Near-infrared Light Source Research Articles

Long-term noninvasive cardiac monitoring via Neutralized interfacial design for noise-suppressed near-infrared organic photodetectors

Organic photodetectors (OPDs) are the prime candidates for realizing commercial photoplethysmography (PPG) sensors in the future, although their performance and stability limitations remain as challenges. This study presents a strategy for fabricating high-precision, long-term, sustainable OPDs for non-invasive cardiac monitoring. In this work, the use of appropriate amounts of heterocyclic 1,3-diazoles (solid surfactants) enhances the morphology of PEDOT:PSS films and optimizes its energy level alignment, thus directly reducing the leakage current noise and improving the stability of the OPD. The OPDs with 0.5 wt% heterocyclic 1,3-diazole demonstrate enhanced dark current suppression and detectivity enhancement in the photoconductive and self-powered modes. Improved charge recombination dynamics and optimal resistance ratios lead to better performance of the champion device under low-intensity illumination. The champion device yields a more precise Photoplethysmography (PPG) signal under normal and exercise conditions when using a near-infrared light source, and it maintains a PPG signal intensity of more than 90 % after 315 days (7560 h) of storage in a nitrogen atmosphere. Optimized PPG sensors based on flexible substrates maintain signal intensity after seven days of air storage. The low hysteresis behavior also verifies that the optimized device has higher driving stability. High-reliability, high-validity accelerated photoplethysmography (APG) demonstrated that the champion PPG sensor would be used for accurate cardiovascular diagnostics, even over an extended period.

Structure regulation and luminescence improvement of Gd3Ga5O12:Cr3+: An anti-thermal quenching NIR phosphor for multifunctional applications

Near-infrared (NIR) phosphors converted light emitting diodes (LEDs) are booming as next NIR light sources. But the quantum efficiency and thermal stability of the NIR phosphors need to be improved. Here, thermally stable garnet Gd3Ga5O12 is selected as the matrix and Cr3+ as the luminescent center to obtain Gd3Ga5O12:Cr3+ NIR phosphor. Equivalent smaller Lu3+ was adopted to regulate the structure of Gd3Ga5O12 to further improve the luminescence performance. By regulating the structure the emission spectra shift toward blue region and the intensity is improved. Optimized GdLu2Ga5O12:Cr3+ exhibits anti-thermal quenching behavior and the internal quantum efficiency reaches 73.69 %. Relative sensitivity value of the phosphor GdLu2Ga5O12:Cr3+ reaches 3.353 % K−1 at 423 K based on lifetime mode. LED device is fabricated by combining the phosphor GdLu2Ga5O12:Cr3+ and the commercial red phosphor with blue chip. Electroluminescence spectrum can cover the absorption spectra of the plant dyes well. The lettuce grow faster by adopting this LED device as compensating light source. This work provides an anti-thermal quenching NIR phosphor for multiple applications.

Near-infrared luminescence in Ca3ZnMGe3O12:Cr3+ (M = Zr, Hf, Sn, Ti) garnet family for light-emitting diode applications

Near-infrared (NIR) phosphors as crucial components of NIR light sources have multifunctional and smart spectroscopy applications, prompting an increasing research interest in developing efficient and stable NIR materials. Focusing on this issue, the present study explored the luminescent properties of Cr3+-doped Ca3ZnMGe3O12 (M = Zr, Hf, Sn and Ti) garnet family. These materials exhibit an emission peak falls within the range of 785–805 nm with a full width at half maximum (FWHM) varying from 114 to 123 nm. Among them, the Ca3ZnZrGe3O12:Cr3+ phosphor shows the highest photoluminescence quantum yield (PLQY = 60.3 %) and an excellent thermal stability (I423K/I298K = 77.51 %). Moreover, the performance of a prototype Ca3ZnZrGe3O12:Cr3+-containing NIR pc-LED device was estimated, which achieves an NIR output of 23.46 mW and a photonic efficiency of 14.09 % under 100 mA driving current. Non-destructive examination can be realized using this light source, demonstrating the good potential of the material in NIR spectroscopy applications.

