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Thermally activated delayed fluorescence (TADF)‐based materials are attracting widespread attention for different applications owing to their ability of harvesting both singlet and triplet excitons without noble metals in their structures. As compared to the conventional fluorescence and room‐temperature phosphorescence pathways, TADF originates from the reverse intersystem crossing process from the excited triplet state (T1) to the singlet state (S1). Therefore, TADF emitters enabling activated and long lifetime T1 excitons are potential candidates for generating long‐lived afterglow emission, an effect that can still be observed for a while by the naked eye after the removal of the excitation light source. Recently, TADF‐based organic afterglow materials featuring high photoluminescence quantum yields and long lifetimes above 100 ms under ambient conditions, have emerged for advanced information security, high‐contrast biological imaging, optoelectronic devices, and intelligent sensors, whereas the related systematic review is still lacking. Herein, the recent progress in TADF‐based organic afterglow materials is summarized and an overview of the photophysical mechanism, design strategies, and the performances for relevant applications is given. In addition, the challenge and perspective of this area are given at the end of the review. [ABSTRACT FROM AUTHOR]

High-definition near-eye display technology has extremely close sight distance, placing a higher demand on the size, performance, and array of light-emitting pixel devices. Based on the excellent photoelectric performance of metal halide perovskite materials, perovskite light-emitting diodes (PeLEDs) have high photoelectric conversion efficiency, adjustable emission spectra, and excellent charge transfer characteristics, demonstrating great prospects as next-generation light sources. Despite their potential, the solubility of perovskite in photoresist presents a hurdle for conventional micro/nano processing techniques, resulting in device sizes typically exceeding 50 μm. This limitation impedes the further downsizing of perovskite-based components. Herein, we propose a plane-structured PeLED device that can achieve microscale light-emitting diodes with a single pixel device size < 2 μm and a luminescence lifetime of approximately 3 s. This is accomplished by fabricating a patterned substrate and regulating ion distribution in the perovskite through self-doping effects to form a PN junction. This breakthrough overcomes the technical challenge of perovskite–photoresist incompatibility, which has hindered the development of perovskite materials in micro/nano optoelectronic devices. The strides made in this study open up promising avenues for the advancement of PeLEDs within the realm of micro/nano optoelectronic devices. [ABSTRACT FROM AUTHOR]

Silicon is indisputably the most advanced material for scalable electronics, but it is a poor choice as a light source for photonic applications, due to its indirect band gap. The recently developed hexagonal Si1−xGex semiconductor features a direct bandgap at least for x > 0.65, and the realization of quantum heterostructures would unlock new opportunities for advanced optoelectronic devices based on the SiGe system. Here, we demonstrate the synthesis and characterization of direct bandgap quantum wells realized in the hexagonal Si1−xGex system. Photoluminescence experiments on hex-Ge/Si0.2Ge0.8 quantum wells demonstrate quantum confinement in the hex-Ge segment with type-I band alignment, showing light emission up to room temperature. Moreover, the tuning range of the quantum well emission energy can be extended using hexagonal Si1−xGex/Si1−yGey quantum wells with additional Si in the well. These experimental findings are supported with ab initio bandstructure calculations. A direct bandgap with type-I band alignment is pivotal for the development of novel low-dimensional light emitting devices based on hexagonal Si1−xGex alloys, which have been out of reach for this material system until now. Authors demonstrate the synthesis and characterization of direct bandgap quantum wells in the hexagonal Si1−xGex system. Photoluminescence experiments show light emission up to room temperature, and the emission wavelength can be tuned by thickness of the wells and the Si composition. [ABSTRACT FROM AUTHOR]

Optoelectronic and spinoptronic technologies benefit from flexible and tunable coherent light sources combining the best properties of nano- and material-engineering to achieve favorable properties such as chiral lasing and low threshold nonlinearities. In this work we demonstrate an electrically wavelength- and polarization-tunable room temperature polariton laser due to emerging photonic spin–orbit coupling. For this purpose, we design an optical cavity filled with both birefringent nematic liquid crystal and an inorganic perovskite. Our versatile growth method of single CsPbBr3 inorganic perovskite crystals in polymer templates allows us to reach strong light–matter coupling and pump-induced condensation of exciton–polaritons resulting in coherent emission of light. The sensitivity of the liquid crystal to external voltage permits electrical tuning of the condensate energy across 7 nm; its threshold power, allowing us to electrically switch it on and off; and its state of polarization sweeping from linear to locally tilted circularly polarized emission. [ABSTRACT FROM AUTHOR]

Plasmonic modes confined to metallic nanostructures at the atomic and molecular scale push the boundaries of light–matter interactions. Within these extreme plasmonic structures of ultrathin nanogaps, coupled nanoparticles, and tunnelling junctions, new physical phenomena arise when plasmon resonances couple to electronic, exitonic, or vibrational excitations, as well as the efficient generation of non-radiative hot carriers. This review surveys the latest experimental and theoretical advances in the regime of extreme nano-plasmonics, with an emphasis on plasmon-induced hot carriers, strong coupling effects, and electrically driven processes at the molecular scale. We will also highlight related nanophotonic and optoelectronic applications including plasmon-enhanced molecular light sources, photocatalysis, photodetection, and strong coupling with low dimensional materials. [ABSTRACT FROM AUTHOR]

Future displays need to be stretchable, bendable, and wearable to match consumers' needs for convenience, portable equipment, and real‐time information display. The development of flexible light source components, like flexible light‐emitting diodes (LEDs), is urgently required to fulfill these needs. Metal halide perovskites, known for their excellent optoelectronic properties and ductility, are considered the most promising light‐emitting materials for high‐definition displays, and their outstanding advantage is that the metal halide perovskites would be achieved by solution process under low temperature (<150 °C), which is especially good for the flexible organic substrates to maintain high conductivity during fabrication of flexible LEDs. In recent years, flexible perovskite LEDs have made significant progress, but still face a great deal of difficulties, obstacles, and great challenges. Herein, the mechanical properties of perovskite materials are examined and the failures for perovskite‐based flexible optoelectronic devices under strain are discussed. The authors then focus on optimizing each functional layer and the recent advancement in flexible perovskite LEDs is summarized. Finally, a brief outlook on the challenges faced by flexible perovskite LEDs and their possible future development is provided. [ABSTRACT FROM AUTHOR]

The development of flexible optoelectronic devices has led to the appearance of new applications, ranging from wearable displays to medical implants. Hence, strategies have been developed to make flexible every component of the devices, including the light-emitting part. One such approach relies on the use of micro- or nano-light emitting diodes (LEDs) for their reduced footprint, allowing them to be easily separated from their substrate and embedded in a flexible matrix. In this review, the authors provide a comparison between the different geometries obtained by the growth of III-nitride structures for the fabrication of flexible devices. The processes used for their fabrication are then presented in detail. Last, an overview of the state of the art regarding flexible nanowire-based LED is provided, as well as some perspectives regarding their improvement. [ABSTRACT FROM AUTHOR]

