Electro-optical Conversion Efficiency Research Articles

Antithermal-Quenching Near-Infrared Emitting Lu2SrAl4SiO12:Cr3+ Garnet-Type Phosphor for High-Resolution Nonvisual Imaging.

Near-infrared (NIR) light allows fast and nondestructive detection with deep penetration into biological tissues and is widely used in food inspection, biomedical imaging, night vision security, and other fields. Cr3+-doped NIR first region (NIR-I) phosphors have many interesting features that have attracted a lot of attention recently. However, practical issues, such as low photoluminescence quantum efficiency and poor thermal stability, need to be addressed. We synthesized Cr3+-doped Lu2SrAl4SiO12 garnet-type phosphors using a high-temperature solid-state reaction method. Under blue-light (@ 430 nm) excitation, the phosphors exhibited broadband NIR-I emission in the range of 600-1000 nm, with an emission peak at 710 nm. This system is unique, as the emission had multipeak sharp-line superposition and the Cr3+ ions were situated in a relatively strong crystal field environment, as opposed to a weak crystal field environment for other matrix. The optimal doping content of Cr3+ ions was 2 mol %, and its internal quantum efficiency was ∼76.8%. Surprisingly, this NIR phosphor showed an antithermal quenching effect, and the integrated luminescence intensity of NIR-I emission measured at 573 K was 206.3% of that measured at 303 K. We found that the antithermal quenching of NIR-I luminescence was caused by the extremely low thermal expansion coefficient and rigid structure of the Lu2SrAl4SiO12 matrix in the temperature range, as well as the weakening of electron-phonon coupling with increasing temperature. The optimized phosphor was packaged with a blue chip into a NIR phosphor-converted light-emitting diode device. The light source device showed an output power of 119.02 mW and an electro-optical conversion efficiency of 11.02% under a driving current of 300 mA. The application potential of this NIR phosphor was demonstrated in the field of high-resolution nondestructive imaging.

Cr3+-Doped LiAlO2 NIR-I Emitting Phosphors with Superior Resistance to Thermal Quenching for Night Vision Monitoring and Bioimaging.

Near-infrared phosphor-converted light-emitting diodes (NIR pc-LEDs) as a new NIR light source has outstanding application potential in the fields of NIR spectroscopy analysis, sensing, imaging, and pattern recognition. Therefore, the development of NIR phosphors with good NIR luminescence thermal stability has attracted much attention. To this end, we developed LiAlO2:Cr3+ garnet-type NIR phosphors by a high-temperature solid-state reaction method. Under 405 nm excitation, the Cr3+ ions located in tetrahedrons of LiAlO2 emit NIR emission in a broadband NIR emission that covers 650-900 nm mixed with several sharp narrowband R-line emissions, which showed excellent luminescence thermal stability with integrated intensity of emission measured at 573 K is ∼90.86% of that measured at 303 K caused by good structural rigidity and low thermal expansion coefficient of the matrix material. An NIR pc-LED device assembled with the optimized LiAlO2:Cr3+ and a commercially available purple LED chip emitted NIR output power of ∼98.172 mW at a driving current of 300 mA and demonstrated an electro-optical conversion efficiency of ∼9.09%, while demonstrated it has excellent application potential in the fields of night vision monitoring and biomedical imaging.

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.

Ni2+ activated broadband near-infrared II germanate phosphor for pc-LED applications

