High Thermal Emittance Research Articles

Solar-Adaptive Cooling Blocks Composed of Recycled Fabric.

Radiative cooling technologies have had a significant impact on advancing carbon neutrality efforts by significantly improving the passive cooling efficiency. The tandem of conduction and radiation enables solar-adaptive radiative cooling through the insulating effect of materials along with solar absorption, which affects the thermal state of materials and enhances radiative thermal transfer from the surface under solar irradiation. This enhancement is achieved by utilizing the porous polymeric structure of materials, which facilitates improved conduction pathways along with solar reflectance, while maintaining the effective emission of thermal radiation. In this particular scenario, blocks, which were made of recycled fibers, offer a great opportunity as solar-adaptive cooling materials, enabling their easy deployment for cooling applications. Herein, we have fabricated a porous block using fiber wastes that combines strong solar reflectance (92%) at the 1 μm region and high thermal infrared emittance (∼75%) at the 10 μm region. The combination of effective solar reflection and thermal infrared emission allows the fiber block to achieve a high cooling performance of approximately 68 W/m2 under solar irradiation. In addition, the fiber block works effectively for insulation during the night, thereby enhancing its heat retention capabilities. The economic and environmental advantages of the fiber block make it a cost-competitive and sustainable choice for near-market cooling technologies. This design is anticipated to expand the practical application range of passive cooling.

FIELD EVALUATION OF THE EFFICACY OF PASSIVE RADIATIVE COOLING INFRASTRUCTURE: A CASE STUDY IN PHOENIX ARIZONA

Radiative properties of shade structures affect their surface temperatures, sensible heat fluxes and longwave and shortwave radiation exchange. In fact, structures with high solar reflectance and thermal emittance have the potential to remain below ambient air temperatures, convecting sensible heat from the air to the surface and then radiating that heat to space—a sort of radiant heat pump.We explore cooling benefits of urban surfaces with high solar reflectance and high thermal emittance radiative cooling films through a field measurement campaign in Phoenix Arizona, USA. The tested films have solar reflectance and selective thermal emittance (in wavelengths 8-13 μm) close to 95%. We applied films in both before-after and control-test experimental designs on thin metal roofs of park shade structures. We measured surface temperatures, surface heat fluxes, upward- and downward-welling longwave and shortwave radiation, and local weather conditions.Results demonstrate the ability of radiant cooling films to reduce surface temperatures on hot days below ambient air temperatures. Test surfaces with cooling films were an average of 7°C cooler than control shelter surfaces over the diurnal cycle, reducing sensible heat fluxes into the environment by up to 80%, and lowering mean radiant temperatures for pedestrians using the shelters by more than 3°C. It was also observed that the sum of the net reflected shortwave and emitted longwave radiation over the diurnal cycle can exceed the total incident longwave and shortwave radiation on the surface, demonstrating the ability of these materials to radiatively “pump” heat out of the city.

Influence of the flame jet on heat loss and thermal efficiency of lean burn pre-chamber natural gas engine with various geometrical combustion chambers

Due to relatively high thermal efficiency and low NOx emission, the pre-chamber type lean burn natural gas engine for cogeneration is expected to be spread rapidly in the near future. To offer a guidance for designing the pre-chamber natural gas engines, in the present study, the influence of the flame jets on combustion process and thermal efficiency of pre-chamber type lean burn natural gas engine was investigated with various pre-chamber orifice diameters and angles and piston bowl shapes by numerical simulation. The presented results showed that when the orifice diameter is smaller, it results in higher heat loss with the stronger gas flame jets impinging on piston top and cylinder liner walls, but the higher degree of constant volume heat release can be also obtained. Consequently, there is no significant difference in the thermal efficiency for these four orifice diameters. Increasing the angle of the orifice and the depth of the piston bowl can avoid the heat loss caused by the early impact of flame jets on the piston top wall. In addition, compared to the diameter of piston bowl, the depth of piston bowl, which is related to the distance from the orifice to the piston bowl, should have more effect on the combustion process and thermal efficiency. For wider orifice angle, the heat loss was also increased, particularly to cylinder head. Finally, the optimal thermal efficiency obtained by balancing heat loss and the degree of constant volume heat release is 44.73%.

