized via the coprecipitation method at room temperature. The use of different reaction solvents successfully regulates the morphology, size and luminescence intensity of the phosphor. Under blue light excitation, Na3GaF6:Mn4+ sample shows a bright narrow-band red emission with exceptional correlated color temperature (4029 K). Moreover, the emission of strong zero phonon line induces the outstanding color purity of red light (93%). In addition, the critical concentration of Mn4+ is determined to be 0.04 and the concentration quenching mechanism is also systematically discussed. Noticeably, when Na3GaF6:Mn4+ phosphor achieves maximum fluorescence emission, its fluorescence lifetime value is only 3.48 ms. Additionally, the theoretical calculated results demonstrate that Na3GaF6 host can provide strong crystal field strength for Mn4+, and the Racah parameters (B and C) and nephelauxetic ratio (β1) are used to evaluate the nephelauxetic effect of Mn4+, which is compared with other types of Mn4+-activated phosphors. The activation energy, chromaticity shift and chromaticity coordinate variation are systematically calculated to analyze the thermal stability of Na3GaF6:Mn4+ red phosphor. Meanwhile, by employing the as-prepared phosphor Na3GaF6:Mn4+ as a red component, a high-performance warm WLED shows a full spectrum emission, and the corresponding cold white light emission is also transformed into the warm white light emission (CCT = 4224 K, Ra = 89.1 and LE = 111.72 lm/W). Moreover, under high driving current, such WLED exhibits stable output light efficiency. These results suggest that Na3GaF6:Mn4+ as red phosphor has a stupendous potential for warm WLED in indoor lighting.

Robust efficiency stability and excellent aging resistance broadband NIR all-inorganic LEDs based on Tellurium-doped germanate glasses for multifunctional applications

Broadband near-infrared (NIR) spectroscopy based on glass-converted light-emitting diodes (gc-LEDs) has been of great interest to multifunctional applications ranging from night vision to chemical industry, stimulating the demand for exploring broadband NIR gc-LEDs with sufficient efficiency stability and aging resistance. Herein, an all-inorganic broadband NIR LEDs based on Te cluster-doped germanate glass is developed. Via adjustment of melting atmosphere and network topology of the glass matrix, active NIR Te cluster centers can be generated and stabilized in germanate glass and show a broad emission at 770 nm with a full width at half maximum (FWHM) of 260 nm under blue light excitation. By combining the Te-doped glass with a commercial blue LED chip, a high-performance NIR gc-LEDs is fabricated with an NIR output power of 14.21 mW@10.1% under a driving current of 400 mA. Particularly, the fabricated NIR-LED device exhibits high efficient stability with a relatively low-efficiency drop of 0.0023 %mA−1, and excellent aging resistance while retaining an electroluminescence intensity up 90 % of their initial value after aging for 480 h under harsh conditions, which is comparable to the commercial phosphors. Finally, its multifunctional application of gc-LEDs is also demonstrated.

Excitation-Selective and Double-Emissive Lead-Free Binary Hybrid Metal Halides for White Light-Emitting Diode and X-Ray Scintillation.

Zero-dimensional (0D) organic metal halides comprising heterogeneous metal cations in single phase can achieve multiple luminous emissions enabling them toward multifunctional light-emitting applications. Herein, A novel single crystal of (C8H20N)4SbMnCl9 containing two luminescent centers of [SbCl5]2- pentahedrons and [MnCl4]2- tetrahedrons is reported. The large distance between Sb-Sb, Mn-Mn, and Sb-Mn as well as theory calculation indicate negligible interaction between individual centers, thus endowing (C8H20N)4SbMnCl9 with excitation-dependable and efficient luminescence. Under near-UV excitation, only orange emission originates from self-trapped excitons recombination in [SbCl5]2- pentahedron occurs with photoluminescence quantum yield (PLQY) of 91.5%. Under blue-light excitation, only green emission originating from 4T1-6A1 transition of Mn2+ in [MnCl4]2- tetrahedrons occurs with PLQY of 66.8%. Interestingly, upon X-ray illumination, both emissions can be fully achieved due to the high-energy photon absorption. Consequently, (C8H20N)4SbMnCl9 is employed as phosphors to fabricate white light-emitting diodes optically pumped by n-UV chip and blue-chip thanks to its excitation-dependable property. Moreover, it also shows promising performance as X-ray scintillator with low detection limit of 60.79 nGyair S-1, steady-state light yield ≈54% of commerical scintillaotr LuAG:Ce, high resolution of 13.5 lpmm-1 for X-ray imaging. This work presents a new structural design to fabricate 0D hybrids with multicolor emissions.

