Excitation-power-dependent spectral shift in photoluminescence in dye molecules in strongly scattering optical media

Photoluminescence spectra and the reflectivity of incident light were exami ned in dye molecules in strongly scattering media. With increasing incident light intensity, the spectra show red- and blueshifts depending on the geo metry of experiments, and the reflectivity increases nonlinearly. These exc itation-power-dependent spectral shifts and nonlinear reflectivity are well explained when we consider saturation absorption in the excitation process and the reabsorption in the luminescence process in dyes. [S0163-1829(99)1 4701-5].