A recently developed thermal lens spectrometry configuration has been used to study CdSe/ZnS core-shell quantum dots (QDs) suspended in toluene and tetrahydrofuran (THF) solvents. The special features of this configuration make it very attractive to measure fluorescence quantum yield (η) excitation spectrum since it simplifies the measurement procedure and consequently improve the accuracy. Furthermore, the precision reached is much higher than in conventional photoluminescence (PL) technique. Two methods, called reference sample and multiwavelength have been applied to determine η, varying excitation wavelength in the UV-visible region (between 335–543 nm). The η and PL spectra are practically independent of the excitation wavelength. For CdSe/ZnS QDs suspended in toluene we have obtained η=76±2%. In addition, the aging effect on η and PL has been studied over a 200 h period for QDs suspended in THF.