Ni2+-doped MgTa2O6 phosphors capable of near-infrared II and III emission under blue-light excitation

Presently, Ni2+-activated near-infrared (NIR) phosphors still have disadvantages such as relatively short emission wavelength and narrow half-peak width, mismatched excitation wavelength to that of commercially available high-efficiency blue chips. Here, Ni2+-doped tetragonal MgTa2O6 NIR phosphor was successfully prepared by high-temperature solid phase method. The matrix material provided an octahedral lattice for Ni2+ to replace Ta5+ in the [TaO6] octahedron of the crystal lattice. Under the excitation of 470 nm blue light, Ni2+ was excited through 3T2(F)→3A2(F) spin-allowed transition and emitted an ultra-broadband NIR light that was 1300–2000 nm in wavelength, peaked ∼ 1620 nm, covered the NIR-II and NIR-III regions, had a full width at half maximum reached 297 nm, and a PLQY of 25.62 %. The unique ultra-broadband and long wavelength NIR emission by this phosphor was derived from Ni2+ which is situated in a weak crystal field environment due to space asymmetric distortion caused by a high charge polarization surrounding the center of the [TaO6] octahedron in a MgTa2O6 matrix. A NIR pc-LED was constructed using Ni2+-doped near-infrared phosphors packaged with a commercial high-efficiency blue LED chip (@ 470 nm), and its application prospect was demonstrated by NIR night vision monitoring and nondestructive imaging of venous in human fingers.

Realization of Broadband Near-Infrared Emission with High Thermal Stability in YGa3(BO3)4: Cr3+ Borate Phosphor.

As a key material for phosphor-converted light-emitting diodes (pc-LEDs) applications, broadband near-infrared (NIR) phosphors currently face poor thermal stability issues. In this work, we synthesized a broadband near-infrared phosphor YGa3(BO3)4: Cr3+ (YGBO: Cr3+) with a high thermal stability. The YGBO: Cr3+ sample exhibits a broadband near-infrared emission centered at 770 nm with a full width at half-maximum (fwhm) of 2130 cm-1 under blue light excitation. Benefiting from the borate host crystal's strong structural rigidity, wide optical band gap, and weak electron-phonon coupling strength, YGBO: Cr3+ demonstrates strong luminescence thermal stability, and the corresponding luminescence intensity can maintain 80% at 150 °C compared to room temperature. Furthermore, we fabricated a pc-LED device using a blue light chip and YGBO: Cr3+ phosphor, and confirmed its application potential as a near-infrared light source in the spectral analysis of fruit freshness.

Potential usage of cesium manganese halide for multi-functional optoelectronic devices: Display & photodetector application

The composition of manganese, which exhibits tetrahedral coordination with halogen ligands, makes it excellent for use in green light-emitting materials. In particular, zero-dimensional Cs3MnBr5 material has continuously been researched as a lead-free all-inorganic light emitting material. It has excellent optical properties such as center wavelength and full width at half maximum. The most recent studies on Cs3MnBr5 have synthesized it using a bottom-up method. However, the problem of notably poor particle uniformity or efficiency remains. The aim of this study was to develop sub-micron-sized Cs3MnBr5 particles with octahedron or truncated shapes by modifying the existing hot-injection synthesis method. Sub-micron Cs3MnBr5 particles showed 60% photoluminescence quantum yield (PLQY) under blue light excitation and absorbed light in the entire visible light region, including the absorption edge by PLE. Therefore, we explored existing research on light conversion films for LED & micro-LED and photodetector applications with a focus on optical properties of Cs3MnBr5 particles.

