How to distinguish scattered and absorbed light from re-emitted light for white LEDs?

We have studied the light transport through phosphor diffuser plates that are used in commercial solid-state lighting modules (Fortimo). These polymer plates contain YAG:Ce+3 phosphor particles that scatter, absorb and re-emit incident light in the visible wavelength range (400-700 nm). To distinguish scattered from re-emitted light we used a narrowband light source. The re-emitted light is Stokes shifted to the red with respect to the scattered light, and is then spectrally separated from the scattered light. By using this technique we have measured the diffuse transmission of the phosphor diffuser plates. We use diffusion theory to extract the transport mean free path ltr over the full wavelength range. Simultaneously, we determine the absorption mean free path labs in the wavelength range 400 to 530 nm where YAG:Ce+3 absorbs. The measured absorption (1/labs) spectrum provides information about optimal design parameters: thickness of the plates and phosphor concentration of white LED