Synthesis of CdSe nanoparticles into the pores of mesoporous silica microspheres

Semiconductor materials composed of CdSe nanocrystals (NCs) were synthesized in the pores of mesoporous silica (MS) through direct reaction between Cd ions and a selenosulfate solution at low temperatures (from -10 °C to room temperature). The negatively charged MS favours a coating of the positively charged Cd composite. Thus, Cd ions were adsorbed to the Si-OH groups to form Cd-O-Si through electrostatic interaction. The sizes of the CdSe nanocrystals were mainly determined by the pore size of the MS spheres. After expanding the pore size of MS spheres, two different pore sizes were found: ∼3.2 and ∼9.7 nm. Thus, two differently sized CdSe nanocrystals were formed in the pores of MS spheres. The size of CdSe nanocrystals showed a dependence on the pore size of the MS spheres. This result is believed to involve the photoluminescence (PL) band originating from band-to-band transition or surface states. Measurements and analysis of X-ray diffraction, transmission electron microscopy, high-resolution transmission electron microscopy, energy-dispersive spectrometry, selected area electron diffraction and PL spectra showed that the CdSe nanocrystals obtained had good crystallinity and were almost perfectly inserted into the pores of the MS spheres, which created a fluorescence emission.