Interband and Intraband Optical Transitions in Mercury Chalcogenide Colloidal Quantum Dots

We study the optical transitions in mercury chalcogenide colloidal quantum dots (CQDs) by using Fourier transform infrared spectrometer. The optical absorption measurements revealed distinct optical transition processes in mercury telluride (HgTe) CQDs and mercury selenium (HgSe) CQDs. The results show that the spectral absorbance of HgTe CQDs is broadband, which is originated from the interband optical transition between valence band to conduction band, while that of HgSe CQDs is narrowband. And we speculate that the narrowband absorption is resulted from the intraband transition in HgSe CQDs. Furthermore, both the interband energy gaps of HgTe CQDs and intraband energy gaps of HgSe CQDs have been estimated based on the spectral absorbance. The extracted energy gaps are in good agreement with the calculated values by two-band Kroning-Penny model.