semiconductor colloids were investigated. The absorption spectra of BiI
3
colloids and I
2
-alcohol solution were compared. It is verified that the absorption of BiI
3
ultra-fine particles is covered by the strong absorption of I
3
-
ion. In the emission spectra of BiI
3
colloids
the luminescence due to hexadecyl-pyridine was observed. Because of energy transfer between surface of BiI
3
micro-crystals and hexadecyl-pyridine
we observed the absorption of BiI
3
microcrystals by measuring the excitation spectra. The size distribution calculated by measured data is in good agreement with theoretical one. The experimental results indicate that there exist profound quantum size effects in BiI