The broadband near-infrared (NIR) pc-LED is considered as a new generation of light source for substance measurements based on NIR spectroscopy. The most studied Cr3+ doped broadband NIR phosphors emit in the near-infrared I region. However, there is a demand for broadband near-infrared II solid-state light sources for expanding the variety of detected substances. Herein, Ni2+ activated NIR II Mg14Ge5O24 phosphor is synthesized by high-temperature solid-state method. The phosphor shows a asymmetric broad NIR emission band peaked at 1420 nm, that is assigned to the 3T2(3F)→3A2(3F) transition of Ni2+. It is observed that the asymmetric emission band is contributed from two Ni2+ centers, Ni2+(I) and Ni2+(II), occupying Ge4+ site with the emission peaked at 1313 nm and Mg2+ site with the emission peaked at 1435 nm, respectively. It is found that the addition of Ti4+ and B3+ can significantly change the intensity ratio of the two Ni2+ centers and enhance the overall emission intensity. Moreover, the addition of Mn4+ results in only Ni2+(II) emission. The origin of the unique features mentioned above is discussed. The temperature dependence of the NIR emissions is also studied. Finally a broadband NIR II pc-LED with a moderate electro-optical conversion efficiency of 1.4 % is fabricated based on a 400 nm LED chip. The results indicate that the modified Mg14Ge5O24:Ni2+ is a potential broadband NIR II phosphor for pc-LED applications.

Electro-optical Q-switched laser array with one lamp pumping six Nd:YAG rods for programmable laser reconstruction in space-power-time domains

We report a novel laser array with one lamp pumping six Nd:YAG rods for programmable laser reconstruction in space-power-time domains. A sextuple ellipse pump cavity is proposed, and this scheme permits one xenon flash lamp with advantageously cylindrical pumping characteristics to simultaneously efficiently pump multiple Nd:YAG lasers in a laser system. The experimental setup was designed, and further experiments were carried out. The laser array can stably operate at a pumping rate of 1 Hz-10 Hz. Each laser beam of the six laser outputs has a divergence angle of less than 1.7 mrad, an output pulse of greater than 208 mJ, and a pulse width of approximately 10 ns, corresponding to a pulse peak power of approximately 20 MW. The laser array has a total output energy of 1.53 J at an electrical input of 93.3 J, corresponding to an overall electro-optical conversion efficiency of 1.64 % and an electro-optical slope efficiency of 3.17 %. Finally, laser array output pulses coded modulation in the space-power-time domains are achieved by electro-optical Q-switching. Therefore, the laser array provides the capability for programmable laser reconstruction in the space-power-time domains in a laser system for multipurpose applications, such as energy-tailored material processing, coded pulse laser ranging for improved signal-to-noise ratio (SNR), active optical remote sensing and scientific research.

Multi-junction cascaded vertical-cavity surface-emitting laser with a high power conversion efficiency of 74%

High electro-optical conversion efficiency is one of the most distinctive features of semiconductor lasers as compared to other types of lasers. Its further increase remains a significant objective. Further enhancing the efficiency of edge-emitting lasers (EEL), which represent the highest efficiency among semiconductor lasers at present, is challenging. The efficiency of vertical cavity surface emitting lasers (VCSELs) has always been relatively low compared to EEL. This paper, combining modeling with experiments, demonstrates the potential of multi-junction cascaded VCSELs to achieve high efficiency beyond that of EELs, our simulations show, that a 20-junction VCSEL can achieve an efficiency of more than 88% at room temperature. We fabricated VCSEL devices with different numbers of junctions and compared their energy efficiency. 15-junction VCSELs achieved a maximum efficiency of 74% at room temperature under nanosecond driving current, the corresponding differential quantum efficiency exceeds 1100%, being the largest electro-optical conversion efficiency and differential quantum efficiency reported until now for VCSELs.

Robust high-efficiency LuAG: Ce phosphor-in-silica glass (PiSG) for high-brightness laser lighting

Blue laser diodes (LDs), owing to their high electro-optical conversion efficiency, strong directivity, and small size under high power, have paved new paths in the semiconductor lighting and display industry. Blue LDs are expected to replace LED lighting in laser displays, automotive headlights, and other advanced lighting fields. In this study, the Lu3Al5O12: Ce3+ phosphor-in-silica glass (LuAG: Ce-PiSG) is fabricated using spark plasma sintering at 1060 °C. This method enables rapid sintering while maintaining the stability of the silica glass matrix, resulting in high transparency and minimal destruction of the crystal structure of the LuAG: Ce phosphor. The phosphor-converted LDs made from LuAG: Ce-PiSG exhibit high luminous efficacy (298 lm·W−1) and luminous flux (1069 lm). The results show that LuAG: Ce-PiSG has significant potential for application as a robust, high-efficiency phosphor conversion material for high-brightness laser lighting applications.