A Cr3+-Yb3+ co-doped high-efficiency near-infrared luminescent phosphor for NIR-II light source applications

Phosphor conversion light-emitting diode (PC-LED) technology has become a focal point of research for portable near-infrared light sources in recent years. One of the crucial aspects is to develop phosphor materials that can be effectively stimulated by commercial available blue light. Unfortunately, efficient phosphors in the NIR-II that can be excited by commercial blue light are particularly scarce. In this study, Mg4Ta2O9:0.04Cr3+,0.03Yb3+,0.07Li+ (MTO:0.04Cr3+,0.03Yb3+,0.07Li+) phosphor was synthesized using the high temperature solid phase method, and its emission spectrum covered the first and second near-infrared windows (700–1200 nm). The internal quantum efficiency (IQE) and external quantum efficiency (EQE) are 88.7 % and 45.6 %, respectively, due to the synergistic effect of energy transfer and Li-ion modification. Additionally, the doping of Yb3+ ions and Li+ ions enhances the thermal stability of luminescence. The thermal stability of MTO:0.04Cr3+,0.03Yb3+,0.07Li+ and MTO:0.04Cr3+,0.03Yb3+ is 9.81 % and 14.43 % higher, respectively, than that of MTO:0.04Cr3+,0.03Yb3+ and MTO:0.04Cr3+. To evaluate its potential applications, we developed a prototype PC-LED utilizing MTO:0.04Cr3+,0.03Yb3+,0.07Li+ phosphor as an emission emitter which demonstrated advantages in biomedical imaging, night vision, and non-destructive testing.

Cr3+ and Ni2+ Co-doped near-infrared dual-emission garnet phosphor for spectroscopic applications

Near infrared spectroscopy is a simple, fast, and non-invasive technique for detecting the composition of substances. However, most NIR phosphors cannot cover the near-infrared I and II regions, which limits the types of substances that can be detected. Herein, Cr3+, Ni2+ co-activated NIR Y3Al2Ga3O12(YAGG) garnet phosphors were synthesized via high-temperature solid-phase method. Due to the energy transfer from Cr3+ to Ni2+, the emission spectra of YAGG: Cr3+, Ni2+ are composed of NIR I emission of Cr3+ at 710 nm and NIR II emission of Ni2+ at 1420 nm. The measured internal and external quantum efficiencies of YAGG: 0.08Cr3+, 0.005Ni2+ under 450 nm excitation are 54.4 %, and 26.7 %, respectively. This sample was selected to fabricate pc-LEDs, and fill the emission spectrum gap with Mg2GeO4: 0.01Cr3+. The pc-LED fabricated with PiG film do not exhibit strong characteristic absorption in NIR II region, significantly reduce the re-absorption and thermal quenching of the phosphors. The electro-optical conversion efficiency of PiG pc-LED reaches 6.49 % at 10 mA; The results indicate that YAGG: Cr3+, Ni2+ and the fabricated NIR pc-LED are good near-infrared substance detection light source scheme.

Near-infrared luminescence shift in Ni2+-doped double perovskite phosphors

For applications such as near-infrared (NIR) spectroscopy requiring energy-efficient and compact broadband NIR light sources, a variety of Ni2+-doped phosphors emitting in the 1100–2000 nm range has been developed. However, the commercialization of Ni2+-doped NIR phosphors has not yet been achieved, and material exploration is ongoing. To gain insight into the luminescence properties of Ni2+, including emission wavelength and efficiency influenced by compositional and structural variations, Ni2+-doped double-perovskite AELaMgTaO6:Ni2+ (AE = Ba, Sr, or Ca) ceramic samples were synthesized, and their optical properties were examined. Because the energy of the Ni2+ 3d-3d transition is sensitive to structural variations in the local environment around the Ni2+ ions, we investigated the variation in optical properties by indirect ligand field engineering of NiO6 octahedra following the substitution of alkaline earth ions AE2+. The prepared AELaMgTaO6:Ni2+ samples were Ba-Sr or Ba-Ca complete solid solution systems with cubic-to-monoclinic phase transitions. The broad NIR luminescence band at ∼1350–1700 nm was blue-shifted by ∼100 nm, accompanied by Sr2+ or Ca2+ substitution. The local symmetry of the NiO6 octahedra was reduced from Oh to Ci owing to the phase transition, resulting in an enhancement of the NIR luminescence intensity and an increase in the quenching temperature. This study demonstrated that Ni2+ phosphors with the desired optical properties for NIR spectroscopy applications can be designed by controlling the composition ratio of the host compounds and the resultant variation in the local environment of the solid solution compounds.

