Atmospheric Window Research Articles

Advances in Lanthanide-Based NIR-IIb Probes for In Vivo Biomedical Imaging.

The past decades have witnessed the significant development and practical interest of in vivo biomedical imaging technologies and optical materials in the second-near infrared (NIR-II, 1000-1700 nm) window. Imaging with the extended emission wavelength toward the long-wavelength end (NIR-IIb, 1500-1700 nm) further offers micrometer imaging resolution and centimeter tissue penetration depth by taking advantage of the much-reduced photon scattering and near-zero tissue autofluorescence background, which have become a very hot research area. This review focuses on the recent advances in the development of lanthanide-based NIR-IIb probes for in vivo biomedical applications. The progress including ratiometric imaging, multiplexed imaging for wide-field and microscopy, lifetime multiplexing and sensing, persistent luminescence, and multimodal imaging is summarized. Challenges and future directions concerning the investigation of the photophysical and photochemical properties of NIR-IIb probes, the selection of near-infrared cameras as well as the potential extension of the NIR-IIb imaging sub-window are pointed out. This review will inspire readers who have a strong interest in developing optical imaging technology and long-wavelength fluorescence probes for high-contrast in vivo biomedical applications.

Powder‐Sintered Hierarchically Porous PMMA with Optimal Pore Parameters for Passive Daytime Radiative Cooling

AbstractPorous radiative cooling polymers have drawn significant attention for passive daytime cooling due to their desirable cooling performance and easy scalability. Since optimal pore parameters (i.e., pore diameter and porosity) will enhance light scattering, polymethyl methacrylate (PMMA) powders are sintered to fabricate samples with different pore parameters by the one‐step full‐dry powder sintering method. These samples have a hierarchically porous structure with pore diameters <5.0 µm. The most porous sample has 43% porosity, 0.964 reflectance in the 0.3–2.5 µm wavelength range, and 0.967 emittance in 8–13 µm wavelength range (which is the atmospheric window). The measured cooling temperature difference decreases when the porosity is low for hierarchically porous PMMA with similar pore size distribution. The high sub‐ambient cooling temperature reduction provided by hierarchically porous PMMA with optimal pore parameters is due to high solar reflectance when illuminated by the sun. Similar cooling trends are evident when sunlight is simulated by a Xenon lamp and an optical filter. The powder‐sintered hierarchically porous PMMA with optimal pore parameters can be an excellent radiative cooler for passive daytime cooling applications.

Theoretical investigation of two ideal radiative cooling materials and radiative sky water-cooling module with ideal selective radiative materials

Radiative sky cooling (RSC) is a passive approach to cool an object by emitting infrared thermal radiation to the cold outer space without any energy input and any pollutant produced. It has the potential to meet the rapidlygrowingdemandfor cooling. Radiative cooling materials and real-world applications are two concerns in RSC field. In this study, the cooling performance of two types of ideal radiative cooling materials are compared in term of the cooling power. The critical temperature at which broadband radiative materials exhibit cooling effect outside the atmospheric window is expressed as a fuction of the ambient temperature and the average atmospheric emissivity outside the atmospheric window. The temperature range for the broadband radiative materials with cooling effect outside the atmospheric window is very small, and thus selective radiative materials should be prioritized. Heat transfer processes of radiative sky water-cooling (RSWC) module with ideal selective radiative materials, which has broad application prospect, are then investigated by a theoretical model. As for ten-hour cooling process of a RSWC module under reference conditions, the temperature difference between the environment and the radiative panel rises to 5.68 °C, the temperature difference between the environment and the water rises to 3.76 °C, and the cooling power decreases from 53.5 W/m2 to 38.5 W/m2.The impact of night-time air temperature on the cooling power may reach up to 48.3 % when the atmospheric emissivity within the atmospheric window is 0.5. If the average atmospheric emissivity within the atmospheric window increases from 0.2 to 0.5 the cooling power of RSWC module decreases by 29.2 % − 39.2 %.

