Gong Hao,Wang Zhongyang,Song Xiaokun,Li Hongchao,Sun Kai,Zhou Xiao,Fan Tongxiang
Effective radiative cooling is crucial for reducing undesirable energy consumption caused by thermoregulation technology. However, conventional passive coolers still suffer from challenges such as vulnerability to harsh service conditions and suboptimal radiative cooling performance without guidance from optical design. Metacoating based on photonic structure design and all-inorganic components can overcome these drawbacks. In this paper, we fabricate a metacoating for radiative cooling, incorporating zirconia submicrospheres (ZS) within a potassium silicate binder. ZS with optimal diameters of about 500 nm were synthesized to efficiently scatter sunlight. The metacoating has a solar absorption ( α s ) of only 0.04 in the 0.25–2.5 µm range, and an infrared emittance ( ε ) of 0.91 in the 2.5–16.7 µm range. The low solar absorption is attributed to the high backscattering efficiency of ZS and their high-volume fraction, as confirmed by Mie scattering theory and Monte Carlo ray-tracing simulations, while the high emittance is driven by vibrational absorption from chemical bonds in ZS and potassium silicate. After proton and electron irradiation, the metacoating retains α s below 0.083 and ε above 0.910, indicating excellent irradiation resistance. Our findings highlight that metacoating utilizing ZS with a large bandgap and suitable diameters holds significant potential for advancing space radiative cooling technologies.
Space exploration is inseparable from advanced antiradiation materials with exceptional properties. Among these, nonlinear optical materials and devices, such as irradiation-resistant saturable absorbers (SAs), have garnered significant attention, particularly due to their critical role in integrated photonics for space use. This study presents a comprehensive evaluation of the space adaptability of two-dimensional (2D) W2N3 under simulated space radiation conditions. When subjected to 60Co γ-ray irradiation at doses exceeding 45 years of accumulation in a typical low-Earth orbit, W2N3 retained its robust third-order nonlinear saturable absorption across the visible- to near-infrared spectral range. Femtosecond transient absorption spectra offer a comprehensive view of the carrier dynamics of W2N3 before and after irradiation, delving into radiation effects and damage mechanisms that are otherwise elusive to conventional techniques. The synthesized W2N3 nanosheets were successfully employed as efficient SAs for Q-switched mode-locking in a Yb-doped fiber laser. The laser system operated at ∼1 μm NIR with high pulse energy and low saturation power, highlighting the remarkable potential of W2N3 for integration into lasers, modulators, and other photonic devices. Notably, the irradiated W2N3 demonstrated an identical mode-locking performance compared to its pristine counterpart. These findings provide valuable guidance for the rational design and screening of nonlinear optical materials capable of withstanding space radiation, offering significant implications for future space-based photonic applications.
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