The development of highly efficient active integrated photonic circuits is crucial for advancing information and computing science. Lead halide perovskite semiconductors, with their exceptional optoelectronic properties, offer a promising platform for such devices. In this study, active micro multifunctional photonic devices were fabricated on monocrystalline CsPbBr3 perovskite thin films using a top-down etching technique with focused ion beams. The etched microwire exhibited a high-quality micro laser that could serve as a light source for integrated devices, facilitating angle-dependent effective propagation between coupled perovskite-microwire waveguides. Employing this strategy, multiple perovskite-based active integrated photonic devices were realized for the first time. These devices included a micro beam splitter that coherently separated lasing signals, an X-coupler performing transfer matrix functions with two distinguishable light sources, and a Mach-Zehnder interferometer manipulating the splitting and coalescence of coherent light beams. These results provide a proof-of-concept for active integrated functionalized photonic devices based on perovskite semiconductors, representing a promising avenue for practical applications in integrated optical chips. Researchers showcase an integrated photonic device with monocrystalline CsPbBr3 perovskite. Employing top-down etching approach, it introduces for micro lasers, beam splitters, X-couplers, Mach-Zehnder interferometers on perovskite films. This opens avenues for integrating perovskite semiconductors into optical chips, promising advancements in information and computing science. [ABSTRACT FROM AUTHOR]

Highly emissive ternary Eu(III) complexes were synthesized with a tri-fluorinated β-diketone as principal ligand and heterocyclic aromatic compounds as ancillary ligands to assess their utility as an illuminating material for display devices and other optoelectronics. The general characterizations, regarding the coordinating facets of complexes were accomplished via various spectroscopic techniques. Thermal stability was investigated via TGA/DTA. Photophysical analysis was accomplished by PL studies, Band gap value, color parameters and J-O analysis. DFT calculations were performed adopting geometrically optimized structure of complexes. Superb thermal stability has been achieved in complexes, which decides their concrete candidature for display devices. The bright red luminescence of complexes is ascribed to 5D0 → 7F2 transition of Eu(III) ion. Colorimetric parameters unlocked the applicability of complexes as warm light source and J-O parameters adequately summarized the coordinating surrounding around the metal ion. Various radiative properties were also evaluated which suggested the prospective use of complexes in lasers and other optoelectronic devices. The band gap and Urbach band tail, procured from absorption spectra, revealed the semiconducting behavior of synthesized complexes. DFT studies rendered the energies of FMO and various other molecular parameters. It can be summarized from the photophysical and optical analysis of synthesized complexes that these complexes are virtuous luminescent materials and possess potentiality to be used in diverse domain of display devices. [ABSTRACT FROM AUTHOR]

Colloidal quantum dot (CQD) lasers show promising applications in flexible optoelectronic devices, due to their tunable emission wavelength, narrow spectrum bandwidth and high power intensity. However, fabricating a flexible CQD laser is challenging because of the difficulties in fabricating optical cavities on flexible substrates using traditional microfabrication technologies. Herein, we propose a one-step self-assembly approach to fabricate flexible CQD supraparticle lasers. The whole assembly approach is processed in a liquid environment without surfactants, and the formed spherical CQD supraparticles are featured with smooth surfaces, serving as high-quality-factor whispering-gallery mode cavities to support laser oscillation. A low lasing threshold of 54 µJ/cm2 is observed while exciting a CQD supraparticle with pulsed femtosecond lasers. The calculated cavity quality factor of 963 for CQD supraparticle lasers is twofold larger than that of CQD lasers assembled with surfactants. Moreover, the CQD supraparticles can serve as free-standing lasers, which allows them to be deposited on flexible substrates such as paper and cloth. Furthermore, our CQD lasers show high stability, after being continuously photoexcited above the threshold for 400 min, their lasing intensity remains at 85.7% of the initial value. As bright, free-standing and long-term stable light sources, the assembled CQD lasers proposed in this work show potential applications in wearable devices and medical diagnosis. [ABSTRACT FROM AUTHOR]

Traditional light sources cannot emit an electromagnetic (EM) field with an orbital angular momentum (OAM), limiting their applications in modern optics. The recent development of the OAM laser, mainly based on micro- and nanostructures, can satisfy the increasing requirements for on-chip photonics and information capacities. Nevertheless, the photonic structures have fixed parameters that prevent these OAM lasers from being dynamically tuned. Here, we propose tunable vortex lasing from a microring cavity integrated by a phase change material, Ge2Sb2Te5 (GST225). By modulating the complex refractive index to create an exceptional point (EP) to break the degeneracy of whispering gallery modes with opposite orientations, the microlaser working at the EP can impart an artificial angular momentum, thus emitting vortex beams with well-defined OAM. The grating scatter on the edge of the microring can provide efficient vertical radiation. The vortex laser wavelength from the GST225/InGaAsP dual-layered microring cavity can be dynamically tuned by switching the state of GST225 between amorphous and crystalline without changing the microring geometry. We construct an electric-thermal model to show the tuning range of operating wavelengths (EPs) from 1544.5 to 1565.9 nm in ~25 ns. Our study on high-speed tunable PT-symmetry vortex lasers facilitates the next generation of integrated optoelectronic devices for optical computing and communications in both classical and quantum regions. [ABSTRACT FROM AUTHOR]

Chiral halide perovskites have emerged as promising circularly polarized light sources due to their great potential applications in 3D displays, optical data storage, and optical communication devices. However, to date, chiral halide perovskites with efficient blue circularly polarized luminescence (CPL) are scarcely unearthed. Herein, through formamidine engineering to decrease lattice distortion, the first new types of chiral corrugated 2D halide perovskites are presented (R/S)‐(BPEA)FAPbBr4·H2O (2‐R/S) (BPEA = 4‐bromophenylethylaminium, FA = formamidinium). Interestingly, driven by the incorporation of FA organic cations, the chiral perovskite layer realizes the transformation from (100)‐oriented (R/S)‐(BPEA)2PbBr4·H2O (1‐R/S) to (110)‐oriented 2‐R/S accompanying with reduced lattice distortion. More importantly, (110)‐oriented chiral perovskites 2‐R exhibit remarkable blue CPL with large asymmetry factors (glum =8.4 × 10−3). This work offers an exciting approach to realizing efficient blue CPL and promotes their further applications in photoelectronic devices. [ABSTRACT FROM AUTHOR]