Daytime radiative cooling using pattern free metal dielectric coating

Radiative coolers, which dumps the excess heat to the cold outer space by releasing the thermal radiation through the atmospheric window, have offered an alternate and feasible solution to the conventional coolers that are fueled on the electricity produced by either using renewal or non-renewal sources like fossil fuels. Particularly, daytime passive radiative coolers have paved the way for many energy free technology that are used in reducing the temperature of building tops, power plants, and water harvesting. In this, we propose a pattern free and large area scalable bi-layered thin film based daytime radiative cooler. The proposed design illustrates an average reflectivity of 98.5% for the solar spectrum, while showing average emittance of 91% within the atmospheric window (8-13μm). The design consists of thin films of transparent dielectrics such as ZnS or BaF2 placed on top of a thick glass substrate, that is backed by a thin film silver. We theoretically obtained a cooling power of 119 W.m−2 with a temperature reduction of 9 °C below the ambient.

A two-dimensional thin film structure with spectral selective emission capability suitable for high-temperature environments

Spectral selective emission materials, characterized by their high emission efficiency within specific wavelength ranges, play a crucial role in various fields such as infrared stealth and radiative cooling. In this study, leveraging the tunneling effect of ultrathin metal layers and the impedance matching principle, we designed a one-dimensional multilayer thin film structure composed of Mo/Ge/Al. This design successfully achieved spectral selective emission within the 3-14 μm infrared spectrum range, showcasing superior high-temperature infrared stealth capabilities. Research findings indicate that the infrared atmospheric window (ε3-5 μm=0.40, ε8-14 μm=0.30) maintains a low emissivity within the temperature range from room temperature to 400°C, while high emissivity in non-infrared atmospheric windows (ε5-8 μm=0.81) enables radiative cooling. The use of high emissivity in the non-infrared atmospheric window reduced the surface temperature of this structure by 15.3°C compared to untreated Si substrate under similar heating conditions. The temperature reduction was 34.1°C when compared to a Si substrate coated with a 200 nm Al film. This straightforward and easily scalable structure not only presents novel solutions for applications in infrared stealth and radiative cooling but also holds vast potential for diverse fields including military, aerospace, and industrial manufacturing, injecting fresh impetus and possibilities into technological advancement.

Sustainable passive radiation cooling transparent film for mobile phone protective screens

Passive daytime radiative cooling (PDRC) is a promising approach to address energy, environmental, and safety issues caused by global warming, with high emissivity in a transparent atmospheric window and high reflectivity in the solar spectrum. However, most demonstrations of PDRC rely mainly on complex and expensive spectral selective nanophotonic structures, requiring specialized photonic structures that are both expensive and difficult to obtain. The superiorities of low-cost, abundant resources, renewability, and high value-added biomass resources prompt Gleditsia sinensis polysaccharides (GSP) to be used in thermal emission materials to explore further the characteristics of regulating object temperature within a specific range without any external energy consumption. The three-layer thermal emission film (PDMS3PG3/t4) obtained by the scalable scraping method has high transparency, hydrophobicity (114.2°), and super flexibility. The spectral variations of non-selective PDMS3PG3/t4 (1.0 wt% GSP, 800 μm thickness) in the 3–5 μm and 8–13 μm waveband ranges were discussed in detail, and high emissivities of 69.1 % and 92.2 % were obtained, respectively. PDMS3PG3/t4 was appointed a mobile phone screen film and experimented with a 4.9 °C average temperature difference below ambient temperature, materializing prime PDRC and desiring to broaden the passive cooling technology and reduce the global energy burden.

