The external photoluminescence quantum yield of, for example, thin fil
m semiconductors can be conveniently determined using the improved int
egrating-sphere method (see Figure) presented here. Spectrally resolve
d detection allows the excitation source and the emission to be distin
guished. The method will be particularly useful for samples with small
Stokes' shifts or low photoluminescence quantum yields or for highly
scattering samples.