Modeling and admittance recursive simulation of anti-reflective coatings for photothermal conversion: synergy between subwavelength structures and gradient refractive index layers.

In the field of photothermal conversion, light-absorbing layers show limitations such as low solar energy utilization and excessive surface reflection. This paper proposes a new anti-reflective coating consisting of a gradient-doped fluorescent glass film covering a subwavelength structural layer for photothermal conversion. Its transmittance was simulated using equivalent medium theory and the admittance recursion method. The subwavelength structure provides a refractive index gradient, and its shape solves the problem of the sharp decrease in transmittance at high angles of incidence. Subsequently, we adjust the material parameters of the gradient refractive layers and control the thickness of each layer to minimize interlayer Fresnel reflections. Finally, the efficient light-trapping ability of the model was verified by calculating and comparing the transmittances of the optimized model and bare glass. Notably, within the visible spectrum, our model achieves an average transmittance of over 95% across wavelength and angle ranges, effectively suppressing surface reflections. At a larger light incident angle, the transmittance increases by 29.7%, and the minimum angle transmittance reaches 92.7%. This study proposes an innovative method to enhance the performance of transmission layers in photothermal conversion devices.

Modeling of the synergistic anti-reflection effect in gradient refractive index films integrated with subwavelength structures for photothermal conversion.

Photothermal materials generally suffer from challenges such as low photothermal conversion efficiency and inefficient full-spectrum utilization of solar energy. This paper proposes gradient refractive index transparent ceramics (GRITCs) integrated with subwavelength nanostructure arrays and simulates the synergistic anti-reflection effect by an admittance recursive model. An innovative subwavelength structure, possessing a superior light-trapping capability, is initially crafted based on this model. Subsequently, various intelligent optimization algorithms including genetic algorithm, particle swarm optimization, and simulated annealing are employed to optimize the structure of gradient refractive index films respectively. Finally, the photothermal conversion efficiencies of devices based on different photothermal materials are calculated. The simulations and finite-difference time-domain calculations demonstrate that the three-layer GRITCs integrated with an optimal SNA exhibit outstanding full-spectrum and omnidirectional anti-reflection performance. The solar transmittance of the devices can exceed 97% for light wavelengths ranging from 300 to 2500 nm over the full angle of incidence. Our results reveal that the synergistic anti-reflection effect in the SNAs and GRITCs can enhance the photothermal conversion efficiency by more than 20%.

Enhancing Linearity of Light Response in Avalanche Photodiodes by Suppressing Electrode Size Effect.

The nonlinear characteristics of avalanche photodiodes (APDs) inhibit their performance in high-speed communication systems, thereby limiting their widespread application as optical detectors. Existing theoretical models have not fully elucidated complex phenomena encountered in actual device structures. In this study, actual APD structures exhibiting lower linearity than their ideal counterparts were revealed. Simulation analysis and physical inference based on GaN APDs reveal that electrode size is a noteworthy factor influencing response linearity. This discovery expands the nonlinear theory of APDs, suggesting that APD linearity can be enhanced by suppressing the electrode size effect. A physical model was developed to explain this phenomenon, which is attributed to charge accumulation at the edge of the contact layer. Therefore, we proposed an improved APD design that incorporates an additional gap layer and a buffer layer to stabilize the internal gain under high-current-density conditions, thereby enhancing linearity. Our improved APD design increases the linear threshold for optical input power by 4.46 times. This study not only refines the theoretical model for APD linearity but also opens new pathways for improving the linearity of high-speed optoelectronic detectors.

Metamaterial Broadband Absorber Induced by Synergistic Regulation of Temperature and Electric Field and Its Optical Switching Application.