Absolute Reference for Microwave Polarization Experiments. The COSMOCal Project and its Proof of Concept

Context. The cosmic microwave background (CMB), a remnant of the Big Bang, provides unparalleled insights into the primordial universe, its energy content, and the origin of cosmic structures. The success of forthcoming terrestrial and space experiments hinges on meticulously calibrated data. Specifically, the ability to achieve an absolute calibration of the polarization angles with a precision of <0.°1 is crucial to identify the signatures of primordial gravitational waves and cosmic birefringence within the CMB polarization. Aims. We introduce the COSmological Microwave Observations Calibrator project, designed to deploy a polarized source in space for calibrating microwave frequency observations. The project aims to integrate microwave polarization observations from small and large telescopes, ground-based and in space, into a unified scale, enhancing the effectiveness of each observatory and allowing robust combination of data. Methods. To demonstrate the feasibility and confirm the observational approach of our project, we developed a prototype instrument that operates in the atmospheric window centered at 260 GHz, specifically tailored for use with the NIKA2 camera at the IRAM 30 m telescope. Results. We present the instrument components and their laboratory characterization. The results of tests performed with the fully assembled prototype using a Kinetic Inductance Detectors-based instrument, similar concept of NIKA2, are also reported. Conclusions. This study paves the way for an observing campaign using the IRAM 30 m telescope and contributes to the development of a space-based instrument.

Short-Wave Infrared Upconverting Nanoparticles.

Optical technologies enable real-time, noninvasive analysis of complex systems but are limited to discrete regions of the optical spectrum. While wavelengths in the short-wave infrared (SWIR) window (typically, 1700-3000 nm) should enable deep subsurface penetration and reduced photodamage, there are few luminescent probes that can be excited in this region. Here, we report the discovery of lanthanide-based upconverting nanoparticles (UCNPs) that efficiently convert 1740 or 1950 nm excitation to wavelengths compatible with conventional silicon detectors. Screening of Ln3+ ion combinations by differential rate equation modeling identifies Ho3+/Tm3+ or Tm3+ dopants with strong visible or NIR-I emission following SWIR excitation. Experimental upconverted photoluminescence excitation (U-PLE) spectra find that 10% Tm3+-doped NaYF4 core/shell UCNPs have the strongest 800 nm emission from SWIR wavelengths, while UCNPs with an added 2% or 10% Ho3+ show the strongest red emission when excited at 1740 or 1950 nm. Mechanistic modeling shows that addition of a low percentage of Ho3+ to Tm3+-doped UCNPs shifts their emission from 800 to 652 nm by acting as a hub of efficient SWIR energy acceptance and redistribution up to visible emission manifolds. Parallel experimental and computational analysis shows rate equation models are able to predict compositions for specific wavelengths of both excitation and emission. These SWIR-responsive probes open a new IR bioimaging window, and are responsive at wavelengths important for vision technologies.

Three-layered films enable efficient passive radiation cooling of buildings

Abstract To address the excessive energy consumption of building cooling, the coverage of passive radiation cooling materials on the surface of buildings can effectively save the global refrigeration power resources and reduce the greenhouse gas emissions generated by refrigeration equipment. In this work, passive radiation hydrophobic fabric cooling materials with three functional layers (i.e., top polydimethylsiloxane [PDMS] film layer for solar emissivity, middle polymethylmethacrylate [PMMA] film layer for solar reflectivity, and bottom cotton fabric layer for support) were prepared. This passive radiation cooling material with optimized thickness of PDMS (1.5 mm) and PMMA (3.5 mm) have a rich uneven filament structure and ideal internal bonding structure, which enabled 94% of solar reflectivity and 93.4% of atmospheric window emissivity (8–14 μm). Top layer of the composite film was hydrophobic (a contact angle of 117°) and allowed the rolling of water droplets to remove most of the surface dust. Moreover, these composites presented an excellent cooling of 7.7–15.0°C in the outdoor real cooling test. For medium-sized houses, the roof covered with composite was expected to reduce the emission CO2 by 17% every year. The findings of this work indicated that the prepared three-layered radiation cooling materials have great potentials in thermal energy storage buildings.

