The photoluminescence (PL) mechanisms of as-grown GaInNAs/GaAs quantum well were investigated by tempera tu re-dependent PL measurements. An anomalous two-segmented trend in the PL peak energy vs. temperature curve was observed, which has higher and lower temperature-dependent characteristics at low temperature (similar to5-similar to80 K) and high temperature (above similar to80 K), respectively. The low and high-temperature segments were fitted with two separate Varshni fitting curves, namely Fit-low and Fit-high, respectively, as the low-temperature PL mechanism is dominated by localized PL transitions while the high-temperature PL mechanism is dominated by the e1-hh1 PL transition. Further investigation of the PL efficiency vs. 1/kT relationship suggests that the main localized state is located at similar to34 meV below the e1 state. It is also found that the temperature (similar to80 K) at which the PL full-width at half-maximum changes from linear trend to almost constant trend correlates well with the temperature at which the PL peak energy vs. temperature curve changes from Fit_low, to Fit_high. (C) 2004 Elsevier B.V. All rights reserved.