Ultrastructure, CO2 Assimilation and Chlorophyll Fluorescence Kinetics in Photosynthesizing Glycine max Callus and Leaf Mesophyll Tissues

The ultrastructural and functional features of photosynthesizing callus cells are poorly known. Electron microscopy studies on green, compact Glycine max calluses have shown that they are composed of photosynthesizing cells characterized by clear ultrastructural signs of senescence. Studies on chlorophyll fluorescence and CO2 assimilation kinetics have shown that such cells were still able to maintain photosynthesis but could not compensate for the respiratory CO2 uptake. Having a one-step CO2 assimilation kinetics, photosynthesis in calluses differed from photosynthesis in leaves, which had a two-step CO2 assimilation kinetics. In contrast to leaves, the fluorescence induction curves in G. max calluses strongly differed in shape depending on the color of actinic light (red or blue). Red (in contrast to blue) light excitation did not lead to CO2 assimilation in the calluses, thus suggesting anoxygenic photosynthesis in this case. In particular, the data obtained indicate that the actinic light spectrum should be considered when cultivating calluses for micropropagation of plants and for callus tissue research.

Illuminating the path to high-precision dual-mode optical thermometry: A Mn4+-activated oxyfluoride single crystal for a portable optical fiber thermometric platform

Multifunctional ratiometric and lifetime-technology dual-mode sensing plays a pivotal role in optical thermometry, yet poses substantial challenges in Mn4+-doped oxyfluorides/fluorides. Especially, despite of higher sensitivity, the applicability of lifetime-mode optical thermometers is generally restricted to large volume, highly integrated spectrometers. Here, a Mn4+-doped oxyfluoride single crystal Na2NbOF5:Mn4+ (NNOFM) is demonstrated as accurate dual-mode optical temperature sensor and developed into a portable optical fiber thermometric platform. Homogeneous NNOF shell is grown to improve the moisture resistant for extending operational lifespan. Under blue light excitation, two different temperature-sensitive sharp line vibrational transitions endow ratiometric mode temperature sensor. Importantly, rapidly decaying lifetime of Mn4+ produces high relative sensitivity Sr of 5.36 % K−1 at 448 K among Mn4+-based phosphors. Integrating NNOFM core–shell single crystal into optical fiber and coupling pulsed laser and oscilloscope, a portable optical fiber thermometric platform is realized. Accurate measurement result of boiling water being 373.33 K with quite small relative standard deviation to 0.04 % shows great potential of this fabricated thermometric platform for practical applications. This study not only enlightens the design of high-precision dual-mode optical thermometers in Mn4+-doped oxyfluorides/fluorides, but also illuminates the path to create portable optical fiber thermometric platforms.

Ultrastable quantum dot composites with dense barrier layer for wide color gamut display

Quantum dots (QDs) have showed great potential for next-generation lighting and display technologies. However, its stability is still one of the key problems that limit its practical application. In this paper, by comparing the specific surface area (SSA) and pore width of aluminum oxide (AlOx) and silicon oxide (SiO2) barrier layers, the relationship between the porosity of barrier layers and the stability of QDs was studied. The results showed that the synthesized SiO2-QD-AlOx, which has the smallest SSA in the synthesized QD composites, exhibited the best stability on the quantum dot diffuser plate (QD-DP). Moreover, the operational lifetime (T80) at 450 nm blue light excitation was increased by a factor of 3.41 compared to that of bare QDs. Meanwhile, the prepared QD-DP containing dense SiO2-QD-AlOx composites significantly improved the resistance to light, heat, moisture and oxygen. Finally, the prepared QD-DP was assembled into a Mini-LED TV with a wide color gamut and excellent display performance (a color gamut of 157.4 % for commercial normal TV, and 107.19 % for the National Television System Committee (NTSC 1931)). This technique provides favorable guide for effectively enhancing the stability of QDs in lighting and display technologies.