Pb2TeV2O10: A Lead Vanadate Tellurate with Wide Mid-IR Transparency and Large Birefringence Induced by Multiple Birefringence-Active Groups.

Birefringent materials as the key materials in laser science and technology have attracted continuous attention due to their ability to modulate polarized light. Herein, a new lead vanadate tellurate, Pb2TeV2O10, has been synthesized through the rational integration of different kinds of birefringence-active functional units. Pb2TeV2O10 features a unique two-dimensional (2D) [TeV2O10]∞ layered structure consisting of [VO6]7- and [TeO6]6- octahedra, and Pb2+ cations reside between the [TeV2O10]∞ layers. In addition, the rare edge-sharing mode of [VO6]7- and [TeO6]6- octahedra was found in this structure. Attributed to the high polarizability and appropriate arrangement of PbO8, VO6, and TeO6 units, Pb2TeV2O10 possesses a great theoretical birefringence of 0.275 at 532 nm, which is the largest among the vanadate tellurate family. The spectral tests also prove that Pb2TeV2O10 showcases a broad transparency window (439 nm-10 μm), covering an important mid-infrared (IR) atmospheric window (3-5 μm). In addition, in order to improve the transparency, alkali and alkaline earth metal cations were introduced by the substitution strategy, and then the compound K2Sr2Te2O9 was synthesized. It owns a shorter ultraviolet (UV) cutoff edge of 234 nm and a wider transparency window (234 nm-13.8 μm). The findings of Pb2TeV2O10 and K2Sr2Te2O9 enrich the structure chemistry of the tellurate family and provide new insights for designing new compounds with large optical anisotropy and wide spectral transparency.

All-day freshwater harvesting enabled by designing benzoxazine molecule with intrinsic photothermal conversion and radiation cooling ability

The importance of clean water resources for human health and economic development cannot be overlooked. Providing a way for fully passive all-day freshwater harvesting presents a significant challenge. Herein, we propose a strategy for all-day freshwater harvesting passively through a freestanding Janus film which combining solar-driven interfacial desalination during day time and dew water generation driven by passive radiative cooling at night. Specifically, the core of the strategy was a new bio-based benzoxazine which containing high-infrared emittance in the atmospheric window and the resultant cured black freestanding film owns a steady high light absorbance in the whole range of the solar irradiation wavelength. The home-made device made by the Janus film achieved a drinkable freshwater collection efficiency of 90.9 % when desalinating seawater under 1 sun illumination and achieved a dew water collection rate of 68.36 g m−2 day−1 at night. Moreover, the film has an excellent antibacterial effect, which ensures the quality of water collection and enhances the service life. Combining the advantages of bio-based raw materials, a simple fabrication process and scalability of the film, the all-day freshwater collection system makes a promising solution to alleviate freshwater shortage in many arid regions, islands and even boats sailing on the sea.

The radiative efficiency and global warming potential of HCFC-132b.

Hydro-chloro-fluoro-carbons (HCFCs) are potent greenhouse gases which strongly absorb the infrared (IR) radiation within the 8 - 12 μm atmospheric windows. Despite international policies schedule their phasing out by 2020 for developed countries and 2030 globally, HCFC-132b (CH2ClCClF2) has been recently detected with significant atmospheric concentration. In this scenario, detailed climate metrics are of paramount importance for understanding the capacity of anthropogenic pollutants to contribute to global warming. In this work, the radiative efficiency (RE) of HCFC-132b is experimentally measured for the first time and used to determine its global warming potential (GWP) over 20-, 100- and 500-year time horizon. Vibrational- and rotational-spectroscopic properties of this molecule are first characterized by exploiting a synergism between Fourier-transform IR (FTIR) spectroscopy experiments and quantum chemical calculations. Equilibrium geometry, rotational parameters and vibrational properties predicted theoretically beyond the double-harmonic approximation, are employed to assist the vibrational assignment of the experimental trace. Finally, FTIR spectra measured over a range of pressures are used to determine HCFC-132b absorption cross section spectrum from 150 to 3000 cm-1, from which istantaneous and effective REs are derived and, in turn, used for GWP evaluation.