Research and Optimization Design of Thermal Management for LED

LED, a lighting source that has gained popularity in the 21st century, possesses characteristics such as energy efficiency, eco-friendliness, compactness, and durability. However, its electro-optical conversion efficiency remains relatively low, as approximately 80% to 90% of the input power is dissipated as thermal energy. Consequently, the temperature of the LED rises, leading to a decrease in its luminous efficiency. Hence, it is crucial to conduct research on efficient heat dissipation methods for LEDs. We have compiled research plans from various scientific institutions and observed that through optimized design, the heat dissipation capability of LEDs has significantly improved. This improvement has resulted in reduced thermal stress within the chips and packaging, ultimately enhancing their reliability.

Identification of intrinsic defects and hydrogen passivation in InP using hybrid functional

Indium phosphide is widely used in electronics and photovoltaic devices due to its high electro-optical conversion efficiency, high electron mobility, and good radiation resistance. Defects are the main limitation for the performance of InP devices. In this work, based on hybrid functional with finite size correction, electronic properties of intrinsic and H-related defects have been investigated in InP. We found that PIn defect is the most stable intrinsic defect with the lowest formation energy. Defect signals detected experimentally are defined by our calculated results. Experimentally observed electron traps with the energy level of EC − 0.66 eV and EC − 0.68 eV are ascribed to the transition level ɛ(−1/−2) and ɛ(−2/−3) of In vacancies. The hydrogenated vacancies in InP have been systematically reported in the present work. Formation energies of H-related defects indicate that hydrogen atoms prefer to bind to In vacancy than P vacancy. The formation energy of In vacancy decreases with the addition of H, while that of P vacancy increases. For hydrogenated In vacancies, it captures fewer electrons than bare In vacancies when the Fermi level is close to CBM. Especially for the VIn − 3H structure, it is 0 charge state in all Fermi levels so that it will not tend to capture electron or hole. Our work is helpful to explain experimental phenomena and radiation-induced damages and improve the performance of InP devices.

Doping profile architecture towards lower loss and higher efficiency for laser diodes.

A doping optimization model towards lower loss and higher efficiency at the target operating current is investigated. This model considers the effect of doping concentration on the series resistance and the internal loss. 780 nm lasers doped with a normal doping profile (Dop_normal) and an optimized doping profile (Dop_optimize) are both designed and fabricated. After doping optimization, the power loss decreased by 17%, the output power of the lasers increased by 26% and the electro-optical conversion efficiency increased by 22%. The model provides significant theoretical guidance for the optimization of the laser doping.

High–Power 792 nm Fiber–Coupled Semiconductor Laser

The pumping of Tm-doped crystal or fiber by a 792 nm semiconductor laser is an important way to generate a mid-infrared laser, which is widely used in various fields. In this paper, a high–power 792 nm fiber–coupled semiconductor laser module was successfully fabricated with the output power of 232 W at a 10 A continuous current and the electro-optic conversion efficiency of 48.6%. The laser module is coupled with 24 chips into a fiber by spatial multiplexing and polarization combination technology. For a single emitting laser chip, the continuous wave (CW) output power and threshold current are 10.45 W at 10 A and 1.55 A, respectively. A polarization as high as 94% can also be realized, which is more suitable for laser spatial beam combining. The laser module was aged for more than 4000 h at 12 A and 25 °C without obvious power degradation.

Mode-Modulation Structure Based on 650 nm Ridge Waveguide Edge-Emitting Laser

Traditional laser diodes operating at 650 nm are more prone to high-order mode excitation, resulting in poorer beam quality. In this paper, we designed GaInP–AlGaInP laser diodes (LD) with a 650 nm range and a trench mode-modulation structure based on the structure of edge-emitting laser (EEL) diodes. The effect of the three-trench structure was investigated theoretically and experimentally. The right trench structure laser chips demonstrated good beam quality while maintaining a high power output. An electro-optical conversion efficiency of 56% was demonstrated with a slope efficiency of 1.32 W/A at a 40 mA current. The maximum optical output power reached 40.8 mW.

