The role of Si dangling bonds (Pbcenter) on the broad luminescence band around 1.1 eV of porous Si is discussed, based on transient wave form measurement of optically detected magnetic resonance. The observed wave form is compatible with the nongeminate shunt path scheme and the characteristic time constant of this nonradiative process is deduced to be 15 &mgr;s at 1.6 K, whereas the competing radiative channel has a shorter decay time of 3 &mgr;s. Therefore,Pbcenters are unlikely to be involved as a radiative state in this infrared luminescence. Results are also discussed in conjunction with the visible luminescence process. ©1995 American Institute of Physics.