Macro-Nanoporous Film with Cauliflower-Shaped Fibers for Highly Efficient Passive Daytime Radiative Cooling.

Passive daytime radiative cooling (PDRC) is a simple and effective cooling approach that does not consume any extra energy just by highly reflecting shortwave sunlight and highly radiating infrared heat through the atmospheric windows. In recent years, the application of photonic coolers and metamaterials for PDRC has been studied. However, they usually have complex processes and high precision requirements, which seriously limit large-scale fabrication. In this paper, a high-performance polyvinylidene difluoride-hexafluoropropylene (PVDF-HFP) PDRC fiber film was prepared by a simple and efficient electrospinning method combined with phase separation, and the obtained PVDF-HFP fibers have a cauliflower-shaped macro-nanoporous structure. The cauliflower-shaped structure provides more scattering sites of the fibers, and the fiber film with the macro-nanoporous morphology has a high scattering ability in the solar region, resulting in a high solar reflectivity of 99.65%. The PVDF-HFP porous film possesses an emissivity of 90.44% in the atmospheric window, and it can reach a maximum cooling temperature of 10.2 °C during the daytime. In addition, the excellent mechanical strength provides a guarantee for its large-scale practical application. This study offers an effective improvement strategy for the spectral performance of polymer fiber films, which is meaningful for green cooling management and reduction of carbon emission.

Experimental and theoretical study on building integrated radiative cooling with a limited sky-view factor

Building integrated radiative cooling (BIRC) technology leverages the coldness of outer space through the 8–13 μm atmospheric window for cooling. While BIRC's thermal performance has been widely studied across various climates, urban areas with obstructed sky views pose unique challenges often overlooked. To address this gap, the sky-view factor (SVF) was introduced as a metric to gauge BIRC effectiveness in urban settings. The novelty of this study lies in the experimental validation of SVF's impact on radiative cooling. A novel theoretical model was developed and validated, which was then applied to calculate BIRC's hourly, monthly, and year-round cooling power under Shenzhen's varying SVF conditions. The results revealed significant temperature drops in the RC module, ranging from 4.57 °C to 0.11 °C as SVF decreased from 0.7 to 0.1. Additionally, a numerical model was created based on experimental data, further validating the findings. This comprehensive analysis of SVF's effects on BIRC in Shenzhen's climate demonstrated that RC capacity averaged 57.27 W/m2 for SVF 0.9 but dropped below 22.55 W/m2 when SVF decreased to 0.3 or lower throughout the year. These insights enhance our understanding of BIRC's potential and limitations in densely populated urban environments.

The Solar FUV-UV Spectra Measurement Experiment in the Near Space by High Altitude Balloon

An experiment measuring the solar far-ultraviolet-ultraviolet (FUV-UV) irradiance with spectral resolution better than 0.1 nm in the wavelength range from 170 to 400 nm was carried out by the “HongHu-6” high-altitude balloon that flew to the bottom region of the near-space in September 2022. This experiment was based on the fact that solar FUV-UV penetrates through a complex cross-section window of the upper atmosphere, from outer to near space. The solar FUV-UV deposits energy in the upper atmosphere, which provides a key to answer scientific questions on the most important energy contributor to overall heating sources of the near space and how the near-space environment responds to solar activities. In the wavelength range between 150 and 210 nm, irradiance maps from active regions of the solar corona, the comparative small cross-section of molecular oxygen allows certain wavelengths of the band to arrive at altitudes between 20 and 30 km above the ground, indicating solar flares could directly impact the bottom region of the near space. Solar UV irradiance in the wavelength range 210 – 400 nm is absorbed by the upper atmosphere as a function of wavelength, and energy is deposited vertically in the lower regions of the near space. This experiment historically provides measurement data to fill a gap in the wavelength shorter than 280 nm in the lower regions of the near space. The solar FUV-UV spectrometer (SUVS) is a compact instrument based on improved Roland circle optics to adapt to the “HongHu-6” balloon payload platform. In this paper, we introduce the scientific goals of the solar FUV-UV spectrum measurement experiment, provide information on the SUVS instrument preflight calibration, and present the first results from the flight data.