Nowadays, metamaterial absorbers still suffer from limited bandwidth, poor bandwidth scalability, and insufficient modulation depth. In order to solve this series of problems, we propose a metamaterial absorber based on graphene, VO2, gallium silver sulfide, and gold-silver alloy composites with dual-control modulation of temperature and electric field. Then we further investigate the optical switching performance of this absorber in this work. Our proposed metamaterial absorber has the advantages of broad absorption bandwidth, sufficient modulation depth, and good bandwidth scalability all together. Unlike the single inspired layer of previous designs, we innovatively adopted a multi-layer excitation structure, which can realize the purpose of absorption and bandwidth width regulation by a variety of means. Combined with the finite element analysis method, our proposed metamaterial absorber has excellent bandwidth scalability, which can be tuned from 2.7 THz bandwidth to 12.1 THz bandwidth by external electrothermal excitation. Meanwhile, the metamaterial absorber can also dynamically modulate the absorption from 3.8% to 99.8% at a wide incidence angle over the entire range of polarization angles, suggesting important potential applications in the field of optical switching in the terahertz range.

Highly Tunable Light Absorber Based on Topological Interface Mode Excitation of Optical Tamm State.

Optical absorbers based on Tamm plasmon states are known for their simple structure and high operational efficiency. However, these absorbers often have limited absorption channels, and it is challenging to continuously adjust their light absorption rates. Here, we propose a Tamm plasmon state optical absorber composed of a layered stack structure consisting of one-dimensional topological photonic crystals and graphene nano-composite materials. Using the four-by-four transfer matrix method, we investigate the structural relationship of the absorber. Our results reveal that topological interface states (TISs) effectively excite the optical Tamm state (OTS), leading to multiple absorption peaks. This expands the number of absorption channels, with the coupling number of the TIS determining the transmission quality of these channels-a value further adjustable by the period number of the photonic crystals. Tuning the filling factor, refractive index, and thickness of the graphene nano-composite material allows for a wide range of control over the device's absorption rate, from 0 to 1. Additionally, adjusting the defect layer thickness, incident angle, and Fermi energy enables us to control the absorber's operational bandwidth and the switching of its absorption effect. This work presents a new approach to expanding the tunability of optoelectronic devices.

Flexible multicolor biaxial sensor for strain direction identification based on sandwich-structured mechanoluminescent materials.

Strain sensors capable of recognizing the direction of strain are crucial in applications such as robot attitude adjustment and detection of strain states in complex structures. In this study, a sandwich-structured flexible biaxial strain sensor was developed using polydimethylsiloxane as the substrate, mechanoluminescent materials as the luminescent elements, and rubber-ink as the light-blocking layer. By correlating the emitted light color with the stretching state, precise identification of the applied strain direction is achieved. Additionally, the mechanoluminescence of the sensor is collected by a photodiode, generating photocurrent that can be analyzed. This provides a solution for practical applications of sensor.

Modeling Monte Carlo simulation on photon regeneration effects of perovskite FAPbI3 for photovoltaic applications.

Controlling the photon regeneration effects in FAPbI3 films is a noteworthy approach to improve the photovoltaic (PV) efficiency of FAPbI3-based solar cells. However, the lack of systematic study on the relationship between photon regeneration effects and PV efficiency in the experimental process makes it difficult to control the photon regeneration effects effectively. In this work, we combine the Monte Carlo sampling method and the polar coordinate calculation method to design a new algorithm for a detailed simulation of the main processes of photon regeneration effects affecting the PV efficiency in a model based on an n-i-p type FAPbI3 perovskite solar cell (PSC). The algorithm is validated to be used to compare the power-conversion efficiency (PCE) of different PSCs to filter out the PSC structure with the highest PCE or to determine the range of material parameter values corresponding to the highest PCE. This work opens up new ideas to effectively control the photon regeneration effects in PSCs to improve the device PV efficiency.

Structures, photoluminescence, and principles of self-activated phosphors.

Self-activated phosphors without any luminescent dopants, usually display excellent optical properties, such as high oscillator strength, large Stokes shift, and strong luminescence efficiency, and thus have been widely investigated by researchers for several decades. However, their recent advancements in scintillators, white-light illumination, displays and optical sensors compel us to urgently understand the basic principles and significant technological relevance of this worthy family of materials. Herein, we review the structures, photoluminescence principles, and applications of state-of-the-art self-activated phosphors, such as borate, gallate, niobate, phosphate, titanate, vanadate, tungstate, nitrides, oxyfluoride, perovskite, metal halides, and carbon dots. The photoluminescence principles of self-activated phosphors are mainly summarized as transitions between energy levels of rare-earth and transition metal ions, charge transfer transitions of some oxide compounds, and luminescence in all-inorganic semiconductors. The different self-activated phosphors exhibit various structures and site-dependent spectra. Additionally, we discuss the application prospect and main challenges of self-activated phosphors.