Co-training machine learning enables interpretable discovery of near-infrared phosphors with high performance

Near-infrared (NIR) phosphors based on Cr3+ doped garnets present great potential in the next generation of NIR light sources. Nevertheless, the huge searching space for the garnet composition makes the rapid discovery of NIR phosphors with high performance remain a great challenge for the scientific community. Herein, a generalizable machine learning (ML) strategy is designed to accelerate the exploration of innovative NIR phosphors via establishing the relationship between key parameters and emission peak wavelength (EPW). We propose a semi-supervised co-training model based on kernel ridge regression (KRR) and support vector regression (SVR), which successfully establishes an expanded dataset with unlabeled dataset (previously unidentified garnets), addressing the overfitting issue resulted from a small dataset and greatly improving the model generalization capability. The model is then interpreted to extract valuable insights into the contribution originated from different features. And a new type NIR luminescent material of Lu3Y2Ga3O12: Cr3+ (EPW~750 nm) is efficiently screened, which demonstrates a high internal (external) quantum efficiency of 97.1% (38.8%) and good thermal stability, particularly exhibiting promising application in the NIR phosphor-converted LEDs (pc-LED). These results suggest the strategy proposed in this work could provide new viewpoint and direction for developing NIR luminescence materials.

Near-infrared spectroscopy for glucose detection in aqueous solution

This work presents a near-infrared spectroscopy-based technique to measure the glucose concentration in an aqueous solution. A near-infrared light source sends optical energy through a glucose-water solution. The energy transmitted through the aqueous solution is received by a photodetector and a conditioning circuit that includes an operational amplifier and a low-pass filter to remove high-frequency noise. The received light intensity converted to DC voltage is found to be inversely proportional to the glucose concentration in the aqueous solution. The experimental results for glucose concentration in the range of 0–4000 mg/dL confirm the expected theoretical behavior. The sensitivity of the system is 26.25 μV/mgdL-1. The proposed glucose detection system is a promising tool for monitoring glucose levels in various industries, including food and beverage quality and healthcare.

La3Sc2Ga3O12:Cr3+, Nd3+ near-infrared phosphor for nondestructive detection and luminescence thermometry

To develop continuous broadband emission near-infrared (NIR) phosphors compatible with blue LED chips, numerous Cr3+-Yb3+ co-doped phosphors have been synthesized. However, the emission spectra of Cr3+ vary significantly across different matrix materials, while Yb3+ maintains a relatively stable emission spectrum. This variation leads to notable luminescence depressions between 850 and 900 nm in many Cr3+-Yb3+ co-doped phosphors. To address this emission spectrum gap, we utilized Cr3+ as a sensitizer and introduced Nd3+ as the luminescence center within the La3Sc2Ga3O12 matrix material, establishing a Cr3+-Nd3+ energy transfer channel. Under 480 nm excitation, we tuned emission peaks at 800 nm (Cr3+) and 881 nm (Nd3+). The stable NIR emission of Nd3+ effectively compensates for the missing spectrum in Cr3+-Yb3+ co-doping. The Cr3+-Nd3+ energy transfer process was thoroughly analyzed using diffuse reflection spectrum, excitation spectrum, and fluorescence decay curves. The LSGO:0.125Cr3+, 0.03Nd3+ compound with the best optical performance was packaged with a 480 nm LED chip to create a NIR light source. At a working current of 10 mA, it achieved a photoelectric conversion efficiency of 9.45 %, demonstrating its potential for applications in non-destructive detection and luminescence thermometry. This work presents a novel strategy for tuning NIR spectral distribution and developing continuous broadband NIR phosphors.