High-speed light emitters integrated on silicon chips can enable novel architectures for silicon-based optoelectronics, such as on-chip optical interconnects and silicon photonics. However, conventional light sources based on compound semiconductors face major challenges for their integration with the silicon-based platforms because of the difficulty of their direct growth on a silicon substrate. Here, we report high-speed, ultra-small-size on-chip electroluminescence (EL) emitters based on semiconducting single-walled carbon nanotube (SWNT) thin films. The peaks of the EL emission spectra are about 0.15-eV redshifted from the peaks of the absorption and photoluminescence emission spectra, which probably suggest emission from trions. High-speed responses of ∼100 ps were experimentally observed from the EL emitters, which indicate the possibility of several-GHz modulation. The pulsed light generation was also obtained by applying the pulse voltage. These high-speed and ultra-small-size EL emitters can enable novel on-chip optoelectronic devices for highly integrated optoelectronics and silicon photonics. [ABSTRACT FROM AUTHOR]

The nonlinear optical (NLO) response of photonic materials plays an important role in the understanding of light–matter interaction as well as pointing out a diversity of photonic and optoelectronic applications. Among the recently studied materials, 2D-LTMDs (bi-dimensional layered transition metal dichalcogenides) have appeared as a beyond-graphene nanomaterial with semiconducting and metallic optical properties. In this article, we review most of our work in studies of the NLO response of a series of 2D-LTMDs nanomaterials in suspension, using six different NLO techniques, namely hyper Rayleigh scattering, Z-scan, photoacoustic Z-scan, optical Kerr gate, and spatial self-phase modulation, besides the Fourier transform nonlinear optics technique, to infer the nonlinear optical response of semiconducting MoS2, MoSe2, MoTe2, WS2, semimetallic WTe2, ZrTe2, and metallic NbS2 and NbSe2. The nonlinear optical response from a thermal to non-thermal origin was studied, and the nonlinear refraction index and nonlinear absorption coefficient, where present, were measured. Theoretical support was given to explain the origin of the nonlinear responses, which is very dependent on the spectro-temporal regime of the optical source employed in the studies. [ABSTRACT FROM AUTHOR]

In recent years, with the rapid development of military, optical communication, biological imaging, and other fields, practical engineering applications such as fiber‐optic gyroscope, wavelength division multiplexing, and optical coherence tomography have put forward higher requirements on light sources. Amplified spontaneous emission (ASE) light source has become an excellent candidate due to its advantages such as suitable bandwidth, low coherence, and high power. Although the ASE light source is developed to a certain extent, there is still great room for improvement in the choice of gain medium and device structure. In order to accelerate the development and practical engineering application of ASE optoelectronic devices, it is of great significance to grasp the basic characteristics of the gain materials and the design of the device structure. In this review, the principle of the ASE effect and its difference with the generation of lasing are analyzed. Then, the optical gain properties of various gain materials, together with different structural types of electrically pumped ASE devices and their practical engineering applications, are summarized. Finally, the new ASE light‐emitting devices integrated with high‐gain materials and low‐cost structures are prospected to provide more ideas for their development. [ABSTRACT FROM AUTHOR]

Silicon photonics is the core technology in the post-Moore ’ s era, characterized by the deep integration of optoelectronics and microelectronics. Silicon photonics can leverage the existing complementary metal-oxide-semiconductor (CMOS) infrastructure to fabricate low power consumption, high integration density, fast transmission speed, and highreliability silicon photonic chips which are widely employed in data centers and communication systems. At present, most optoelectronic devices like Si-based photodetectors and Si-based optical modulators have realized on-chip integration except for the Si-based lasers as essential light sources. The directly epitaxial III-V materials on silicon substrates is recognized as one of the most promising solutions to achieve low-cost and large-size monolithic integration of Si-based lasers, still facing many significant challenges. In this paper, the research progress of Si-based light sources is presented from the aspects of directly epitaxial on-axis III-V/ Si (001) substrates, on-axis Si-based laser materials, epitaxy technology and monolithic integration at first. Then the achievements in Si-based directly epitaxial quantum well lasers and quantum dot lasers in our group are reported in detail, including the growth of antiphase domains-free GaAs/ Si (001) substrates, epitaxial materials of InGaAs/ AlGaAs quantum well lasers and InAs/ GaAs quantum dot lasers, and fabrication of novel coplanar electrode structures of silicon photonic chips in parallel mode. [ABSTRACT FROM AUTHOR]

Near-infrared luminescence phosphors are key material basis to potential applications for light sources and optoelectronic devices. In particular, it is vital to tune the luminescent properties of these phosphors in a flexible and controllable manner. Here, we demonstrate that a flexural strain originated from bending can be used to modulate the photoluminescence of freestanding Ni2+ doped SrTiO3 membranes. The bent membranes show remarkable red-shift emissions, arising from the variations of the symmetry of host materials and the local crystal fields around the Ni2+ ions. In addition, the phosphor films show a reversible and stable wavelength modulation with remarkable anti-fatigue characteristics after 104 bending cycles. These results provide a potential routine to develop flexible strain-tunable devices for applications in optical amplifiers and other optoelectronics. [ABSTRACT FROM AUTHOR]

The interaction of light with the bipolar characteristics of two-terminal devices synthesized with ZnO film is investigated. Three types of devices are built. The first set consisted of devices with n-ZnO film on SiO2/Si or sapphire substrate. The second set is a vertical p–n junction with n-ZnO film on p-SrCu2O2 film on p-Si substrate. The third set is like the second but with a film of ZnO nanorods placed between the n- and p-layers. The bottom electrode is either a metal film on the Si substrate or the p-Si substrate with low resistance. The top electrode consisted of either a tungsten or Ag coated Au wire tip. The changes in the bipolar characteristics are explained in terms of the control of the mobility of the Vo++ defects present in ZnO film by the incidence of radiation either from the internal or external source of light. The external source is from the room light or from a lamp. The internal source is from the defect-induced radiation from the p–n junction. The present work illustrates that optical illumination of memristor device with transparent semiconducting oxides modulates the switching characteristics, thus providing an opportunity for improving the number of device states. The results also illustrate that optical modulation of bipolar characteristics is more significant in the p–n junction devices emphasizing the benefits of processing of optoelectronic devices with transparent semiconducting oxides. [ABSTRACT FROM AUTHOR]