Synthesis and evaluation of thermal and optical properites of Fe2AlB2 phase alloy for thermal control in space applications

Ternary laminated Fe2AlB2 alloy holds its significance in displaying high strength, damage tolerance, oxidation and radiation cracking resistance. It is synthesized through a pressureless sintering route from elemental powders. Synthesis of Fe2AlB2 is studied from two different molar ratios (2/1/2 and 2/1.5/2) and three different sintering temperatures (1100°C, 1150 °C and 1200 °C). Phase analysis is carried out through an x-ray diffractometer and scanning electron microscopy (SEM). In addition, thermal decomposition, thermal conductivity and absorbance spectra are examined. Fe2AlB2 begins to decompose at 1169 °C into borides and aluminides. Thermal conductivity and diffusivity of Fe2AlB2 decreases with increase in temperature. Lower solar reflectivity and high thermal emittance of Fe2AlB2 implies the thermal control and optical behavior that can be expected for extreme space environments.

Epsilon-near-zero thin films in a dual-functional system for thermal infrared camouflage and thermal management within the atmospheric window.

Thermal infrared camouflage aims to reduce the detectability of a target using thermal imaging devices. Given the typically high thermal emissivity in everyday environments, the thermal emissivity of the background environment must be considered. The conventional low-emissivity strategy for thermal camouflage is only effective for targets at extremely high temperatures (>350 °C), making it unsuitable for applications near room-to-medium-high temperature range (<350 °C). In this study, we introduce metallic glass into infrared thermal camouflage technology, exploiting its adjustable emissivity to accommodate diverse infrared thermal camouflage scenarios. Moreover, we combined metallic glass with the Berreman mode of epsilon-near-zero (ENZ) thin films (SiO2, Al2O3, and TiO2) for the first time. In the long wave infrared (LWIR, 8-14 μm) regions, the small viewing angle exhibits the optical properties of metallic glasses, while the large viewing angle (above 45°) provides high thermal emissivity in transverse-magnetic (TM) polarization. A thermal management function was provided without affecting the thermal camouflage performance. The cooling power exhibited by ENZ thin films on metallic glass surpassed that of the conventional low-emissivity strategy for thermal camouflage by a factor of 1.79. Furthermore, the thermal images indicated over 97% similarity in thermal radiation between the target and background environments. We developed a dual-function system for infrared camouflage and thermal management within an identical wavelength region of the atmospheric window.

Solar to Thermal Energy Conversion Potential of Carbon Nanotubes Modified Copper Oxide Nanocomposite Thin Film Solar Selective Absorbers

AbstractCarbon nanotubes modified copper oxide nanocomposite (CNTs–CuO NC) selective absorbers were prepared through a sol‐gel method by varying weight percentage of CNTs and coated on aluminum (Al) substrates using a dip coating technique to form thin films (TFs). The surface morphology of CNTs–CuO NC TF examined by scanning electron microscopy disclosed linear arrangement of CNTs–CuO NC TF with average particle diameter of 200±30 nm. The X‐ray diffractometer analysis of the CNTs–CuO NC TF revealed the presence of CuO in monoclinic crystal structure. Moreover, the X‐ray diffractometer analysis disclosed good crystalline quality of the CNTs–CuO NC TF and average crystallite size of the CuO and CNTs–CuO NC TF was found to be 69.38 and 85.94 nm, respectively. The energy dispersive X‐ray spectrum of CNTs–CuO NC TF ascertained the presence of Cu, O and C elements with atomic weight proportion of 71.07, 21.61 and 7.32 %, respectively. The functional groups investigation by FTIR spectroscopy exhibited distinct spectral features of CNTs and the peaks observed at 516.78 and 588.70 cm−1 correspond to the characteristic vibrations of metal‐oxygen (M−O) bond that indicates the presence of CuO in the hybrid CNTs‐CuO NC TF. The optical property of the CNTs–CuO NC TF with CNTs weight proportion of 0.5 % inspected through UV‐Vis‐NIR spectroscopy exhibited high solar absorptance and thermal emittance values of 85.9 and 4.3 %, respectively. The observed highest solar selectivity value of 19.98 suggests that the CNTs–CuO NC TF coating can be apparently used as solar selective absorber.

Optimization of Dielectric-Metal Multilayer Structure for Color-Preserving Radiative Cooling Window.