Self-adaptive radiation recuperator with double phase transition temperature switches based on VO2 intelligent films

Developing renewable energy for heating and cooling to achieve carbon neutrality and environmental protection is of great significance. The combination of photothermal (PT) and radiative cooling (RC) technology to continuously obtain energy throughout the day is gradually attracting interest, in which vanadium dioxide (VO2) intelligent phase transition film serves as a bridge between the daytime PT mode and the nighttime RC mode. The high phase transition temperature of VO2 poses a challenge to environmental adaptability and dynamic switching in practical applications. In this work, a novel self-adaptive radiation recuperator with double phase transition temperature (37 °C and 68 °C) switches is proposed to exchange energy from the sun and outer space by radiation. Compared with VO2 and W-doped VO2 single-layer structure, this method has a higher self-adaptability to easily achieve the phase transition temperature of mode switching. The absorptivity of the radiation recuperator is 0.75 in the solar band (0.3–2.5 μm), and the emissivity switching capability is present from 0.3 to 0.86 in the atmospheric window band (8–14 μm). The transition mode generated by the presence of double phase transition temperature improves temperature self-adaptability and improves energy collection efficiency in dynamic environments.

Advancing CubeSats Capabilities: Ground-Based Calibration of Uvsq-Sat NG Satellite’s NIR Spectrometer and Determination of the Extraterrestrial Solar Spectrum

Uvsq-Sat NG is a French 6U CubeSat (10 × 20 × 30 cm) of the International Satellite Program in Research and Education (INSPIRE) designed primarily for observing greenhouse gases (GHG) such as CO2 and CH4, measuring the Earth’s radiation budget (ERB), and monitoring solar spectral irradiance (SSI) at the top-of-atmosphere (TOA). It epitomizes an advancement in CubeSat technology, showcasing its enhanced capabilities for comprehensive Earth observation. Scheduled for launch in 2025, the satellite carries a compact and miniaturized near-infrared (NIR) spectrometer capable of performing observations in both nadir and solar directions within the wavelength range of 1100 to 2000 nm, with a spectral resolution of 7 nm and a 0.15° field of view. This study outlines the preflight calibration process of the Uvsq-Sat NG NIR spectrometer (UNIS), with a focus on the spectral response function and the absolute calibration of the instrument. The absolute scale of the UNIS spectrometer was accurately calibrated with a quartz-halogen lamp featuring a coiled-coil tungsten filament, certified by the National Institute of Standards and Technology (NIST) as a standard of spectral irradiance. Furthermore, this study details the ground-based measurements of direct SSI through atmospheric NIR windows conducted with the UNIS spectrometer. The measurements were obtained at the Pommier site (45.54°N, 0.83°W) in Charentes–Maritimes (France) on 9 May 2024. The objective of these measurements was to verify the absolute calibration of the UNIS spectrometer conducted in the laboratory and to provide an extraterrestrial solar spectrum using the Langley-plot technique. By extrapolating the data to AirMass Zero (AM0), we obtained high-precision results that show excellent agreement with SOLAR-HRS and TSIS-1 HSRS solar spectra. At 1.6 μm, the SSI was determined to be 238.59 ± 3.39 mW.m−2.nm−1 (k = 2). These results demonstrate the accuracy and reliability of the UNIS spectrometer for both SSI observations and GHG measurements, providing a solid foundation for future orbital data collection and analysis.

