Rapid emision from bulk thermal sources is usually seems to be disjointed and broadband. But the presence of micro on the surface of thermal sources, the radiative characteristics can be greatly altered. To give the theoretical explanation, you have to understand mathematical terms such as modeling and simulation (use of matrices with transfer and domain) processes. One can also bring in numerical approach using finite Runge kutta method of second order. With that, one can easily explain the narrow band emission of emitter

ieeexplore.ieee.org/document/7523958/