On the elimination of the polarization bias of the luminescence or transient absorption of photoexcited isotropic solutions.

The photoluminescence from isotropic solutions and the light absorption by photogenerated species in isotropic solutions are in general partially polarized. In the case of electric-dipole transitions, the polarization bias can be represented as the product of a sample-dependent factor and a geometrical factor G for arbitrary experimental arrangements; G depends only on the orientation of the polarizers in the excitation beam and in the luminescence beam. G = 0 is a sufficient condition for the elimination of the polarization bias. The formalism is extended to unpolarized excitation and/or detection. The condition G = 0 is independent of ground-state depletion due to polarized or unpolarized excitation. The rotation of monochromators is introduced as a new experimental parameter. All known experimental configurations are treated in a systematic way. New configurations are proposed for surface excitation and for a quantum counter. The main results apply also to transient-absorption spectroscopy