GaN-based microring lasers grown on Si are promising candidates for compact and efficient light sources in Si-based optoelectronic integration and optical interconnect due to their small footprints, low mode volume, low power consumption, and high modulation rate. However, the high symmetry of circular microcavity leads to isotropic emission, which not only reduces the light collection efficiency, but also affects other adjacent devices during data transmission. In this study, the unidirectional lasing emission of room-temperature current-injected GaN-based microring laser was realized by coating metal Ag on the microring sidewall and integrating a direct coupled waveguide. The light was efficaciously confined in the cavity and only emitted from the waveguide, which avoided optical signal crosstalk with other adjacent devices. Furthermore, we integrated a microdisk at the other end of the waveguide as a photodetector, which could effectively detect the output power of the microring laser from the direct coupled waveguide. Therefore, a preliminary on-chip integration of GaN-based microring laser, waveguide and photodetector on Si substrate was successfully demonstrated for the first time, opening up a new way for on-chip integration and optical interconnect on a GaN-on-Si platform. [ABSTRACT FROM AUTHOR]

Lead halide perovskites are attractive light source candidates for new amplifiers and lasers in the growing field of short‐distance data communication. However, the presence of plenty of defects and poor stability are the major obstacle to the production and application of perovskite optoelectronic devices. Three strategies are proposed to prepare MAPbI3 perovskite films with high stability and enhanced light amplification in this study: 1) MAPbI3 films are prepared with ionic liquid methylammonium acetate (MAAc) to improve the quality of the films; 2) a poly(methyl methacrylate) (PMMA) passivation layer is used to improve the optical and thermal stability of the MAPbI3 film; 3) a symmetric waveguide (SWG) structure is designed to enhance the amplified spontaneous emission (ASE) properties of the MAPbI3 film. The formed SWG exhibits increased mode confinement and reduced propagation loss, thus enabling a lower ASE threshold, a higher optical gain and improved photostability, thermal and humidity stability compared with the pristine MAPbI3 film. Femtosecond transient absorption spectroscopy and electric field distribution calculation are utilized to elucidate the carrier dynamics and carrier‐phonon effect and the microscopic origin of the observed effects of functionalization. This study indicates the possibility of simple and effective approaches for realizing efficient ASE and lasing. [ABSTRACT FROM AUTHOR]

The Sn-doped CuS nanostructures with different Sn-doping concentrations (Sn 1 (5 %), Sn 2 (10 %), and Sn 3 (15 %)) were synthesized by the sonochemical method. Due to the difference in ionic radii between Cu and Sn, the stress in the CuS crystal was increased from 41 × 10−4 for the undoped sample to 50 × 10−4 for the Sn 2 -doped sample. The absorption of visible light by the doped samples was increased dramatically. The morphology of CuS nanostructures was changed from nanoparticles (NPs) in the undoped CuS to nanoplates in the Sn 2 -doped CuS. Finally, the optoelectronic applications of the samples were studied, and it was shown that all the samples responded to the visible light source, and their resistance was decreased due to light radiation. The results indicated that specific detectivity (D*), responsivity (R), and sensitivity (S) as the figure-of-merit (FOM) of the photodetectors were increased from 2.07 × 109 Jones, 0.92 mA W⁻1, and 1328 % for undoped CuS nanostructures to 65.22 × 109 Jones, 28.27 mA W⁻1, and 3802 % for the Sn 2 -doped CuS nanostructures. The Mott-Schottky (M − S) results indicated that a higher acceptor carrier concentration in the Sn-doped CuS compared to undoped CuS was one of the most critical factors in enhancing the FOM of the photodetectors fabricated with Sn-doped CuS nanostructures. [Display omitted] • Sn-Doped CuS nanostructures have been synthesized by the sonochemical method. • Figure-of-merit of the photodetectors based CuS nanostructures has been improved by Sn-doping. • Defect concentrations in the CuS nanostructures have been increased by Sn-doping. [ABSTRACT FROM AUTHOR]

Featured Application: Silicon photonics. In recent years, silicon photonics has achieved great success in optical communication area. More and more on-chip optoelectronic devices have been realized and commercialized on silicon photonics platform, such as silicon-based modulators, filters and detectors. However, on-chip light sources are still not achieved because that silicon is an indirect bandgap material. To solve this problem, the rare earth element erbium (Er) is considered, which emits light covering 1.5 μm to 1.6 μm and has been widely used in fiber amplifiers. Compared to Er-doped fiber amplifiers (EDFA), the Er ion concentration needs to be more than two orders higher for on-chip Er-based light sources due to the compact size integration requirements. Therefore, the choice of the host material is crucially important. In this paper, we review the recent progress in on-chip Er-based light sources and the advantages and disadvantages of different host materials are compared and analyzed. Finally, the existing challenges and development directions of the on-chip Er-based light sources are discussed. [ABSTRACT FROM AUTHOR]

Six green glowing terbium (III) complexes were fabricated via grinding method utilizing a prime organic ligand (L) and nitrogen donor ancillary ligands. Characterization of synthesized complexes was accomplished through various spectroscopic techniques. The significant thermal stability was determined by thermogravimetric analysis while the energy bandgap and Urbach energy were investigated through diffused reflectance spectra of these complexes. The peak observed at 548 nm in emission spectra is responsible for the virescent color of these complexes. Color purity, decay time, quantum yield, and emission intensities of ternary complexes were significantly improved as compared to binary ones due to the synergistic effect of ancillary ligands. Judd–Ofelt parameters were determined by the NIR absorption spectrum, which claims the asymmetric environment around the terbium (III) ion. CCT values advocate the applicability of these complexes in green light-emitting materials as a cool light source. The biological assignments reveal the significance of these complexes as potent antioxidants and antimicrobial agents. The energy transfer process highlights the enhancement of luminescence in these complexes via the synergic effect of ligands. Our investigation portrays that these complexes can be employed in laser technology, display devices, semiconductors, biological fields, and optoelectronic devices. [ABSTRACT FROM AUTHOR]

Silica fibers are nowadays cornerstones in several technological implementations from long‐distance communication, to sensing applications in many scenarios. To further enlarge the functionalities, the compactness, and the performances of fiber‐based devices, one needs to reliably integrate small‐footprint components such as sensors, light sources, and detectors onto single optical fiber substrates. Here, a novel proof of concept is presented to deterministically integrate optoelectronic chips onto the facet of an optical fiber, further implementing the electrical contacting between the chip and fiber itself. The CMOS‐compatible procedure is based on a suitable combination of metal deposition, laser machining, and micromanipulation, directly applied onto the fiber tip. The proposed method is validated by transferring, aligning, and bonding a quantum‐well based laser on the core of a multimode optical fiber. The successful monolithic device integration on fiber shows simultaneously electrical contacting between the laser and the ferrule, and 20% light in‐coupling in the fiber. These results pave new ways to develop the next generation of optoelectronic systems on fiber. The technological approach will set a new relevant milestone along the lab‐on‐fiber roadmap, opening new avenues for a novel class of integrated optoelectronic fiber platforms, featuring unrivaled miniaturization, compactness, and performances levels, designed for specific applications. [ABSTRACT FROM AUTHOR]