Photophysiologically active green, red, and brown macroalgae living in the Arctic Polar Night

Arctic macroalgae species have developed different growth strategies to survive extreme seasonal changes in irradiance in polar regions. We compared photophysiological parameters such as the light saturation parameter (Ek) and pigment composition of green, red, and brown macroalgae collected in January (Polar Night) and October 2020 (end of the light season). Macroalgae in January appeared healthier (morphologically) and had longer lamina (new growth) than those in October. EK values for red, and brown algae were higher with lower maximum quantum yield of PS II fluorescence (Fv/Fm) in January versus October. Furthermore, in January, new tissues in kelp species had higher EK than the older tissue. Higher EK and lower Fv/Fm during the Polar Night indicates that the photosynthetic apparatus is active but slow. Furthermore, we discuss Chlorophyll (Chl) a emission spectra under blue and green excitation light to determine the ratio of Chl a in photosystem II (PS II) vs photosystem I (PS I). Absorbance spectra of P. palmata was used to interpret the emission spectra. The observed spectral shifts in the absorbance and reflectance spectra of different macroalgae is discussed. Photophysiological methods provide health information complementary to future mapping and monitoring of macroalgae. These results reveal that macroalgae grow new tissue in darkness.

Efficient broadband yellow-emitting Mg2.5Lu1.5Al1.5Si2.5O12:Ce3+ garnet phosphors for blue-light-pumped white light-emitting diodes

The discovery of yellow-emitting phosphors with higher luminescence intensity and wider bandwidth than the commercial Y3Al5O12:Ce3+ (YAG:Ce3+) phosphor upon blue light excitation remains one of the significant challenges for establishing human-centered warm white light-emitting diode towards high-performance illumination. Herein, we innovatively synthesized a novel Ce3+-activated broadband yellow-emitting garnet phosphor of Mg2.5Lu1.5Al1.5Si2.5O12:Ce3+ (MLASO:Ce3+) via conventional high-temperature solid-state reaction method. The as-prepared MLASO:10%Ce3+ garnet sample possesses a cubic structure with Ia3‾d space group and lattice parameters of a = b = c = 11.85098 Å and V = 1664.421(0.044) Å3. Luminescence spectroscopy tests indicates that the optimal MLASO:10%Ce3+ yellow-emitting phosphor features 1.2 times higher relative integral luminescence intensity and an impressive full width at half maximum (FWHM) of up to 145 nm with respect to the most extensively available commercial YAG:Ce3+ phosphor (FWHM = 122 nm) under the identical blue light irradiation, which can provide more red-components for improving color rendering index. Additionally, the CIE color coordinates and a satisfactory internal quantum efficiency are determined to be (0.4751,0.5028) and 74%, respectively. More importantly, the representative optimal sample can preserve 77% luminescence emission intensity at a 423 K high temperature thermal treatment environment compared to the ambient temperature. As a result, this study sheds light on newly discovered broadband yellow-emitting MLASO:10%Ce3+ garnet phosphor containing more of the red chromatic spectrum can sever as one of the promising color-conversion-materials in high-performance white LEDs with high color rendering index for healthy solid-state lighting.

Highly efficient and stable near-infrared broadband luminescence in SrGa4O7:Cr3+, Yb3+ phosphor

Developing novel broadband near-infrared (NIR) phosphors is crucial to promote NIR phosphor-converted light emitting diodes (pc-LEDs) development. In this paper, a novel multifunctional near-infrared phosphor, SrGa4O7:Cr3+, Yb3+, was synthesized by the conventional high-temperature solid-state method. The emission band of the material spans from 650 nm to 1100 nm. Despite the predominance of four-coordinate and five-coordinate sites within the SrGa4O7 (SGO) lattice, the incorporation of Cr3+ ions induces distortion in the Ga–O tetrahedra, resulting in an octahedral environment for Cr3+. Under blue light excitation, the Cr3+ ions exhibit an ultra-wide emission band (650–900 nm) with a Full Width at Half Maximum (FWHM) of 131 nm. Furthermore, energy transfer from Cr3+ to Yb3+ was achieved in SrGa4O7:Cr3+, Yb3+, and the incorporation of an optimal quantity of Yb3+ co-dopant yielded a significantly enhanced and extraordinarily broad spectrum from 600 to 1100 nm. Moreover, Yb3+-codoping improves the thermal stability due to the energy transfer from Cr3+ to more thermally stable Yb3+ emitters, and the integrated intensity of SrGa4O7:Cr3+, Yb3+ at 300 K was 74% of that at room temperature. Based on these findings, a blue-light-excited NIR pc-LED was encapsulated. The forward voltage and intensity of the LED remained almost constant after 500 h of thermal aging at high temperatures, indicating its particular reliability in NIR pc-LED applications. The results show that SrGa4O7:Cr3+, Yb3+ phosphors have great potential in ultra-wideband NIR pc-LED applications.