High-Performance Tunable Near-Infrared Emitters of Cr3+-Activated Garnet Phosphor Enabled by Chemical Unit Co-Substitution.

The escalating demand for portable near-infrared (NIR) light sources has posed a formidable challenge to the development of NIR phosphors characterized by high efficiency and exceptional thermal stability. Taking inspiration from the chemical unit co-substitution strategy, high-performance tunable (Lu3- xCax)(Ga5- xGex)O12:6%Cr3+ (x = 0-3) phosphors are designed with an emission center from 704 to 780nm and a broadest full width at half maximum (FWHM) of up to 172nm by introducing Ca2+ and Ge4+ ions into the garnet structure. In particular, Lu3Ga5O12:6%Cr3+ demonstrates an anti-thermal quenching phenomenon (I423K = 113.1%). Compared to Lu3Ga5O12:6%Cr3+, Lu2CaGa4GeO12:6%Cr3+ exhibits significantly improved FWHM and IQE by 108nm and 25.5%, respectively, while maintaining good thermal stability (I423K = 80.4%). Finally, Lu2CaGa4GeO12:6%Cr3+ phosphor is combined with a 465nm blue LED chip to fabricate NIR LED devices, exhibiting a NIR electroluminescence efficiency of 13.31%@100mA and demonstrating successful applications in nocturnal illumination and biomedical imaging technology. This work offers a fresh perspective on the design of highly efficient NIR garnet phosphors.

Remarkable broadband NIR emission of BaCa2MgSi2O8:Cr3+ phosphors and Eu2+ co-doping modulation

Developing high-performance broadband NIR (near-infrared) phosphors remains a crucial pursuit for the next-generation smart NIR light source. This study demonstrates the successful synthesis of BaCa2MgSi2O8:Cr3+ phosphors exhibiting exceptional broadband NIR emission via a high-temperature solid-state reaction. Notably, the 0.03Cr3+ doped composition, under 485 nm excitation, shines with a remarkable broadband emission spanning 700 nm–1100 nm and boasts a full width at half maximum (FWHM) of 134 nm. This work meticulously explores the intricate interplay between Cr3+ doping concentration, temperature, crystal field strength, and the Huang-Rhys parameter, shedding light on the underlying luminescence mechanisms. Moreover, the BaCa2MgSi2O8:0.03Cr3+ phosphor exhibits exceptional thermal stability, retaining approximately 70 % of its integrated emission intensity at 425 K compared to room temperature. To further expand the excitation range, Eu2+ was introduced as a co-dopant, successfully broadening the excitation spectrum to encompass nearly the entire ultraviolet–visible region (ranging from 250 nm to 750 nm). The presence of Eu2+→Cr3+ energy transfer was elucidated, and the impact of Eu2+ doping was thoroughly investigated. Moreover, the synthesized phosphor has been successfully integrated into a NIR phosphor-converted light-emitting diode (pc-LED), showcasing their potential application in the realms of night vision and NIR vascular imaging. These findings offer invaluable insights into Cr3+ luminescence behavior and pave the way for the development of novel NIR phosphors with enhanced functionalities, propelling us closer to the realization of next-generation smart lighting solutions.

Cr3+-Yb3+ energy transfer drives ultra-wideband thermally-stable NIR-emitting Sr3Sc2Ge3O12 garnet phosphors for pc-LED application