Structures, principles, and properties of metamaterial perfect absorbers.

Metamaterials are a kind of artificial material with special properties, showing huge potential for applications in fields such as infrared measurement, solar cells, optical sensors, and optical stealth. A metamaterial perfect absorber (MPA) is designed based on a metamaterial, featuring strong absorption, small volume, light weight, ultra-bandwidth, tunability and other characteristics. This paper introduces the absorption mechanism of MPAs from microwave to optical wave band, and four directions of absorber design are elaborated. Equivalent impedance matching, plasma resonance and interference effect are the main absorption mechanisms of MPA. Multiband perfect absorption, ultra-wideband and ultra-narrowband perfect absorption, polarization and angle insensitive absorption, and dynamically controllable tunable absorption are the main design aspects. Among them, the proposal of a dynamically tunable absorber realizes the dynamic absorption. Finally, the problems and challenges of metamaterial perfect absorber design are discussed.

Effectiveness of cognitive behavioral therapy for patients after total knee arthroplasty: a systematic review and meta-analysis.

Total knee arthroplasty (TKA) is considered a common surgical option in patients with end-stage osteoarthritis of the knee. This systematic review and meta-analysis aimed to determine the effectiveness of cognitive behavioral therapy (CBT) for patients after TKA. PubMed, EMBASE, the Cochrane Library, Web of Science and CINAHL were searched for randomized controlled trials (RCTs) from inception to 20 August 2021. Included studies were evaluated with the Cochrane risk-of-bias tool. Six RCTs were included. Our study results demonstrated that a significant reduction in pain catastrophing was seen in patients receiving CBT at post-intervention (SMD -0.48, 95% CI = -0.72 to -0.23, I2 17.2%, p = 0.00) but not in 3-month or 12-month follow-up. There were no significant differences between CBT and usual-care patients regarding pain intensity or knee function at different time-points. This is the first time that meta-analysis has been conducted to determine the effectiveness of CBT for patients after TKA. It is necessary to conduct longer follow-ups, include larger samples and conduct rigorous RCTs to further explore this issue.

Pain catastrophizing and associated factors in preoperative total knee arthroplasty in Lanzhou, China: a cross-sectional study.

BACKGROUND: Pain catastrophizing in preoperative total knee arthroplasty (TKA) patients is associated with several poorly characterised factors in the literature. This study investigated the current state and associated factors of preoperative pain catastrophizing in patients undergoing TKA. METHODS: This descriptive cross-sectional study was conducted at the orthopedics ward of two tertiary hospitals in Lanzhou, China. Pain catastrophizing was measured using the Chinese versions of the Pain Catastrophizing Scale, Short Form-36 (physical function domain), Numerical Rating Scale, Oxford Knee Score, Hospital Anxiety and Depression Scale, and Life Orientation Test-Revised. RESULTS: The study included 360 participants. Preoperative TKA pain catastrophizing in all patients was high, with a mean score of 24.92 (SD: 12.38). The stepwise multiple linear regression analysis revealed anxiety (ß = 0.548, P < 0.01), education level (ß = - 0.179, P < 0.01), physical function (ß = - 0.156, P < 0.01), and pain intensity during activity (ß = 0.105, P = 0.015) as associated factors for pain catastrophizing, possibly explaining 51.2% of the total variation (F = 95.149, P < 0.01). CONCLUSION: Anxiety was the most relevant factor for pain catastrophizing in patients with preoperative TKA. Lower education levels, poor physical function, and stronger pain intensity during the activity were also associated with pain catastrophizing.

Structures, plasmon-enhanced luminescence, and applications of heterostructure phosphors.

