Luminescent SiO2 particles: porous structure of matrix and stability of quantum dots

Luminescent CdSe/Cd0.5Zn0.5S quantum dots (QDs) with narrow size distribution and high photoluminescence (PL) efficiency were fabricated via a two-step organic synthesis. The QDs were coated with a SiO2 shell by a reverse micelle route. The thickness of SiO2 shell on the QDs was adjusted for investigating the effect of the porous structure of SiO2 matrix on the stability of the QDs. When the shell thickness of SiO2 shells is less than 5 nm, the pores of SiO2 shell are type II (cylindrical pores). In contrast, the pores of SiO2 shell are type IV (one-neck-flask-shaped pores) while the shell thickness is 10 nm. The stability of SiO2-coated QDs was investigated in phosphate-buffered saline (PBS, pH - 7.4) buffer solutions using various phosphate concentrations. The QDs coated with a SiO2 shell with type IV pores revealed high stability compared with those with type II pores. This is ascribed that cylindrical pores (type II) accelerated the transfer of ions in SiO2 shells compared with type IV pores.