Radiative cooling window has been designed to emit infrared radiation in the atmospheric transparency window and reflects near-infrared light while allowing visible light to pass through. However, improvements are still needed in the transmissivity of visible light, the reflectivity of near-infrared light, and emissivity of mid-infrared spectra. This paper proposes a color-preserving radiative cooling window consisting of a multilayer film as a transparent near-infrared reflector and polydimethylsiloxane (PDMS) as a thermal emitter. This design involves optimizing the types of film materials, the number of layers, and the thicknesses of the films through a genetic algorithm. The performance of multilayer films with various layer numbers is compared, and we choose 7-layer multilayer film (Al2O3/Ag/Al2O3/Ag/Al2O3/Ag/Al2O3) as the transparent near-infrared reflector. Then, we analyze its spectral characteristics in depth. Sequentially, we place a 100-μm-thick PDMS as a thermal emitter above the transparent near-infrared reflector. By combining the transparent near-infrared reflector with the PDMS and utilizing genetic algorithm, a color-preserving radiative cooling window has been achieved with flat and broadband average visible transmittance (86%), high average near-infrared reflectance (86%), high average thermal emissivity (95%) in the atmospheric window, and the drop of temperature (22.3, 21.2, and 15.8 K when nonradiative heat coefficient is, respectively, 0, 6, and 12 W/m2/K).

A systematic analysis of energy-saving potential of spectrum-selective radiative cooling materials in buildings

Passive cooling of buildings through radiative cooling (RC) is considered an effective method for reducing the energy consumption of air conditioning. In recent years, spectrum-selective RC materials (RCMs) have received extensive attention owing to their low solar absorptivity and high thermal emissivity in the atmospheric window. The energy-saving performance of RCMs is related to their own properties and local meteorological conditions, building type, building form, and energy use patterns. Although several studies have explored the performance of RCMs, most existing studies have considered a single building type and meteorological condition, and simple building forms that differ significantly from real buildings. Hence, the application analyses of RCMs to buildings are not sufficiently comprehensive. This study focused on the energy-saving potential of RCMs for building applications, and presented a systematic framework to analyze the energy-saving potential of RCMs under different conditions. DeST, which is embedded with a long-wave radiative heat transfer calculation module based on the equivalent sky temperature, was adopted as the simulation software. It can accurately calculate the radiative heat transfer in different wavelength bands, thus making the simulation results more accurate. Based on the calculation results of large-scale cases considering four major factors, namely climate, building type, construction year, and installation location of RCMs, the energy-saving performance of RCMs in different cases was analyzed, and the return on investment is performed, and more comprehensive suggestions were provided for applying RCMs in future buildings.

Fluorescence‐Enabled Colored Bilayer Subambient Radiative Cooling Coatings

AbstractPassive daytime radiative cooling has emerged as a promising green technology for the thermal management of buildings, vehicles, textiles, and electronics. Typically, both high solar reflectance and high thermal emissivity are prerequisites to achieve sufficient daytime cooling. However, colored radiative cooling materials are facing the dilemma of introducing visible light absorption, leading to challenges in balancing cooling and aesthetic demands. Here, three colored bilayer radiative cooling coatings, each comprised of a white base layer and a colored top layer with fluorescence enhancement are fabricated. Three phosphors (Sr2Si5N8:Eu2+, Y3Al5O12:Ce3+, and (Ba,Sr)SiO4:Eu2+) are employed with respective photoluminescence quantum yields (PLQYs) of 81%, 95.8%, and 91.0% as the colored pigment in the top layer. To mitigate the contradiction between coloration and solar reflectance, SiO2 microspheres are introduced into the top layer and utilize their Mie‐resonance‐based multiple scattering to increase the photoluminescent (PL) properties of the phosphors, which jointly boosts the effective solar reflectance (ESR) of the top layer. As a result, the three bilayer coatings exhibit soft colors while achieving subambient cooling with temperature drops of up to 1.5 °C. This fluorescence‐enhancement strategy may pave the way for preparing highly efficient radiative cooling coatings with tunable colors.