This research develops a three degrees of freedom (DOF) measurement system by integrating Fabry-Perot interferometer and photoelectronic inspection module to determine linear displacement, horizontal and vertical straightness geometric error parameters simultaneously. The interferometer and the photoelectronic inspection module in a three DOF measurement system share the same light source, and the two structures are used to measure linear displacement and straightness errors. The experimental results are utilized to calculate the relevant error parameters according to ISO standards and numerical analysis. They show that after the machine error compensation, the positioning deviation of the system is reduced from 55 μm to 19 μm, corresponding to the reduction of 65%. The accuracy is promoted from 65 μm to 31 μm, about the improvement of 52%. The horizontal and vertical straightness errors of the machine are 4.30 μm and 5.71 μm respectively. [ABSTRACT FROM AUTHOR]

Thin-film microscale light-emitting diodes (LEDs) are efficient light sources and their integrated applications offer robust capabilities and potential strategies in biomedical science. By leveraging innovations in the design of optoelectronic semiconductor structures, advanced fabrication techniques, biocompatible encapsulation, remote control circuits, wireless power supply strategies, etc., these emerging applications provide implantable probes that differ from conventional tethering techniques such as optical fibers. This review introduces the recent advancements of thin-film microscale LEDs for biomedical applications, covering the device lift-off and transfer printing fabrication processes and the representative biomedical applications for light stimulation, therapy, and photometric biosensing. Wireless power delivery systems have been outlined and discussed to facilitate the operation of implantable probes. With such wireless, battery-free, and minimally invasive implantable light-source probes, these biomedical applications offer excellent opportunities and instruments for both biomedical sciences research and clinical diagnosis and therapy. [ABSTRACT FROM AUTHOR]

• High fluorescence thermal stability carbon dots for photoluminescence and lasing up to 1000 K are realized by multi-core@shell double confinement. • PL intensity of CDs@SiO 2 remains unchanged at 1000 K compared with that at room temperature and retains 92% of the original value after heating at 800 K for 4 h. • High-temperature speckle-free laser imaging is achieved at 800 K by using CDs@SiO 2 lasers as light sources. Low thermal stability has been a common challenge for fluorescent nano-materials in high-power optoelectronic devices or high-temperature environment. In this paper, a double-confined strategy, which is conducted to giant enhancement of thermal stability, is designed for carbon dots (CDs) to form CDs@SiO 2 multi-core@shell structure. This structure can not only prevent CDs from thermal quenching of photoluminescence (PL) up to 1000 K, but also even achieve lasing at such a high temperature without gas protection, indicating the excellent protection of SiO 2 multi-core@shell structure to resist the thermal quenching on one hand, while on the other hand enhance the PL and meanwhile stabilize the luminescence center of CDs. Hence, the CDs@SiO 2 could find a potential application in high-temperature speckle-free laser imaging by using CDs random laser as light source. This research is a major step toward the application of fluorescence materials at high temperature, and meanwhile provides the novel compass to construction of thermally stable fluorescence materials and even laser gain mediums, which could be expected to make a great impact in the area of thermal damage monitoring, manufacturing and aerospace etc. [ABSTRACT FROM AUTHOR]

2D materials show wide‐ranging physical properties with their electronic bandgaps varying from zero to several electronvolts, offering a rich platform to explore novel electronic and optoelectronic functions. Notably, atomically thin 2D materials are well suited for integration in optoelectronic circuits, because of their ultrathin body, strong light–matter interactions, and compatibility with the current silicon photonic technology. In this paper, an overview of the state of the art of using 2D materials in optoelectronic devices and integration is provided. The optoelectronic properties of 2D materials and their typical electronic and optoelectronic applications including light sources, optical modulators, photodetectors, field‐effect transistors, and logic circuits are summarized. The device configurations, operation mechanisms, and device figures‐of‐merit are introduced and discussed. By discussing the recent advances, future trends, and existing challenges of 2D materials and their optoelectronic devices, this review has provided an insight into the perspectives of 2D materials for optoelectronic integration and may guide the development of this field within the research community. [ABSTRACT FROM AUTHOR]

Finesse coefficient is one of the most important parameters describing the properties of a resonant cavity. In this research, a mathematical investigation of the application of diamond structures in a fiber-optic Fabry–Perot measurement head to assess their impact on the finesse coefficient is proposed. We present modeled transmission functions of cavities utilizing a nitrogen-doped diamond, a boron-doped diamond, nanocrystalline diamond sheet and a silver mirror. The diamond structures were deposited using a microwave plasma-assisted chemical vapor deposition system. A SEM investigation of surface morphology was conducted. The modeling took into consideration the fiber-optic Fabry–Perot setup working in a reflective mode, with an external cavity and a light source of 1550 nm. A comparison of the mathematical investigation and experimental results is presented. [ABSTRACT FROM AUTHOR]

As contemporary star materials, 2D monolayer semiconductors have drawn huge research interests owing to their striking electrical and optical properties, rendering them ideal candidates as building blocks for novel optoelectronic devices. Towards light emitting devices with extended functions, it is necessary to manipulate the polarization of light emission from monolayer semiconductors. However, most of these monolayer semiconductors exhibit no or very limited polarization sensitivity inherited from their structural anisotropy, making it challenging to develop highly polarized light sources. Herein, by embedding monolayer tungsten diselenide (WSe2) in a nanowire‐on‐film nanocavity, highly polarized light emission is demonstrated, featuring degree of polarization (DoP) of ≈99%. The highly anisotropic light emission originates from the near‐field coupling between the WSe2 monolayer with the polarization‐dependent gap plasmons of the nanowire‐on‐film nanocavity. Moreover, as the width of the nanowire essentially defines the gap‐plasmon resonance of the nanowire‐on‐film nanocavity, the anisotropy of the highly polarized light emission is systematically tuned by changing the nanowire width. The findings pave the way for engineering anisotropic optical properties of monolayer semiconductors and will boost the development of functional polarization‐sensitive 2D optoelectronic devices. [ABSTRACT FROM AUTHOR]