Heterostructure phosphor composites have been used widely in the fields of targeted bio-probes and bio-imaging, hyperthermia treatment, photocatalysis, solar cells, and fingerprint identification. The structures, plasmon-enhanced luminescence and mechanism of metal/fluorophore heterostructure composites, such as core-shell nanocrystals, multilayers, adhesion, islands, arrays, and composite optical glass, are reviewed in detail. Their extended applications were explored widely since the surface plasmon resonance effect increased the up-conversion efficiency of fluorophores significantly. We summarize their synthesis methods, size and shape control, absorption and excitation spectra, plasmon-enhanced up-conversion luminescence, and specific applications. The most important results acquired in each case are summarized, and the main challenges that need to be overcome are discussed.

Effect of light scattering on upconversion photoluminescence quantum yield in microscale-to-nanoscale materials.

Scattering affects excitation power density, penetration depth and upconversion emission self-absorption, resulting in particle size -dependent modifications of the external photoluminescence quantum yield (ePLQY) and net emission. Micron-size NaYF4:Yb3+, Er3+ encapsulated phosphors (∼4.2 µm) showed ePLQY enhancements of >402%, with particle-media refractive index disparity (Δn): 0.4969, and net emission increases of >70%. In sub-micron phosphor encapsulants (∼406 nm), self-absorption limited ePLQY and emission as particle concentration increases, while appearing negligible in nanoparticle dispersions (∼31.8 nm). These dependencies are important for standardising PLQY measurements and optimising UC devices, since the encapsulant can drastically enhance UC emission.

Monte Carlo simulation and experimental evaluation of the quantum efficiency of Eu3+-doped glass at different temperatures.

The quantum efficiency (QE) is a key parameter to evaluate the optical properties of fluorescent glass. However, it is very difficult to measure the QE at high temperatures by the integrating sphere test system. In this paper, we report a new method to calculate the QE of five kinds of Eu3+-doped glasses at different temperatures based on experimental absorption and excitation spectra of Eu3+-doped glasses. The simulated QE values agree well with the experimental values of QE. Furthermore, the influence of the shape, refractive index and temperature on the QE and the spatial light intensity distribution of the Eu3+-doped glass is studied based on the Monte Carlo method. This work presents a simple method to calculate the QE and the spatial light intensity distribution at different temperatures.

Morphology control, spectrum modification and extended optical applications of rare earth ion doped phosphors.

Rare earth ion (RE3+) doped nano-phosphors with controllable morphologies have a wide range of applications in laser crystals, LEDs, bio-probes, photo-catalysis, three-dimensional displays, sensors, and flash memories. This review summarizes the morphology control strategy, phase transfer theory, spectrum modulation, and extended optical applications of RE3+-doped phosphors. The roles of surfactants in the morphology control in the liquid-solid-solution phase transfer process for RE3+-doped fluorides, oxides and other compounds are discussed. The relevant mechanisms of controlling morphologies are illustrated. The size- and shape-dependent optical properties of RE3+ doped phosphors, including the emission intensities, intensity ratios of adjacent emission bands, decay times and thermal stability, are analyzed. The extended optical applications and main challenges of RE3+-doped phosphors are also discussed.

Photolithographic nanoseeding method for selective synthesis of metal-catalysed nanostructures.

In this work we present a general method for the selective synthesis by photolithography of localised nanostructures in planar geometries. The methodology relies on the previous concept of photo-patternable metallic nanoparticle (NP)/polymer nanocomposites, which can provide a range of NP sizes, polydispersity and densities. First, a photoresist containing metallic ions is patterned by photolithography. Silver NPs are synthesised in situ after the exposure and development of the patterned thin film via the thermal-induced reduction of ions embedded in its structure. Gentle plasma ashing is used to selectively remove the polymer, which leaves NPs on the patterned areas. These NPs are used as seeds for subsequent processes. In order to demonstrate the flexibility of the method, its use to selectively produce localised nanostructures through different processes is shown here. Following a top-down approach, high aspect-ratio silicon nanograss has been produced by reactive ion etching and masking by the NPs. In a bottom-up approach, 280 nm copper clusters have been selectively grown in arrays. This method can be easily extrapolated to other metals and it provides a quick way to selectively generate hierarchical nanostructures in large planar areas that can be used for different applications, such as the fabrication of nanostructured sensor arrays.