Single Amino Acid Mutation Decouples Photochemistry of the BLUF Domain from the Enzymatic Function of OaPAC and Drives the Enzyme to a Switched-on State

Photoactivated adenylate cyclases (PACs) are light-activated enzymes that combine a BLUF (blue-light using flavin) domain and an adenylate cyclase domain that are able to increase the levels of the important second messenger cAMP (cyclic adenosine monophosphate) upon blue-light excitation. The light-induced changes in the BLUF domain are transduced to the adenylate cyclase domain via a mechanism that has not yet been established. One critical residue in the photoactivation mechanism of BLUF domains, present in the vicinity of the flavin is the glutamine amino acid close to the N5 of the flavin. The role of this residue has been investigated extensively both experimentally and theoretically. However, its role in the activity of the photoactivated adenylate cyclase, OaPAC has never been addressed. In this work, we applied ultrafast transient visible and infrared spectroscopies to study the photochemistry of the Q48E OaPAC mutant. This mutation altered the primary electron transfer process and switched the enzyme into a permanent ‘on’ state, able to increase the cAMP levels under dark conditions compared to the cAMP levels of the dark-adapted state of the wild-type OaPAC. Differential scanning calorimetry measurements point to a less compact structure for the Q48E OaPAC mutant. The ensemble of these findings provide insight into the important elements in PACs and how their fine tuning may help in the design of optogenetic devices.

High-Efficiency Narrow-Band Green-Emitting Manganese(II) Halide for Multifunctional Applications.

Zero-dimensional (0D) Mn2+-based metal halides used as luminescent materials and scintillators have become a research hotspot in the field of photoelectric materials and devices due to their unique composition, structure, and fluorescence properties. It is of great value to explore new Mn2+-based metal halides to achieve multifunctional applications. Herein, the novel 0D Mn2+-based metal halide single crystal (BPTP)2MnBr4 is synthesized by a simple solvent-antisolvent recrystallization method. Under excitation at 468 nm, the (BPTP)2MnBr4 single crystal shows a pronounced narrow-band green luminescence centered at 515 nm derived from the d-d transition of the Mn2+ ion. This emission has a relatively narrow full width at half maximum of 43 nm and a high photoluminescence quantum yield (PLQY) of 82%. In addition, (BPTP)2MnBr4 exhibits good thermal stability at 393 K with a retention of 79% of the initial photoluminescence intensity at 298 K. Benefiting from its strong blue light excitation, high PLQY, and good thermal stability, we manufacture an ideal white light-emitting diode (LED) device using a 460 nm blue LED chip, green-emitting (BPTP)2MnBr4, and commercial K2SiF6:Mn4+ red phosphor. Under 20 mA drive current, the LED shows a high luminous efficiency of 112 lm/W and a wide color gamut of 110.8%, according to the National Television System Committee standard. In addition, (BPTP)2MnBr4 crystals show a strong X-ray absorption. Based on the commercial Lu3Al5O12:Ce3+ scintillator, the calculated light yield of (BPTP)2MnBr4 reaches up to about 136,000 photons/MeV and the detection limit reaches 0.282 μGyair s-1. Additionally, a melt quenching approach is used to construct a (BPTP)2MnBr4 clear glass scintillation screen, realizing a spatial resolution of 10.1 lp/mm. The proper performances of (BPTP)2MnBr4 as phosphor-converted LED materials and the X-ray scintillator with the addition of eco-friendly, low-cost solution processability make 0D Mn2+-based metal halides potential luminescent materials for multifunctional applications.

