From the imgae you shared, I am assuming you are already defining these internal surfaces as interface surfaces. To learn more about interface surfaces, please refer to the user manual page.
May I know the fluent version you are using. If you are using older version, you will find option to input internal emissivty under thermal boundary condition. I assume you are using DO radiation model. Correct me if I am wrong.
Please refer to the user manual guide 5.3.6. Discrete Ordinates (DO) Radiation Model Theory (ansys.com)
section :
5.3.6.6. Boundary and Cell Zone Condition Treatment at Opaque Walls and
5.3.6.7.1. Semi-Transparent Interior Walls
To learn how absorption, transmission and refelction is acconted in DO raditaion model. You will have to input emissivity, absorption coefficient, refractive index and diffuse fraction etc for the same.
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