While vat photopolymerization has many advantages over soft lithography in fabricating microfluidic devices, including efficiency and shape complexity, it has difficulty achieving well-controlled micrometer-sized (smaller than 100 μm) channels in the layer building direction. The considerable light penetration depth of transparent resin leads to over-curing that inevitably cures the residual resin inside flow channels, causing clogs. In this paper, a 3D printing process — in-situ transfer vat photopolymerization is reported to solve this critical over-curing issue in fabricating microfluidic devices. We demonstrate microchannels with high Z-resolution (within 10 μm level) and high accuracy (within 2 μm level) using a general method with no requirements on liquid resins such as reduced transparency nor leads to a reduced fabrication speed. Compared with all other vat photopolymerization-based techniques specialized for microfluidic channel fabrication, our universal approach is compatible with commonly used 405 nm light sources and commercial photocurable resins. The process has been verified by multifunctional devices, including 3D serpentine microfluidic channels, microfluidic valves, and particle sorting devices. This work solves a critical barrier in 3D printing microfluidic channels using the high-speed vat photopolymerization process and broadens the material options. It also significantly advances vat photopolymerization's use in applications requiring small gaps with high accuracy in the Z-direction. Despite many advantages of vat photopolymerization in microfluidic device fabrication, well-controlled μm-sized (< 100 μm) channels in the layer building direction remains a challenge. Here, authors present a general high resolution and low-cost 3D printing process that can produce devices within the 10 μm scale. [ABSTRACT FROM AUTHOR]

III‐V semiconductor nanowires with quantum wells (QWs) are promising for ultra‐compact light sources and photodetectors from visible to infrared spectral region. However, most of the reported InGaAs/InP QW nanowires are based on the wurtzite phase and exhibit non‐uniform morphology due to the complex heterostructure growth, making it challenging to incorporate multiple‐QWs (MQW) for optoelectronic applications. Here, a new strategy for the growth of InGaAs/InP MQW nanowire arrays by selective area metalorganic vapor phase epitaxy is reported. It is revealed that {110} faceted InP nanowires with mixed zincblende and wurtzite phases can be achieved, forming a critical base for the subsequent growth of highly‐uniform, taper‐free, hexagonal‐shaped MQW nanowire arrays with excellent optical properties. Room‐temperature lasing at the wavelength of ≈1 µm under optical pumping is achieved with a low threshold. By incorporating dopants to form an n+‐i‐n+ structure, InGaAs/InP 40‐QW nanowire array photodetectors are demonstrated with the broadband response (400–1600 nm) and high responsivities of 2175 A W−1 at 980 nm outperforming those of conventional planar InGaAs photodetectors. The results show that the new growth strategy is highly feasible to achieve high‐quality InGaAs/InP MQW nanowires for the development of future optoelectronic devices and integrated photonic systems. [ABSTRACT FROM AUTHOR]

Unidirectional micro-nano-light sources have been widely applied in integrated photonics and optoelectronic devices. In this study, on-chip all-inorganic cesium lead halide perovskite nanowires are employed and excited as a bright light source to generate unidirectional light. Here, we directly image the angular emission patterns of perovskite nanowires by using fluorescence Fourier microscopy. The extinction ratio for the unidirectional emission is achieved up to 11 dB, and the detected minimum polar divergence angle reaches 8.6° in experiments. The emission direction also can be tuned flexibly within the range of 48° by changing the upper surrounding medium. Detailed calculations based on multi-mode expansion theory are used to reveal the inner physical mechanisms. Further analysis of the far-field emission patterns corresponds well with the experiment results. Our works investigating the perovskite nanowire light source emission from the perspective of Fourier space have potential applications in photon-detection and integrated photonics chips. [ABSTRACT FROM AUTHOR]

An analysis of the optoelectronic properties and photocurrent generation mechanisms in 2D multilayer crystallites of black phosphorus (BP) is conducted from 350 K down to cryogenic temperatures T of ≈6 K using a broad‐band white light source, and the results are compared to another semiconducting van der Waals solid, MoS2. Both the BP and MoS2 devices are contacted with Mo at the bottom as the electrode metal. The Mo–BP interface yields a low Schottky barrier φSB ≈ −28.3 meV and a high photoresponsivity R of ≈2.43 × 105 A W−1 at a source‐drain bias voltage of ≈0.5 V (300 K, and incident optical power ≈3.16 μW cm−2). This article is the first to highlight the empirical use of Mo as a contact metal with BP. The high R is attributed to the low φSB at the interfaces, in conjunction with the large effective area of a bottom contact architecture that increases the collection of photoexcited carriers and reduces thermal dissipation into the substrate from the largely suspended 2D nanodiaphragm. The results show the promise of BP to potentially advance thermoelectric and optoelectronic devices stemming from this monoelemental, direct bandgap 2D van der Waals solid. [ABSTRACT FROM AUTHOR]

In this work, we report on the fabrication and characterization of a miniature GaN chip with a size of $1.1\times 1.1\times0.21$ mm3 for surface roughness measurement. Unlike conventional optical metrology that requires external components for the optical coupling between light source and detector, a monolithic GaN-on-sapphire chip fabricated through wafer-scale processes provides light emission and photodetection functions and is capable of sensing a range of average surface roughness from 0.025 to $1.6~\mu \text{m}$. The sensing performances are compared with fiber-optic metrology, and the ability to real-time monitor the roughness of the moving surface is demonstrated. The novel chip offers the advantage of non-contact and non-destructive, compact structure, simple operation, and in situ measurement capability, which is highly valuable for various practical and industrial surface metrology applications. [ABSTRACT FROM AUTHOR]

Metal halide perovskites have attracted increasing attention due to their superior optical and electrical characteristics, flexible tunability, and easy fabrication processes. Apart from their unprecedented successes in photovoltaic devices, lasing action is the latest exploitation of the optoelectronic performance of perovskites. Among the substantial body of research on the configuration design and light emission quality of perovskite lasers, the random laser is a very interesting stimulated emission phenomenon with unique optical characteristics. In this review article, we first comprehensively overview the development of perovskite-based optoelectronic devices and then focus our discussion on random lasing performance. After an introduction to the historical development of versatile random lasers and perovskite random lasers, we summarize several synthesis methods and discuss their material configurations and stability in synthesized perovskite materials. Following this, a theoretical approach is provided to explain the random lasing mechanism in metal halide perovskites. Finally, we propose future applications of perovskite random lasers, presenting conclusions as well as future challenges, such as quality stability and toxicity reduction, of perovskite materials with regard to practical applications in this promising field. [ABSTRACT FROM AUTHOR]

2D materials, such as graphene, black phosphorous and transition metal dichalcogenides, have gained persistent attention in the past few years thanks to their unique properties for optoelectronics. More importantly, introducing 2D materials into silicon photonic devices will greatly promote the performance of optoelectronic devices, including improvement of response speed, reduction of energy consumption, and simplification of fabrication process. Moreover, 2D materials meet the requirements of complementary metal‐oxide‐semiconductor compatible silicon photonic manufacturing. A comprehensive overview and evaluation of state‐of‐the‐art 2D photonic integrated devices for telecommunication applications is provided, including light sources, optical modulators, and photodetectors. Optimized by unique structures such as photonic crystal waveguide, slot waveguide, and microring resonator, these 2D material‐based photonic devices can be further improved in light‐matter interactions, providing a powerful design for silicon photonic integrated circuits. [ABSTRACT FROM AUTHOR]