The development of medical, military, and other fields has greatly increased the demand for broadband near-infrared light sources. This article reports that Sr3Sc2Ge3O12: Cr3+ (SSGO: Cr3+), a broadband near-infrared phosphor with 850 nm as the luminescence center, has an emission spectrum covering 700–1200 nm and a full width at half maximum (FWHM) of 125 nm under 490 nm excitation. To further increase the FWHM value, Yb3+ is introduced into the phosphor of SSGO: Cr3+ to enable energy transfer from Cr3+ to Yb3+. After doping 1 % of Yb3+ onto the Sr2+ site, the near-infrared emission generated by the 4A2→4T1(4P) transition of Cr3+ and the near-infrared emission generated by the 2F5/2 → 2F7/2 transition of Yb3+ work so that the FWHM increases to 220 nm. In addition, the thermal stability of the phosphor after co-doping with Yb3+ is also greatly enhanced from 61.6 % to 75.1 % by comparing it to the Cr3+ single-doped sample. In addition, SSGO:0.08Cr3+, 0.01 Yb3+ was combined with a commercial 490 nm chip to prepare a broadband near-infrared light-emitting diode (pc-LED).

Broadband NIR phosphor Gd3Lu2Ga3O12: Cr3+, Yb3+ with high thermal stability

Broadband near-infrared (NIR) phosphor-converted light-emitting diodes (pc-LEDs) have become important as new NIR light sources in NIR spectroscopy and NIR imaging techniques. However, currently developed broadband NIR phosphors commonly suffer from weak emission and poor thermal stability. In this work, a series of Gd3Lu2Ga3O12: Cr3+ phosphors were synthesized via high-temperature solid-state reaction. Under 460 nm excitation, the phosphors exhibit an intense emission spanning from 650 to 1150 nm with a full width at half maximum (FWHM) of 122 nm. After introducing Yb3+ as a co-dopant, the emission of the phosphor has been broadened greatly. Interestingly, the studied phosphors demonstrate super high thermal stability in a wide temperature range of 35–560 K, with the integrated emission intensity fluctuating within 10 %. At 435 K, the emission intensity of Gd3Lu2Ga3O12: 0.03Cr3+ remains 99.5 % and Gd3Lu2Ga3O12: 0.03Cr3+, 0.01 Yb3+ keeps 102.7 % of the initial intensity at room temperature. These NIR phosphors have been encapsulated with a common commercial 460 nm blue LED chip to fabricate a pc-LED device. The NIR output power of the device reaches 23.93 mW@100 mA, with a photoelectric conversion efficiency of 9.81 % at 20 mA current. The applications of the prepared NIR light source in night vision, and bioimaging have been demonstrated. The results show that these Cr3+/Yb3+ doped garnet phosphors can be effectively used in NIR light sources.

Unlocking Cr3+-Cr3+ Coupling in Spinel: Ultrabroadband Near-Infrared Emission beyond 900 nm with High Efficiency and Thermal Stability.

Broadband near-infrared (NIR) phosphor-converted light-emitting diodes (pc-LEDs) hold promising potential as next-generation compact, portable, and intelligent NIR light sources. Nonetheless, the lack of high-performance broadband NIR phosphors with an emission peak beyond 900 nm has severely hindered the development and widespread application of NIR pc-LEDs. This study presents a strategy for precise control of energy-state coupling in spinel solid solutions composed of MgxZn1-xGa2O4 to tune the NIR emissions of Cr3+ activators. By combining crystal field engineering and heavy doping, the Cr3+-Cr3+ ion pair emission from the 4T2 state is unlocked, giving rise to unusual broadband NIR emission spanning 650 and 1400 nm with an emission maximum of 913 nm and a full width at half-maximum (fwhm) of 213 nm. Under an optimal Mg/Zn ratio of 4:1, the sample achieves record-breaking performance, including high internal and external quantum efficiency (IQE = 83.9% and EQE = 35.7%) and excellent thermal stability (I423K/I298K = 75.8%). Encapsulating the as-obtained phosphors into prototype pc-LEDs yields an overwhelming NIR output power of 124.2 mW at a driving current of 840 mA and a photoelectric conversion efficiency (PCE) of 10.5% at 30 mA, rendering high performance in NIR imaging applications.

