The mid-infrared (MIR) spectral window, typically spanning wavelengths from 2.5 to 20 μm (or wave numbers 500-4000 cm-1), constitutes a pivotal domain of the electromagnetic spectrum, where molecular vibrational and rotational transitions enable precise spectroscopic identification and tunable thermal radiation modulation. Mastery over this spectral range underpins a broad and growing suite of technologies, encompassing high-resolution MIR imaging and spectroscopic gas sensing, advanced thermal management via radiative cooling/heating and dynamic emissivity control, integrated photonic platforms featuring low-loss optical windows and waveguides, as well as MIR laser systems that leverage broadband transparency for efficient frequency conversion and beam delivery. High MIR transmittance (TMIR) is therefore essential for driving MIR photonic innovations, enabling efficient photon transmission, modulation, and targeted heat control. Yet, the fundamental interplay among material structure, photonic/electronic behavior, and MIR optical performance remains underexplored. This review comprehensively evaluates high TMIR materials, with an emphasis on their optical mechanisms, structural attributes, synthesis routes, and performance benchmarks. By elucidating structure-property relationships and offering design strategies for MIR transparency, this review provides a roadmap for developing high-performance MIR transparent materials for advanced thermal management, infrared optics, and next-generation photonic systems.
Zhang et al. (Sat,) studied this question.