With the development of novel optoelectronic materials and nanofabrication technologies, integrated photonics is a rapidly developing field that will promote the development and application of next‐generation photonic devices. In recent years, emerging two‐dimensional materials (2DMs) including graphene, transition metal dichalcogenides (TMDCs), black phosphorus (BP), and ternary compounds show many complementarities and unique characteristics over those of traditional optoelectronic materials including broadband absorption, ultrafast carrier mobility, strong nonlinear effects, and compatibility for monolithic integration. Herein, the recent progress on waveguide‐integrated active devices for a full photonic circuit based on 2DMs is reviewed. Both the development of nanofabrication techniques and the working mechanism of active photonic components based on 2DMs containing integrated light sources, waveguide‐integrated modulators, photodetectors, as well as some advanced 2DMs‐based optoelectronic devices are illustrated in detail. In the end, the existing challenges and perspectives on novel 2DMs‐integrated photonics are summarized and discussed.

With the development of novel optoelectronic materials and nanofabrication technologies, integrated photonics is a rapidly developing field that will promote the development and application of next‐generation photonic devices. In recent years, emerging two‐dimensional materials (2DMs) including graphene, transition metal dichalcogenides (TMDCs), black phosphorus (BP), and ternary compounds show many complementarities and unique characteristics over those of traditional optoelectronic materials including broadband absorption, ultrafast carrier mobility, strong nonlinear effects, and compatibility for monolithic integration. Herein, the recent progress on waveguide‐integrated active devices for a full photonic circuit based on 2DMs is reviewed. Both the development of nanofabrication techniques and the working mechanism of active photonic components based on 2DMs containing integrated light sources, waveguide‐integrated modulators, photodetectors, as well as some advanced 2DMs‐based optoelectronic devices are illustrated in detail. In the end, the existing challenges and perspectives on novel 2DMs‐integrated photonics are summarized and discussed. [ABSTRACT FROM AUTHOR]

Patterned light from a laser can induce rapid self-folding of pre-strained polymer sheets. Black ink coated on the sheet absorbs the light, which converts the photon energy into thermal energy that heats the sheet locally; the temperature of the sheet is highest at the surface where the light impinges on the sheet and decreases through the sheet thickness. The gradient of temperature induces a gradient of strain relaxation through the depth of the sheet, which causes folding within seconds of irradiation. The pattern of laser light that irradiates the compositionally homogeneous two-dimensional (2D) substrate dictates the resulting three-dimensional (3D) shape. Unlike most approaches to self-folding, the methodology described here requires no patterning of pre-defined hinges. It opens up the possibility of using a patterning technique that is inherently 2D to form 3D shapes. The use of lasers also enables systematic control of key process parameters such as power, intensity, and the pattern of light (i.e., beam width and shape). The rate of folding and folding angle measured with respect to these parameters provide an indirect quantification of heat loss in the sample and thereby identify the threshold power and power intensity that must be delivered to the hinge for folding to occur. [ABSTRACT FROM AUTHOR]

Surface and interface engineering have shown broad application prospect in energy conversion. Mo2C-C/Sb2S3 composites have been synthesized by coupling Mo2C-C composites and Sb2S3 nanowires with coupling agent. The performance of the devices has been investigated. Under irradiation by light source, the device showed better electrical contact, fast response speed (rise time 0.135 s, decay time 0.132 s) and larger on/off ratio (1. 5 × 1 0 2 ) than the device which assembled by mechanical mixing (1 × 1 0 2 ) and pure Sb2S3 nanowires (47), respectively. The performance has been enhanced by modifying the surface and interface of materials. This approach provides a new idea to enhance the high-performance photodetectors and other inventive optoelectronic devices. Mo2C-C/Sb2S3 composites have been synthesized by adjusting the surface and interface. Due to different resistance and junction capacitance, these devices showed different performance index. Responsivity and response time cannot be improved simultaneously, but can only obtain one of them. This work effectively throws light on the relationship of responsivity and response time. [ABSTRACT FROM AUTHOR]

Strain engineering of germanium has recently attracted tremendous research interest. The primary goal of this approach is to exploit mechanical strain to tune the electrical and optical properties of Ge to ultimately achieve an on-chip light source compatible with silicon technology. Additionally, this can result in enhanced electrical performance for high-speed optoelectronic applications. In this paper, we demonstrate the formation of highly tensile-strained Ge islands grown on a pre-patterned (110) GaAs substrate using a depth controlled nanoindentation process. Results show that a biaxial tensile strain, up to ∼2%, can be transferred from the mechanically stamped substrate to Ge islands by optimizing the parameters of the nanoindentation process. We verified our measurements by observing the islands' photoluminescence (PL) emission properties. A strong emission at room-temperature was observed around the wavelength of 1.9 µm (650 meV). This strain-induced redshift of the PL spectra is consistent with theoretical predictions, revealing a direct Ge bandgap formation. Furthermore, we demonstrate a significant 6.5x enhancement in the PL emission signal of the direct-transition when the Ge islands are decorated by 5 nm gold nanoparticles. This is attributed to a longer optical path length interaction and a plasmonic induced high-field enhancement which increases the light absorption in the Ge islands. Furthermore, results show that GNPs can significantly modulate the energy band structure and the carrier's transportation at the nanoscale metal-germanium Schottky interface. This maskless physical approach can offer a pathway towards a practical CMOS-compatible integrated laser. Additionally, it opens possibilities for designing innovative optoelectronic devices. [ABSTRACT FROM AUTHOR]

The relationship between facet stress and reliability of AlGaInAs edge-emitting lasers is unclear despite it being an important issue. We prepared two 1.3 μm AlGaInAs Fabry–Pérot buried-heterostructure (BH) lasers that were identical except that they had tensile and compressive stress at the facet. The magnitude of the facet stress was controlled to be approximately 200 MPa in both lasers. We performed three reliability tests. In forward-biased electrostatic discharge tests, which can evaluate the resistance to optical damage, the cumulative degradation ratio of the compressive stressed laser was 33% lower than that of the tensile stressed laser. This result indicates a reduction in the optical absorption due to enlargement of the energy band gap at the facet. In the long-term aging of the light output power of 8 mW at 85 °C over 5 000 h, no dependence of the facet stress on the lifetime was observed. Since a major limitation of InP-based BH lasers is the BH interface, the aging results are reasonable. In the accelerated aging of a large current of 200 mA at 85 °C over 800 h, degradation (defined as an increase in the threshold current of over 10%) was observed only in the tensile stressed laser. This degradation differed completely from that caused by optical absorption; dislocation loops covered the entire active layer at the facet. To the best of our knowledge, this is the first time such degradation has been reported. We found the degradation depends on the facet stress and that compressive stress can suppress the degradation. [ABSTRACT FROM AUTHOR]