Effects of different metal centers on the structure and luminescence properties of hybrid materials

Three novel inorganic-organic hybrid materials, [PbI3(BTA-1)]n (1) (BTA-1 = N-((1H-benzotriazole-1-yl)methyl)-N,N-dimethyl ethylammonium)，[Cu2I3(BTA-2)]n (2) (BTA-2 = 1-(1H-benzotriazole-1-yl)-N,N,N-trimethylammonium carbamate) and [ZnI3(BTA-3)]n (3) (BTA-3 = 3-(1H-benzotriazole-1-yl)-N,N,N-trimethylpropane-1-ammonium), have been was prepared by a solvent volatilization method. All three complexes have been characterized by single-crystal X-ray diffraction, powder X-ray diffraction (PXRD) and thermogravimetric (TG) analysis. Based on different metal iodides, they stack in different structural modes with different cluster cores, such as [PbI6]2- in complex 1, [Cu4I6]2- in complex 2 and [ZnI3N]2- in complex 3. The fluorescence analysis show that complex 1 and 2 produced green light when the excitation wavelength was 318 nm and 328 nm, respectively. While complex 3 exhibited near white light when the excitation wavelength was 424 nm (CIE: 0.332, 0.395). It shows that complex 3 can be used as a white light emitting material for direct blue light excitation.

Potential application of a non-contact tool using measurable autofluorescence in oral leukoplakia

ObjectiveA fluorescence-based mouth-observation device has recently been developed, which shines the oral mucosa with blue excitation light to visualize oral mucosal lesions; this visualization is based on the differences in autofluorescence between oral lesions and healthy mucosa. In recent years, it has received renewed attention in terms of infection control because of its non-contact protocol. This study used IllumiScan® (Shofu, Japan), a fluorescence device similar to a generic fluorescence visualization device, for the analysis of oral mucosal lesions. The study aimed to compare the relationship between the histopathological findings of leukoplakia and those obtained using IllumiScan®. MethodsFifty patients with a clinical diagnosis of oral leukoplakia and a histopathological diagnosis of epithelial dysplasia or hyperkeratosis were included. The brightness of leukoplakia was reported as G values and was compared with those of tissue images. The G values were obtained using IllumiScan® and used for further analysis. ResultsThe G values of areas surrounding the white lesions on the oral mucosa with epithelial dysplasia were significantly lower than those of areas surrounding white hyperkeratotic lesions and healthy mucosa. ConclusionsBy observing oral leukoplakia with the Illumiscan®, we were able to diagnose leukoplakia noninvasively by comparing G values in and around white lesions and applying fluorescence visualization retention and fluorescence visualization loss intensities.

Singlet-triplet dephasing in radical pairs in avian cryptochromes leads to time-dependent magnetic field effects.

Cryptochrome 4a (Cry4a) has been proposed as the sensor at the heart of the magnetic compass in migratory songbirds. Blue-light excitation of this protein produces magnetically sensitive flavin-tryptophan radical pairs whose properties suggest that Cry4a could indeed be suitable as a magnetoreceptor. Here, we use cavity ring-down spectroscopy to measure magnetic field effects on the kinetics of these radical pairs in modified Cry4a proteins from the migratory European robin and from nonmigratory pigeon and chicken. B1/2, a parameter that characterizes the magnetic field-dependence of the reactions, was found to be larger than expected on the basis of hyperfine interactions and to increase with the delay between pump and probe laser pulses. Semiclassical spin dynamics simulations show that this behavior is consistent with a singlet-triplet dephasing (STD) relaxation mechanism. Analysis of the experimental data gives dephasing rate constants, rSTD, in the range 3-6 × 107s-1. A simple "toy" model due to Maeda, Miura, and Arai [Mol. Phys. 104, 1779-1788 (2006)] is used to shed light on the origin of the time-dependence and the nature of the STD mechanism. Under the conditions of the experiments, STD results in an exponential approach to spin equilibrium at a rate considerably slower than rSTD. We attribute the loss of singlet-triplet coherence to electron hopping between the second and third tryptophans of the electron transfer chain and comment on whether this process could explain differences in the magnetic sensitivity of robin, chicken, and pigeon Cry4a's.