High-efficiency spectral beam combining of an individual laser diode bar with polarization multiplexing.

In this Letter, a new strategy for the spectral beam combining (SBC) of an individual laser diode (LD) bar based on a polarization multiplexing external cavity is proposed and demonstrated. The maximum combining efficiency is up to 95.51%, which leads to an output power of 76.6 W and an electro-optic conversion efficiency of 48.33% under continuous wave operation at a current of 100 A. Compared to the conventional SBC, the combining efficiency, the output power, and the electro-optical conversion efficiency present improvements of 12%, 10W, and 6%, respectively. The results show that this novel SBC method is a prospective technique for increasing the combining efficiency of LD bars.

Study of Temperature Effects on the Design of Active Region for 808 nm High-Power Semiconductor Laser

High-power, broad-area, semiconductor lasers are attractive sources for material processing, aerospace, and laser pumping. The design of the active region is crucial to achieve the required high power and electro-optical conversion efficiency, since the temperature significantly affects the performance of the quantum well, including the internal quantum efficiency and mode gain. In this work, the temperature effects on the active region of a 808 nm high-power semiconductor laser were investigated theoretically and experimentally. The simulations were performed with a Quasi-3D model, which involved complete steady-state semiconductor and carrier confinement efficiency combined with a new mathematical method. The critical aluminum content of the quantum barrier was proposed and the relationship between temperature and various loss sources was disclosed in the temperature range of 213 to 333 K, which provides a reliable reference for the design of epitaxial structures of high-power semiconductor lasers in different operating conditions. Subsequently, the optimized epitaxial structure was determined and used to fabricate standard laser bar chips with a cavity length of 2 mm. The experimental electro-optical conversion efficiency of 71% was demonstrated with a slope efficiency of 1.34 W/A and an injection current of 600 A at the heatsink temperature of 223 K. A record high electro-optical conversion efficiency of 73.5% was reached at the injection current of 400 A, while the carrier confinement efficiency was as high as 98%.

Study of AlGaN-based deep ultraviolet laser diodes using one-way step-shaped quantum barriers and symmetrical step-shaped electron and hole blocking layers

To improve the carrier injection efficiency and optimize the performance of the AlGaN-based deep ultraviolet laser diodes (DUV-LDs), one-way step-shaped quantum barriers (OWS-QBs), a symmetrical step-shaped electron blocking layer (SS-EBL), and a symmetrical step-shaped hole blocking layer (SS-HBL) are proposed. Crosslight software is used to simulate the DUV-LDs with a traditional structure, with OWS-QBs, and with OWS-QBs, a SS-EBL, and a SS-HBL. The simulation results and physical mechanism analysis indicate that the SS-EBL, SS-HBL, and OWS-QBs contribute to the increased carrier concentration in the quantum wells, the reduced carrier leakage in the nonactive regions, the increased stimulated emission rate, the reduced threshold current and threshold voltage, and the enhanced output power and electro-optical conversion efficiency of DUV-LDs.

High-brightness and high-efficiency diode laser module based on double wavelength division multiplexing external cavities.

In this Letter, a new, to the best of our knowledge, external cavity structure based on double wavelength division multiplexing external cavities is proposed and demonstrated. The electro-optical conversion efficiency is improved and the brightness of the spectral beam combining diode lasers is enhanced. One wavelength division multiplexing external cavity is placed on the rear-side of the laser emitters to provide the strong optical feedback for wavelength locking and the other wavelength division multiplexing external cavity is placed on the front-side of laser emitters to combine three emitter beams to one beam. A maximum output power of up to 7.5 W is obtained and the brightness of the laser diode is 100 MW cm-2 sr-1 with an electro-optical conversion efficiency of 46.5%. Compared with a standard cavity for spectral beam combining, the use of double wavelength division multiplexing external cavities results in an electro-optical conversion efficiency improvement of 6.5%. The whole structure provides a new technology to achieve high-brightness and high electro-optical conversion efficiency for a laser diode source.