A multiple graphene layer (MGL) structure with a stack of GLs and a highly conducting bottom GL on SiC substrate pumped by optical radiation is considered as an active region of terahertz and far infrared lasers with external metal mirrors. The dynamic conductivity of the MGL structure is calculated as a function of the signal frequency, the number of GLs, and the optical pumping intensity. The utilization of optically pumped MGL structures might provide the achievement of lasing with the frequencies of about 1 THz at room temperature due to a high efficiency of pumping. [ABSTRACT FROM AUTHOR]

We compared the thermal performance of mid-IR GaInAs/AlInAs quantum cascade lasers (QCLs) having identical gain medium, but different heat sinking configurations. By using a two-dimensional anisotropic thermal model, we have calculated the temperature profiles and the heat flow patterns of ridge waveguide QCLs, either buried or planarized, and mounted substrate-side or epilayer-side down. Device planarization with Y2O3:Si3N4 dielectric layers gives an ∼7% reduction of the device thermal resistance with respect to InP buried heterostructures. If this planarization is combined with thick gold electroplating and epilayer-side mounting of the device, the thermal resistance is reduced by ∼34% and ∼50%, respectively, with respect to conventional ridge waveguide structures. [ABSTRACT FROM AUTHOR]

We employ a cavity-length study to determine the temperature variation of the internal loss and gain per unit current density in a ten-stage interband cascade laser that operated cw up to 269 K with an emission wavelength of 4.05 μm. The characteristic temperature for the gain per unit current density is 39 K, which is slightly lower than T0 of the threshold current and is consistent with dominance by Auger recombination. The internal loss for the 150-μm-wide mesa devices increased from 11 cm-1 at 78 K to 28 cm-1 at 275 K. [ABSTRACT FROM AUTHOR]

Purpose: Dentin hypersensivity (DH) is one of the most common complications occurring after periodontal treatment. Various methods such as Nd:YAG and Er:YAG have been used to treat DH. Previous studies support the effectiveness of these lasers, but their effect on the tooth surface largely depends on certain parameters of the tooth surface. This study attempts to evaluate some changes of the dentin surface after Nd:YAG and Er:YAG laser irradiation by using SEM. Materials and Methods: Fifteen freshly extracted mandibular molars were selected, and 4 specimens with known dimensions (1 × 2 × 2 mm) from the buccal surface and below CEJ of all the teeth were prepared to obtain a total of 60 specimens. These specimens were then divided into 4 groups. Group 1 (control) was not subjected to laser irradiation. Group 2 was subjected to Nd:YAG laser irradiation (0.5 W, 50 mJ, 10 Hz, 60 s). Group 3 was irradiated by Nd:YAG laser (1 W, 100 mJ, 10 Hz, 60 s). Group 4 was irradiated by Er:YAG laser (0.3 W, 100 mJ, 3 Hz, 60 s). After preparation and gold coating of specimens, they were observed under SEM. Finally, the number and diameter of dentinal tubules, craters, and microcracks were determined in different groups. Finally, the data were analyzed using ANOVA. Results: The number of open tubules showed significant differences between the Nd:YAG (1 W) group and other groups (p < 0.05), but no significant differences were observed between the Nd:YAG (0.5 W), Er:YAG (0.3 W), and control groups. Tubule diameter showed significant differences across all groups (p < 0.001), except between the Nd:YAG (1 W) and Er:YAG groups. Craters and carbonization were only observed in some samples of the Er:YAG group. No microcracks were detected in the study groups. Conclusion: The results of this study show that Nd:YAG and Er:YAG laser irradiation can cause thermal effects such as decreased dentinal tubule diameter or occlusion. According to this study, the Nd:YAG laser at 1 W power is more effective than the Nd:YAG at 0.5 W or Er:YAG in occluding tubules. [ABSTRACT FROM AUTHOR]

Over the past decade, the use of middle infrared (Er:YAG and Er,Cr:YSGG) lasers for caries removal and cavity preparation has become commonplace in clinical practice. These lasers are also being used increasingly for soft tissue surgery and for hard-tissue crown lengthening surgery. This paper addresses possible mechanisms that may contribute to a positive patient experience with reduced need for injected local anaesthesia during restorative dentistry when performed with lasers, and then focuses on the concept of laser-induced analgesia as a low-level effect which contributes to the reduced discomfort experienced by dental patients when pulsed middle infrared lasers (Nd:YAG as well as Er:YAG and Er,Cr:YSGG) are employed. [ABSTRACT FROM AUTHOR]

The optical properties of modulation-doped InGaN/GaN laser diodes are theoretically studied with the effects of electron spillover from quantum wells considered. We use a six-band model including the strain effect for calculating valence band states. The continuous subbands are treated by a dense discretization for the electrons spilling from the quantum wells. The calculation results show that the threshold current can be significantly reduced by p-type modulation doping around the wells but not by n-type doping, supposed that the layers are of a perfect quality and the impurity-induced defects are ignored. Also, the p-type modulation doping can make the threshold current more insensitive to the cavity loss compared with other cases. An optimized threshold current density can be achieved for single-quantum-well lasers by introducing p-type dopants. However, the dopant concentration is high and may be inaccessible. For double-quantum-well lasers an optimized low threshold current can be achieved with a slighter and practicable p-type doping level. [ABSTRACT FROM AUTHOR]

The band structure and light emission spectra from p-doped quaternary (AlXIn1-X-YGaY)N/(AlxIn1-x-yGay)N superlattices (SLs) in the zinc blend (cubic) structure are investigated by means of self-consistent calculations which are performed within the k·p approach. Exchange and correlation effects, within the generated hole gas, are taken into account in the local density approximation. The calculated luminescence and absorption spectra show that light emission, due to recombination from confined states in the wells, is redshifted in the doped systems as compared to undoped SLs. It is demonstrated that p-doped strained (AlXIn1-X-YGaY)N/(AlxIn1-x-yGay)N SLs give rise to the feasibility of achieving white light emission, through emissions covering all the visible region spectra, from violet to red. These findings provide important guidelines for the interpretation of forthcoming experiments in quaternary group-III nitride-based alloy systems, and for the design of advanced optoelectronic devices based on these alloys. [ABSTRACT FROM AUTHOR]