Based on coupled quantum electrodynamics the light propagation in active silicon nanocrystals was reported in this paper. The classical electron oscillator model was employed to bridge the link between the rate equations of the four-level atomic system of the active medium and the electromagnetic interaction. With the assistance of auxiliary differential equations we numerically solved the system by using the Finite-difference Time-domain (FDTD) method. Both stimulated and spontaneous emissions were taken into account in the active medium system. Light amplification characteristics due to stimulated emission were investigated under various pumping rates. To enhance the spontaneous emission, microcavities based on one-dimensional photonic crystals were designed to maximize the nonlinear interaction between the active medium and electromagnetic waves. Preliminary experimental investigation of the cavity-enhanced luminescence was performed to demonstrate the validation of the proposed simulation scheme.