Zero thermal quenching and suppressed concentration quenching in a highly efficient structure‐confined fluoride near-infrared phosphor

The development of thermally stable and efficient broadband near-infrared (NIR) phosphors suffers from severe hindrance. Herein, a unique anti-fluorescence quenching is realized in a novel Cs2NaGaF6: Cr3+ NIR fluoride phosphor with a strategy of integrating the structural confinement effect with weak electron-phonon coupling effect. Upon blue light excitation, this phosphor exhibits a wide emission band with a peak wavelength of ∼789 nm and a full width at half maximum (FWHM) of 117 nm. Thanks to the structural confinement effect, a large quenching content of 20 mol% and a high internal quantum efficiency (IQE) of 87.4% are achieved, showing a suppressed concentration quenching behavior. Significantly, Cs2NaGaF6: 0.20Cr3+ phosphor possesses an abnormal zero thermal quenching, which could be related with the weaker electron-phonon coupling effect. The emission intensity of Cs2NaGaF6: 0.20Cr3+ at 423 K can maintain up to 101.96% of that at 298 K. A fabricated NIR phosphor-converted light-emitting diode (pc-LED) exhibits an output power of 57.71 mW and a photoelectric conversion efficiency as high as 19.24% at 100 mA. Finally, utilizing a high-power NIR LED as the illuminant for traffic surveillance, significant information can be captured even in low-visibility environments. As a result, Cs2NaGaF6: Cr3+ possesses tremendous prospects in high-power NIR LEDs.

Efficient Ultra‐Broadband Phosphors for High-Power Near-infrared LED and night vision imaging system sources

Broadband near-infrared (NIR)-emitting materials have critical applications in biology, medical detection, and NIR night-vision. However, developing NIR phosphors with promising optical properties and excellent thermal stability is a great challenge for research. In this work, a novel NIR phosphor Cr3+ and Yb3+ doped CaSc2O4 (CSO) is an evolving NIR emitting phosphor with decent optical properties, boosted emission intensity, and thermal stability that makes it a promising candidate with potential applications in NIR-LED and infrared night-vision. The implications of the fundamental electronic structure of CSO, including valence-band (VB) and conduction-band (CB) orbital character, are investigated. Under blue light excitation, CSO:Cr3+ is settled with pure broadband NIR emissions (max = 920 nm, FWHM (full width at half maximum) = ∼310 nm) and good thermal stability. The occupation of two selectable lattice sites of Cr3+ in CSO is discussed in detail. Furthermore, emission enhancements of samples are done by Cr3+ and Yb3+ codoping, effectively broadening FWHM to 351 nm and reducing thermal quenching. The energy transfer (ET) routes in CSO:Cr3+,Yb3+ are investigated based on PL lifetime and comprehensive kinetic ET model, revealing that the PL enhancements by Cr3+ and Yb3+ codoping mainly originate from the ET from Cr3+ to Yb3+ emitters with more efficient and thermally stable. Finally, an InGaN-LED device encapsulated using CSO:0.01Cr3+ and CSO:0.01Cr3+,0.01 Yb3+ phosphor was fabricated. The fabricated NIR pc-LEDs are excellent candidates for NIR light sources in biological imaging and NIR night vision.

The development of a new efficient red phosphor based on Eu2+ doped traditional inorganic oxygenate-perovskite compounds

The halide-perovskite type phosphors have been aroused extensive attention in recent years for their high quantum efficiency, but traditional oxygenate-perovskite type phosphors with Eu2+ activator have not been studied extensively so far. To fill this void, we dope Eu2+ into a typical perovskite host lattice SrZrO3 to produce an efficient phosphor SrZrO3:xEu2+. Theoretical calculation reveals that SrZrO3 has an indirect band gap of 3.776 eV. Phosphors SrZrO3:xEu2+ show bright red emission peaking at 605 nm under 450 nm blue light excitation with the full width at half maximum (FWHM) of 60 nm. The optimized concentration of Eu2+ is x = 0.10, and the quenching mechanism originates from the dipole-dipole interactions. The external quantum yield of optimal sample, SrZrO3:0.10Eu2+ can reach up to a high value of 50%. Temperature dependent luminescent properties studies show that the fluorescence integrated intensity of the sample at 425 K remains at 80% of that at 300 K. Finally, a white light-emitting diode (LED) is fabricated with color rendering index of 73 and color temperature of 3576 K. Thus, phosphor SrZrO3:0.10Eu2+ has great potential in fields of WLED lamp.