Temperature-dependent micro-photoluminescence (mu-PL) spectra and the spectral response for the 30-period undoped InAs/GaAs quantum-dot infrared photodetectors (QDIPs) are investigated. The competition of different transition levels within the spectra is observed. Also observed is the influence of dot size and density on the mu-PL characteristics. Consistently, the mid-infrared spectral response for the fabricated QDIPs exhibit the same energy position as the shifted PL spectra relative to the energy of wetting layer, which indicates the multi-transition mechanisms responsible for the QDIP spectral response. (c) 2005 American Vacuum Society.