Tuning of the fluorescence wavelength of CdTe quantum dots with 2 nm resolution by size-selective photoetching

Photoetching of CdTe nanocrystals was applied to thiol-capped CdTe quantum dots (QDs) to control their fluorescence wavelength. CdTe QDs with a high quantum yield (49%) were synthesized in aqueous solution, and they were successfully photoetched in strong alkaline (pH = 13.5) conditions. When monochromatic light was used, size-selective photoetching could be conducted; the photoetching proceeded until the band gap energy of the CdTe QDs increased to the energy corresponding to the wavelength of the irradiating light. As a result, a good linear relationship was obtained between the wavelength of the irradiating light and that of the fluorescence peak. The resulting CdTe QDs exhibited a fluorescence peak with an FWHM value as small as 23.5 nm, indicating preparation of highly monodispersed nanocrystals. The high quantum yield (ca. 45%) was maintained after the photoetching. Very fine tuning of the fluorescence wavelength with 2 nm resolution was achieved by changing the wavelength of the irradiating light by 2 nm. Theoretical calculation of the quantum size effects (effective mass approximation) predicts that a difference in the band gap fluorescence wavelength of 2 nm corresponds to a change in particle diameter of ca. 0.02 nm.