The thermo-optical properties of CdSe/ZnS core–shell quantum dots (QDs) embedded in organic/silica hybrid colloids (organic/silica sols) were measured using the thermal lens (TL) technique. GPTS/TEOS-derived organic/silica hybrid colloids were prepared by a sol–gel method from the hydrolysis reaction of 3-glycidoxypropyltrimethoxysilane (GPTS) and tetraethylorthosilicate (TEOS) alkoxides. TL transient measurements were performed to study the effect of the CdSe/ZnS QDs (with three different sizes ∼ 2.4, 2.9 and 4.4nm) embedded in GPTS/TEOS-derived organic/silica sols. The thermal diffusivity, the fraction thermal load and the radiative quantum efficiency (η) were determined. Fluorescence measurements corroborate the TL results and high η values were obtained.