Size effect of thermal radiation

Size effect of thermal radiation is investigated as a function of particle size and temperature. When the size of the particle becomes small, the maximum wavelength of the thermal emission is order of the size, so the spectrum of the thermal emission becomes different compared to well-known blackbody radiation. We calculate the energy density by considering the dimension of the particle. The thermal radiation can be approximated to Wien's law in high frequency range when the size of particle becomes small. The energy density is shown as a function of particle size at a constant temperature. The energy density is also shown as a function of temperature at a constant size.