Composition-graded quantum barriers improve performance in AlGaN-based deep ultraviolet laser diodes

We propose two composition-graded quantum barriers (QBs) to improve the performance of AlGaN-based deep ultraviolet laser diodes (DUV-LDs). The optical and electrical properties of three LDs containing conventional QBs, graded increased QBs, and graded decreased QBs were numerically investigated. It was found that the LDs with graded decreased QBs significantly improved the carrier injection efficiency, raised the carrier concentration in the active region, reduced the carrier leakage, and enhanced the stimulated recombination rate of the LDs. Simulation results showed that, at an 80-mA injection current, the threshold current and threshold voltage were reduced to 29.5 mA and 4.78 V, respectively. The slope efficiency was improved to 2.52 W/A, and the electro-optical conversion efficiency was increased to 52.2%. Compared with the conventional structure of LDs, grading the QBs with decreasing Al-content improved the performance of the LD remarkably, which is essential for the development of DUV-LD.

Optimization of AlGaN-Based Deep Ultraviolet Laser Diodes with Graded Rectangular Superlattice Electron Blocking Layer and Graded Trapezoidal Superlattice Hole Blocking Layer

To improve the carrier confinement capability and optimize the performance of deep ultraviolet laser diodes (DUV-LDs), we propose the graded rectangular superlattice (GRSL) electron blocking layer (EBL) and the graded trapezoidal superlattice (GTSL) hole blocking layer (HBL) in this paper. Crosslight software is used to simulate and compare the DUV-LDs with rectangular superlattice (RSL) EBL and RSL HBL, GRSL EBL and GRSL HBL, and GRSL EBL and GTSL HBL. The simulation results indicate that GRSL EBL and GTSL HBL increase the carrier concentration in the quantum wells, reduce the electron leakage in the p-type region and the hole leakage in the n-type region, increase the radiation recombination rate, reduce the threshold voltage and threshold current, and increase the electro-optical conversion efficiency and output power of DUV-LDs more effectively.

电注入下的人工微结构模式调控激光研究进展

Electrically injected semiconductor lasers have several advantages over other lasers, such as high electro-optical conversion efficiency, small size, and long lifetime. Recently, the demand for semiconductor lasers has grown in several areas, including displays, material processing, medicine, communication, and other fields. Mode characteristics in lasers can directly modulate their performance, including the output power, beam quality, and spectrum linewidth. The performance of semiconductor lasers can be optimized by introducing artificial microstructures combined with mode control methods, including parity-time symmetry, bound states in the continuum, and compound cavity, which can expand relevant physical research and their commercial applications. In this paper, first, the objective of mode control is introduced. Then, the developments in electrically injected semiconductor lasers, including domestic and international research studies, physical principles, and corresponding applications, are reviewed. Finally, conclusions and future outlooks are discussed.

A High Precision and Multifunctional Electro-Optical Conversion Efficiency Measurement System for Metamaterial-Based Thermal Emitters.

In this study, a multifunctional high-vacuum system was established to measure the electro-optical conversion efficiency of metamaterial-based thermal emitters with built-in heaters. The system is composed of an environmental control module, an electro-optical conversion measurement module, and a system control module. The system can provide air, argon, high vacuum, and other conventional testing environments, combined with humidity control. The test chamber and sample holder are carefully designed to minimize heat transfer through thermal conduction and convection. The optical power measurements are realized using the combination of a water-cooled KBr flange, an integrating sphere, and thermopile detectors. This structure is very stable and can detect light emission at the μW level. The system can synchronously detect the heating voltage, heating current, optical power, sample temperatures (both top and bottom), ambient pressure, humidity, and other environmental parameters. The comprehensive parameter detection capability enables the system to monitor subtle sample changes and perform failure mechanism analysis with the aid of offline material analysis using scanning electron microscopy, energy dispersive X-ray spectroscopy, and X-ray diffraction. Furthermore, the system can be used for fatigue and high-low temperature impact tests.