Ultra-broadband near-infrared emission of Cr3+-containing oxy-fluoride glass-ceramics

Broadband near-infrared (NIR) light sources cover unique optical wavelengths and are valuable in the fields of bioimaging and photodynamic therapy, night vision lighting and security monitoring. NIR phosphor converted light-emitting diode (NIR pc-LED) devices have attractive features such as tunable emission peak, low cost of production, compact in sizes and high luminous efficiency. However, heat accumulation during operation due to poor thermal conductivity of the organic resin used in packaging often causes serious reduction in luminous efficiency and accelerated degradation of the device. In present work, we developed a Cr3+-doped transparent CaF2-based oxy-fluoride glass-ceramic (GC) that showed a broadband emission of 700∼1400 nm under 470 nm excitation. The emission peaked at ∼880 nm, the full-width at half maximum was about ∼297 nm, and the photoluminescence quantum yield reached ∼31.19 %. The emission was derived from the electronic transition of Cr3+ ions from the 4T2(F) to 4A2(F). Through structural analysis and numerical simulation, we showed that during the heat treatment process, Cr3+ ions were enriched into the CaF2 crystal phase and replaced the Ca2+ in the GC host with occupied the center position of the polyhedrons, which provided a weak crystal field and led to NIR emission. We built NIR pc-LED devices using optimized GC and commercial blue LED chips, and we demonstrated the application of this NIR pc-LED in night-vision lighting. Our approaches to prepare simple and stable inorganic NIR luminous materials sealed in bulk in a transparent CaF2-based oxy-fluoride GC and to construct pc-LED devices could provide new concept to the field and have practical implications to applications in related fields.

Synthesis and luminescent properties of highly thermally stable GdGa3(BO3)4:Cr3+ broadband near-infrared phosphors for near-infrared LED applications

Developing near-infrared (NIR) phosphors with high thermal stability and broadband emission is pivotal for advancing NIR light sources. In this study, we synthesized a novel borate phosphor, GdGa3(BO3)4:Cr3+, via a high-temperature solid-state reaction. This phosphor demonstrates exceptional thermal stability, maintaining 94 % of its initial intensity even at 150 °C. Upon blue light excitation, it emits a broad spectrum from 650 to 1100 nm, peaking at 770 nm with a full width at half maximum (FWHM) of ∼130 nm. We conducted a comprehensive investigation to understand the mechanisms underlying its thermal stability. Additionally, by combining the GdGa3(BO3)4:15%Cr3+ phosphor with a commercial blue light chip, we fabricated an NIR LED device achieving a NIR output power of 6.45 mW and a photoelectric conversion efficiency of 1.57 % at 120 mA. This study offers valuable insights into the design of advanced NIR phosphors with superior thermal stability for NIR light source applications.

Development and optimisation of a near-infrared spectroscopic system for glucose quantification in aqueous and intralipid-based samples

A non-invasive glucose sensing device could revolutionise diabetes treatment. Near Infrared (NIR) spectroscopy is a promising technology for glucose sensing; however, the design and choice of components for NIR spectroscopy can greatly affect the sensing accuracy. We aimed to develop a NIR absorption spectroscopy system to determine liquid glucose concentrations in the physiological range, by evaluating a range of NIR photodetector components and light sources. Three detection assemblies were tested: (i) a dispersive spectrometer with photodiode array, (ii) a Czerny–Turner monochromator with InGaAs photodiode and (iii) a miniature Fourier Transform Infrared (FTIR) spectrometer. A halogen lamp and NIR globar were trialled as potential light sources. The components were systematically tested by comparing the coefficient of determination and standard error of prediction (SEP) for the same set of aqueous glucose samples through 10 mmol l−1 concentration steps. The Czerny–Turner monochromator with InGaAs photodiode, along with the globar, were identified as the optimal components for the system. A range of concentration steps (1–10 mmol l−1) were scanned to identify the physiologically relevant limit of detection, which was identified as 5 mmol/l for glucose in solution. Spectra were then collected from glucose samples in 10% intralipid suspension in the 10–20 mmol l−1 range and the equivalent concentrations in solution. The SEP was greater for the intralipid samples due to strong scattering. Scattering was dominant above 1300 nm, whilst absorption was dominant below 1300 nm. Although alternative approaches achieve better resolution, our system uses simple and readily-available components and presents a platform for a non-invasive NIR glucose sensing device.

