Thermal quenching of luminescence of Er dopants in Si nano-crystals (Si-nc’s) was investigated employing an impedance model for the analysis of photo-injected charges. Relaxation response indicated that Er doping forms not only optical centers but also trapping centers near the Si-nc’s. The response time constant of trapped charges was dependent on temperature, with the dependence correlating to thermal quenching. These findings indicate that quenching occurs by trapping followed by consumption of charges. The complex analyses revealed that the response represents non-radiative recombination at the centers rather than release of confined charges from the Si-nc through the centers. We propose a possible energy diagram for the non-radiative recombination.