Metasurface with all-optical tunability for spatially-resolved and multilevel thermal radiation

Abstract Manipulating the thermal emission in the infrared (IR) range significantly impacts both fundamental scientific research and various technological applications, including IR thermal camouflage, information encryption, and radiative cooling. While prior research has put forth numerous materials and structures for these objectives, the significant challenge lies in attaining spatially resolved and dynamically multilevel control over their thermal emissions. In this study, a one-step ultrafast laser writing technique is experimentally demonstrated to achieve position-selective control over thermal emission based on the phase-change material Ge2Sb2Te5 (GST). Ultrafast laser writing technique enables direct fabrication and manipulation of laser-induced crystalline micro/nano-structures on GST films. Thermal emission can be precisely controlled by adjusting the pulse energy of the ultrafast laser, achieving a high thermal emissivity modulation precision of 0.0014. By controlling thermal emission, the ultrafast laser writing technique enables multilevel patterned processing. This provides a promising approach for multilevel IR thermal camouflage, which is demonstrated with emissivity-modulated GST emitters. Remarkably, ultrafast laser-induced crystalline micro/nano-structures display geometric grating features, resulting in a diffraction-based structural color effect. This study demonstrates the effective use of laser-printed patterns for storing information in both visible and infrared spectrum.

A durable, breathable, and weather-adaptive coating driven by particle self-assembly for radiative cooling and energy harvesting

The imperative to attain net-zero emissions emphasizes energy conservation. Radiative cooling stands out as a compelling technology in this pursuit for its self-sufficiency and cost-effectiveness. However, the radiative cooling faces the challenge in varied weather, including high ultraviolet (UV), cloudy and rainy days, primarily due to instability of radiative cooling materials and mono-energy conservation mechanism. To address this issue, a durable, breathable, and weather-adaptive coating (porous PTFE coating) has been developed through assembling polyfluortetraethylene (PTFE) nanoparticles enabled by the differential interaction in a binary-solvent system. The porous PTFE coating exhibits high solar reflectivity (94%) and thermal emissivity (93%), which results from the precisely tunable assembly of PTFE nanoparticles, forming a desired porous morphology. This design serves as effective scattering, achieving a sub-ambient cooling effect of approximately 5 ℃ at midday. With an outstanding UV protection factor (UPF) of 179.15, the porous PTFE coating sustained stability after 40 days exposure to solar radiation. Leveraging the porous PTFE coating's exceptional negative triboelectric effect, an engineered high-performance droplet electricity nanogenerator (DEG) achieves a notable power density of 153.8 mW/m2, revealing significant potential for raindrop energy harvesting on rainy days. The versatile porous PTFE coating, with its exceptional weather adaptation and UV stability, holds promise for diverse applications, advancing sustainable and efficient energy solutions with reliability in varying conditions.

High Thermal Conductivity and Radiative Cooling Designed Boron Nitride Nanosheets/Silk Fibroin Films for Personal Thermal Management.

The implementation of passive cooling strategies is crucial for transitioning from the current high-power- and energy-intensive thermal management practices to more environmentally friendly and carbon-neutral alternatives. Among the various approaches, developing thermal management materials with high thermal conductivity and emissivity for effective cooling of personal and wearable devices in both indoor and outdoor settings poses significant challenges. In this study, we successfully fabricated a cooling patch by combining biodegradable silk fibroin with boron nitride nanosheets. This patch exhibits consistent heat dissipation capabilities under different ambient conditions. Leveraging its excellent radiative cooling efficiency (Rsolar = 0.89 and εLWIR = 0.84) and high thermal conductivity (in-plane 27.58 W m-1 K-1 and out-plane 1.77 W m-1 K-1), the cooling patch achieves significant simulated skin temperature reductions of approximately 2.5 and 8.2 °C in outdoor and indoor conditions, respectively. Furthermore, the film demonstrates excellent biosafety and can be recycled and reused for at least three months. This innovative BNNS/SF film holds great potential for advancing the field of personal thermal management materials.

Strain-Insensitive Outdoor Wearable Electronics by Thermally Robust Nanofibrous Radiative Cooler.

Stable outdoor wearable electronics are gaining attention due to challenges in sustaining consistent device performance outdoors, where sunlight exposure and user movement can disrupt operations. Currently, researchers have focused on integrating radiative coolers into wearable devices for outdoor thermal management. However, these approaches often rely on heat-vulnerable thermoplastic polymers for radiative coolers and strain-susceptible conductors that are unsuitable for wearable electronics. Here, we introduce mechanically, electrically, and thermally stable wearable electronics even when they are stretched under sunlight to address these challenges. This achievement is realized by integrating a polydimethylsiloxane nanofibrous cooler and liquid metal conductors for a fully stable wearable device. The thermally robust architecture of nanofibers, based on their inherent properties as thermoset polymers, exhibits excellent cooling performance through high solar reflection and thermal emission. Additionally, laser-patterned conductors possess ideal properties for wearable electronics, including strain-insensitivity, nonsmearing behavior, and negligible contact resistance. As proof, we developed wearable electronics integrated with thermally and electromechanically stable components that accurately detect physiological signals in harsh environments, including light exposure, while stretched up to 30%. This work highlights the potential for the development of everyday wearable electronics capable of reliable operation under challenging external conditions, including user-activity-induced stress and sunlight exposure.

