The basic pathways of heat exchange are conduction, convection, and radiation. To effectively dissipate heat, people often reduce the thermal resistance of the heat flow path and enhance the convection coefficient, often neglecting thermal radiation. LED lamps generally use natural convection for heat dissipation. The heat sink quickly transfers the heat generated by the LED to the surface of the heat sink. Due to the low convection coefficient, the heat cannot be dissipated into the surrounding air in time, leading to an increase in surface temperature and a deterioration of the LED's working environment. Increasing emissivity can effectively remove heat from the heat sink surface through thermal radiation. Aluminum heat sinks typically increase surface emissivity through anodizing. Ceramic materials themselves possess high emissivity characteristics, eliminating the need for complex post-processing.
Radiation Mechanism The radiation mechanism of ceramic materials is generated by the non-resonant effects of random vibrations of two-phonons and multi-phonons. High-emissivity ceramic materials such as silicon carbide, metal oxides, and borides exhibit extremely strong infrared-activated polar vibrations. These polar vibrations possess strong anharmonic effects, resulting in absorption coefficients in their dual-frequency and super-frequency regions typically on the order of 100–100 cm⁻¹. This corresponds to the low reflectivity of the remaining reflection band in the medium-intensity absorption region, thus favoring the formation of a relatively flat, strong radiation band.
Generally, radiation bands with high thermal radiation efficiency extend from the strong resonant wavelength to the entire two-phonon combination and super-frequency region in the shortwave range, including some multiphonon combination regions. This is a common characteristic of the radiation bands of most high-emissivity ceramic materials. It can be said that strong radiation bands primarily originate from two-phonon combination radiation in this wavelength band. With a few exceptions, the radiation bands of general radiative ceramics are concentrated in the two-phonon and three-phonon regions greater than 5 m. Therefore, for infrared radiative ceramics, radiation in the 1–5 m wavelength band mainly originates from in-band transitions of free charge carriers or direct transitions of electrons from impurity energy levels to the conduction band, while radiation in the wavelength band greater than 5 m is mainly attributed to two-phonon combination radiation.
