Cadmium selenide (CdSe) quantum dots are chemically synthesized in the diameter ranges of 2 to 6 nm. These colloidal solutions are excited with a blue laser of wavelength 405 nm and the fluorescence emission spectrum is observed using a fiber optic spectrometer. The emission wavelength depends on the sizes of the dots, the wavelength is directly proportional to the size (radius) of the nanoparticle. The demonstration is a beautiful, lucid example of the effect of size on the quantization of energy levels and brings home the idea of the potential well quite neatly.
Here is a Presentation on fluorescence from CdSe quantum dots shown in class on 18 April 2013.