A wide angle broadband solar absorber with a horizontal multi-cylinder structure based on an MXene material.

An MXene material absorbs visible and IR light which makes a MXene-based solar absorber an ideal absorber. Here, we propose a high-absorption broadband absorber based on an array of MXene composite cylinder ring structures. The structure designed in this article fully utilizes the MXene material's large surface area to volume ratio, and in the wavelength range of 300-5000 nm, the average absorption efficiency is as high as 98.44%, and the energy absorption rate in the AM 1.5 solar radiation spectrum is 98.76%. The absorption characteristics of the absorber are analyzed by using the finite-difference time-domain (FDTD) method. The electric and magnetic field patterns indicate that the high absorption performance is attributed to the coupling effect of surface plasmon resonance and gap surface plasmon resonance. Furthermore, the absorber exhibits insensitivity to the polarization angle and demonstrates high absorption efficiency even at large incidence angles. Within a certain manufacturing tolerance range, the absorber can still maintain its broadband absorption characteristics. The absorber also shows a high thermal emissivity of 98.5% when the temperature is 1750 K. The findings offer a theoretical foundation for the development of absorption metamaterials for solar energy harvesting elements.

Investigation of a high-performance solar absorber and thermal emitter based on Ti and InAs

In this work, we utilized Ti and InAs materials to design a device capable of perfect solar absorption and high thermal emission efficiency. This structure is capable of generating surface plasmon resonance (SPR) and cavity resonance (CR).

Hierarchically structured passive radiative cooling ceramic with high solar reflectivity.

Passive radiative cooling using nanophotonic structures is limited by its high cost and poor compatibility with existing end uses, whereas polymeric photonic alternatives lack weather resistance and effective solar reflection. We developed a cellular ceramic that can achieve highly efficient light scattering and a near-perfect solar reflectivity of 99.6%. These qualities, coupled with high thermal emissivity, allow the ceramic to provide continuous subambient cooling in an outdoor setting with a cooling power of >130 watts per square meter at noon, demonstrating energy-saving potential on a worldwide scale. The color, weather resistance, mechanical robustness, and ability to depress the Leidenfrost effect are key features ensuring the durable and versatile nature of the cooling ceramic, thereby facilitating its commercialization in various applications, particularly building construction.

Sorbent-coupled radiative cooling and solar heating to improve atmospheric water harvesting

Atmospheric water harvesting (AWH) technology is a promising technology for addressing global water shortages and contributing to social development. Current AWH technologies, including fog collection, dew collection, and sorption-based AWH mostly focus on a single water harvesting mechanism, and this can limit their working conditions and overall performance. In this work, a composite hydrogel with a low phase change enthalpy of water (1695 kJ kg−1) was coupled with radiative cooling and solar heating to improve passive AWH performance and working conditions. High thermal emittance ε¯LWIR = 0.98 and solar absorptance α¯solar = 0.93 were achieved for radiative cooling in the nighttime and solar heating in the daytime. During the night, radiative cooling could improve the water capture rate from 0.242 kg m-2h−1 (i.e., only sorbent) to 0.310 kg m-2h−1 (i.e., sorbent-coupled radiative cooling) in the outdoor experiment. In the daytime, solar interfacial evaporation improved the water release rate to 1.154 kg m-2h−1. Effects of meteorological parameters, such as relative humidity, ambient temperature, and solar intensity were also discussed theoretically and experimentally. It is indicated that the designed passive AWH device can work over a wide range of meteorological parameters. The outdoor all-day experiment indicated that the maximum water harvesting can be 2.04 kg m−2 in a cycle work. This demonstrates that sorbent-coupled radiative cooling and solar heating provide a potential approach for future solar-driven AWH systems.