Two-Site Occupation for Constructing Double Perovskite BaLaMgNbO6:Cr3+ Ultrabroadband NIR Phosphors.

Given the escalating significance of near-infrared (NIR) spectroscopy across industries, agriculture, and various domains, there is an imminent need to address the development of a novel generation of intelligent NIR light sources. Here, a series of Cr3+-doped BaLaMgNbO6 (BLMN) ultrabroadband NIR phosphor with a coverage range of 650-1300 nm were developed. The emission peak locates at 830 nm with a full width at half maximum of 210 nm. This ultrabroadband emission originates from the 4T2→4A2 transition of Cr3+ and the simultaneous occupation of [MgO6] and [NbO6] octahedral sites confirmed by low photoluminescence spectra (77-250 K), time-resolved photoluminescence spectra, and electron paramagnetic resonance spectra. The fluxing strategy improves the luminescence intensity and thermal stability of BLMN:0.02Cr3+ phosphors. The internal quantum efficiency (IQE) is 51%, external quantum efficiency (EQE) can reach 33%, and thermal stability can be maintained at 60%@100 °C. Finally, we successfully demonstrated the application of BLMN:Cr3+ ultrabroadband in the qualitative analysis of organic matter and food freshness detection.

Cr3+ activated Gd3Sc2Al3O12 garnet phosphor ceramic with broadband emissions and enhanced thermal stability toward high-power near-infrared LED/LD

The development of high-quality phosphor ceramics with high photoelectric efficiencies and thermal stabilities is essential for realizing high-power broadband near-infrared light sources. In this study, a series of pure-phase Gd3Sc2Al3O12:Cr3+ near-infrared (NIR) phosphor ceramics (GdScCr NIR-PCs) exhibiting remarkable thermal stability and broadband emission were fabricated for the first time using a vacuum sintering technique. The integrated emission intensity at 423 K is 79.8 % of that at room temperature. The GdSc08Cr exhibits an emission peak at a wavelength of 785 nm, with a full width at half maximum (FWHM) of 116.9 nm under 460 nm excitation. By integrating the GdScCr NIR-PC with a blue light-emitting diode/laser diode (LED/LD) excitation source, the NIR LED prototype achieved a maximum output power of 112.19 mW at 300 mA with a photoelectric conversion efficiency of 13.64 % at 150 mA, and the NIR LD prototype achieved a maximum power output of 484.34 mW at 2.3 A. The operating temperatures of NIR-PCs were 73.1 °C at 300 mA for LED and 90.7 °C at 2.5 A for LD. Moreover, the application of the prepared GdScCr NIR-PCs for fruit and grain detection was performed. These results demonstrate that the prepared GdScCr NIR-PCs possess substantial potential for application in high-power broadband NIR spectroscopy.

High-average-power single-frequency pulse optical parametric oscillator based on pulse-integrated seed-injection automatic locking.

Near-infrared nanosecond (ns) single-longitudinal-mode (SLM) pulse light generated from an optical parametric oscillator (OPO) is an important source in nonlinear optics and high-precision spectral analysis. In this Letter, a stable SLM near-infrared ns pulse light source generated from the OPO is presented, which is achieved by developing a seed-injection automatic locking technique based on a pulse-integrated photodetector (PIPD). Depending on the PIPD, the peak power of the pulse light detected by the photodiode is converted to the average power by integrating several pulses. As a result, the detector saturation is thoroughly eliminated, and the interference signal including the resonance point between seed and pulse lights can easily be attained by scanning the resonator length. On this basis, a microcontroller unit (MCU) is employed to realize automatic locking by looking for the minimum value of the interference signal. Finally, a SLM 824 nm pulse light source with an output power of 20.5 W and a linewidth of 51.42 MHz is obtained. The presented method can pave the way to implement a low-cost and compact high-average-power SLM pulse OPO.