The excitation power and temperature dependences of photoluminescence (PL) emission in 6H polytype of silicon carbide are investigated extensively. A sublinear power-function dependence of the donor-acceptor pair emission intensity on the excitation power is explained by a rate-equation model. A very low power exponent (k = 0.3) in a power-law dependence of PL intensity on the excitation power of B-N codoped 6H-SiC at room temperature indicates that three-particle Auger recombination is the main carrier recombination pathway. Auger recombination in an Al-N codoped SiC does not manifest as strongly as that of the B-N codoped sample due to high density of ionized impurities which capture the nonequilibrium carriers faster. The ionized impurities form localized potential wells due to their random distribution, which is revealed by a blue shift of the PL band with increasing excitation intensity (approximately 16 meV per decade) and with decreasing temperature. Low-temperature Hall-effect measurement of the Al-N codoped sample confirms the high density of ionized impurities and significantly reduced ionization energy of dopant states by approximately 53 meV due to the high dopant densities. These results could lead to realization of tunable SiC-based light sources in severe operating conditions.