Difference‐Frequency Generation of 0.2‐mJ 3‐Cycle 9‐µm Pulses from Two 1‐kHz Multicycle OPCPAs

AbstractIntense long‐wave infrared (LWIR) femtosecond pulses within the 8−14 µm atmospheric window present an array of applications, such as in strong‐field physics, ultrafast nonlinear spectroscopy, and self‐guided atmospheric propagation. However, the realization of an LWIR source capable of delivering millijoule‐class energy, few‐cycle duration, and kHz repetition rate concurrently remains challenging. Here, such an LWIR source via the combination of different nonlinear parametric processes is reported, driven by a 1 kHz Yb:YAG thin‐disk laser. The system comprises two parallel multi‐cycle optical parametric chirped‐pulse amplifiers (OPCPAs) operating at 2.3 and 3.1 µm, respectively, alongside a stage of ZnGeP2‐crystal‐based difference‐frequency generation (DFG). The resulting 9 µm DFG pulses have a record energy of 0.21 mJ, a 3‐cycle duration, a 1 kHz repetition rate, and long‐term energy stability. The simultaneous output of three synchronized intense lasers at short‐wave infrared (2.3 µm), mid‐wave infrared (3.1 µm), and LWIR (9 µm) renders the source particularly appealing for multicolor ultrafast applications.

Dual-dielectric Fabry-Perot film for visible-infrared compatible stealth and radiative heat dissipation

Multiband camouflage of space satellite to against advanced detection has attracted rising attention. However, the combination of compatible camouflage and radiative heat dissipation for space satellite still remains challenging, which requires low visibility and selective thermal emission in a dark and deep cold background. In this work, a dual dielectric Ge/SiO2 layer embedded Fabry-Perot multilayer film (W/Ge/SiO2/W/SiO2) is proposed for space stealth and heat dissipation. Ge and SiO2 films with appropriate thickness are designed to realize high visible absorption and spectra selective IR emission, simultaneously. The optimized multilayer film achieves a high absorbance (α = 0.983) in visible light (0.38–0.80 μm) for visible stealth, low emissivity (ε3–5 μm = 0.038; ε8–14 μm = 0.200) in atmospheric windows for infrared stealth, and relative high emissivity outside the atmospheric windows (ε5–8 μm = 0.487) for radiative heat dissipation. The simulation results indicate that the coupling of tunneling effect in ultrathin metallic W film and Fabry-Perot resonant is the main contribution to the excellent absorptivity and emissivity tunability. The proposed dual spacers embedded Fabry-Perot multilayer film paves a new way for multispectral camouflage of space satellite and other applications such as solar-thermal conversion, thermal management, energy saving, and detective technologies.

Multi-band compatible camouflage enabled by phase transition modulation of flexible GST films

With the rapid development of detection technology, there is an urgent need for multi-band compatible camouflage technology, particularly in the visible-infrared band. However, the conflicting requirements between camouflage across different bands and surface thermal management pose significant challenges in achieving synchronized control for multiple bands in diverse application environments and targets. Herein, we propose a spectrally selective emitter leveraging phase-change modulation of Ge2Sb2Te5, capable of achieving effective camouflage in both the visible band and two atmospheric windows over a wide temperature range. The designed emitters exhibit colorful appearances, compatible with various background environments, thereby ensuring the visible camouflage. Meanwhile, the emitters demonstrate low emissivity values of 0.1 in the MWIR band and 0.08 in the LWIR band, effectively reducing the infrared emission through atmospheric windows. The radiative temperatures of the optimized emitters in the MWIR and LWIR bands are reduced by 105°C and 140°C relative to the target surface (200°C), respectively, providing excellent radiative suppression compared to similar studies. Remarkably, the designed emitter still demonstrates robust flexibility, making it suitable for a variety of targets with complex curved surfaces. This work paves the way for designing the flexible visible-infrared compatible camouflage coatings with integrated thermal management functionality.