Achieving thermochromic upconversion of Tm3+ for high-sensitive nanoprobe and information encryption

Upconversion-based optical thermometry has many merits, such as quick temperature response, higher thermal sensitivity and robust reliability. However, the previous works were mainly focused on the thermally coupled emissions, limiting their thermal sensitivity due to the intrinsic constraint by small energy gaps (e.g., <2000 cm−1) according to Boltzmann distribution theory. Here, we report a design of NaYF4:Yb3+/Tm3+@NaYF4 core-shell nanostructure to achieve thermochromic upconversion and high thermal sensitivity by taking advantage of nonthermally coupled upconversion emissions of Tm3+. We show that the blue upconversion emission of Tm3+ at 475 nm (1G4→3H6) exhibits a regular decrease with elevating temperature, while its deep-red emission at 696 nm (3F2,3→3H6) presents an increase. Such a feature leads to a rapid rise of luminescence intensity ratio (I696 nm/I475 nm) and the optimal relative sensitivity (Sr) reaches 2.79 % K−1 (503 K). More interestingly, the sample gives rise to a gradual emission color change from blue to purplish-red with lifting temperature. Our results offer a new class of upconversion-based nonoprobe with high thermal sensitivity and observable emission color variation, showing a great potential for nanoprobe and information security.

The synthesis and luminescence properties of Bi3+/Eu3+ co-doped Gd2O3 phosphors with high thermal stability and tunable emission via energy transfer

In this work, the highly monodisperse (Gd0.99-xBi0.01Eux)2O3 phosphors with spherical morphologies (∼170 nm) are successfully obtained through precursor synthesis via urea-based homogeneous precipitation (UBHP) method, followed by annealing at 1000 °C. The Bi/Eu-doped does not alter the crystal structure, and maintain the cubic structure of the Gd2O3 host. Owing to the Bi3+ occupies two different sites (C2, S6) in Gd2O3 of the cubic phase, the 1S0 → 3P1 transition of Bi3+ has two significant excitation bands (335 nm and 375 nm). By monitoring the excitation at 335 nm and 375 nm, the (Gd0.99-xBi0.01Eux)2O3 phosphors show both Bi3+ (420 nm and 530 nm) and Eu3+ (611 nm) emissions, respectively. The presences of Gd3+ and Bi3+ excitation bands on the PLE spectra by monitoring the Eu3+ emission indicate the Bi3+ → Eu3+ and Gd3+ → Eu3+ energy transfer, respectively, and the energy transfer efficiency is up to 99 %. Meanwhile, the energy transfer mechanism of the (Gd0.99-xBi0.01Eux)2O3 samples is dominated by the dipole-dipole interaction. Under two different excitation wavelengths, the emission intensity varies with the Eu3+ doping content and the quenching concentration is about 3 at%. The calculated value of the critical distance Rc is 12.12 Å, which indicates that the quenching mechanism is mainly caused by the multipole interaction. Meanwhile, the emission color can be tuned though adjusting the Eu3+ content. The temperature-dependent (in the range of 100–500 K) analysis has been obtained, the results indicate the (Gd0.99-xBi0.01Eux)2O3 samples have good thermal stability. The (Gd0.99-xBi0.01Eux)2O3 phosphors developed in this work is expected to be widely used in lighting and optical display applications.

Ultra‐Emissive MgO‐PVDF Polymer Nanocomposite Paint for Passive Daytime Radiative Cooling

AbstractPassive daytime radiative cooling (PDRC) holds enormous potential to provide low‐cost, electricity‐free cooling in hot environments and to overcome the urban heat island effects. Conventional radiative cooling devices consist of complicated multilayer structure, and reflective back metallic plates that are unsuitable for household applications. Most single‐layer polymer nanocomposites are also not practically applicable due to their high cost, frailty, and sub‐optimum cooling performances arising from low thermal emissivity. Herein, it is shown that ultra‐white and ultra‐emissive magnesium oxide (MgO)‐polyvinylidene fluoride (PVDF) nanocomposite that exhibits an average ≈7°C temperature decrease below the sub‐ambient conditions under direct sunlight. The optimized MgO‐PVDF metamaterials with a dielectric particle size of ≈50 nm exhibit a large solar reflectance of 96.3% due to the Mie‐scattering and a record high thermal emission of 98.5% at the atmospheric transmission window due to the anharmonic multiphonon Mg─O bond vibrations, and other stretching/bonding vibrations from the polymer. The nanocomposite paint exhibits water‐resistant hydrophobic properties and can be easily coated on pavers, wood sticks, etc., with high uniformity and good adhesion. This work provides a low‐cost, scalable, and solution‐processed nanocomposite coating with excellent cooling performance for pavers, tiles, and building cooling applications, especially in equatorial regions, southeast Asia, middle‐east, and African regions.