Detecting Variable Resistance by Fluorescence Intensity Ratio Technology.

We report a new method for detecting variable resistance during short time intervals by using an optical method. A novel variable-resistance sensor composed of up-conversion nanoparticles (NaYF4:Yb3+,Er3+) and reduced graphene oxide (RGO) is designed based on characteristics of a negative temperature coefficient (NTC) resistive element. The fluorescence intensity ratio (FIR) technology based on green and red emissions is used to detect variable resistance. Combining the Boltzmann distributing law with Steinhart-Hart equation, the FIR and relative sensitivity SR as a function of resistance can be defined. The maximum value of SR is 1.039 × 10-3/Ω. This work reports a new method for measuring variable resistance based on the experimental data from fluorescence spectrum.

Enhanced insulating behavior in the Ir-vacant Sr2Ir1-xO4 system dominated by the local structure distortion.

Sr2IrO4, known as the Jeff = 1/2 Mott insulator, was predicted to be an unconventional superconductor upon doping since it highly resembles the high-temperature cuprates. However, recent work pointed out an enhanced insulating behavior in the Ir-vacant Sr2Ir1-xO4 system. In this contribution, to investigate the microscopic mechanism of its enhanced insulating behavior, X-ray absorption spectroscopy was applied to study the electronic structure and local structure distortion of Sr2Ir1-xO4. Due to the presence of Ir5+ ions, the preconceived holes are barely doped in the Ir-vacant system. Nevertheless, Ir vacancies finely modulate the local atomic structure, i.e. the topology of IrO6 octahedra and the in-plane Ir-O1-Ir bond angle. Combined with theoretical calculations, it is demonstrated that both the more distorted IrO6 octahedra and decreased Ir-O1-Ir angle contribute to the increment of the band gap, and then result in the enhanced insulating state for Sr2Ir1-xO4.

Modifying phase, shape and optical thermometry of NaGdF4:2%Er3+ phosphors through Ca2+ doping.

An efficient soft chemistry method to modify the phase, shape and optical thermometry of NaGdF4:2%Er3+ nano-phosphors through doping Ca2+ ion is reported. With the introduction of Ca2+, the phase changes from the GdF3:2%Er3+ to NaGdF4:2%Er3+ was achieved, and the shapes of NaGdF4:2%Er3+ were modified from irregular particles to pure hexagonal NaGdF4 microtubes. These modifications derive from the charge redistribution on the nucleus surface through internal electron charge transport between Gd3+ in a lattice and co-doped Ca2+ ion. An obvious enhancement of the total fluorescence intensity was observed after doping the Ca2+ ion. Moreover, an interesting phenomenon was observed that the fluorescence intensity of the mixed GdF3:2%Er3+ and NaGdF4:2%Er3+ was not be quenched at the high temperature more than 473 K. A maximum relative sensitivity of 0.00213/K (416 K) was obtained at 20%Ca2+ doping. These results indicate that NaGdF4:Er3+/Ca2+ can be applied in optical temperature sensor.

Excitation power dependent optical temperature behaviors in Mn4+ doped oxyfluoride Na2WO2F4.

A Mn4+ doped Na2WO2F4 phosphor was synthesized through a two-step wet chemical method. The relationship between crystal structure and luminescence properties is discussed and unusual strong intense zero phonon lines (ZPLs) have been found in a distorted octahedral environment. The power dependent luminescence spectra exhibit the existence of down conversion luminescence intensity saturation under a high pumping power limit. The fluorescence intensity ratios of anti-Stokes bands to the ZPL and Stokes bands reveal an obvious temperature dependent relationship based on thermal de-population from the low states to the upper states of an intrinsic Mn4+ 2Eg → 4A2g transition. The temperature dependent emission intensity of Mn4+ is investigated by changing the excitation power, and an optical temperature sensitivity as high as 0.00658 K-1 is achieved at 193 K with the intensity ratio of anti-Stokes bands to the ZPL under 488 nm excitation by a Xenon lamp. This work presents a new method to realize optical thermometry at low temperature by controlling the intensity ratio of the anti-Stokes bands to the ZPL.