Deposition of CdSe nanocrystals in highly porous SiO2 matrices – in-situ growth vs. infiltration methods

Embedding quantum dots into porous matrices is a very beneficial approach for generating hybrid nanostructures with unique properties. In this contribution we explore strategies to dope nanoporous SiO2 thin films made by atomic layer deposition and atomic etching with precise control over pore size with CdSe quantum dots. Two distinct strategies were employed for quantum dot deposition: in-situ growth of CdSe nanocrystals within the porous matrix via successive ionic layer adsorption reaction, and infiltration of pre-synthesized quantum dots. To address the impact of pore size layers with 10 nm and 30 nm average pore diameter were used as matrix. Our results show that though potentially also small pores are accessible for the in-situ approach, this strategy lacks controllability over the nanocrystal quality and size distribution. To dope layers with high quality quantum dots with well-defined size distribution and optical properties infiltration of preformed quantum dots is much more promising. It was observed that due to higher pore volume 30 nm porous silica shows higher loading after treatment than 10 nm porous silica matrix. This can be related to a better accessibility of the pores with higher pore size. The amount of infiltrated QDs can be influenced via drop casting of additional solvent on a pre-drop casted porous matrix as well as via varying the soaking time of a porous matrix in a QD solution. Luminescent QDs deposited via this strategy keep their luminescent properties upon deposition and the resulting thin films with immobilized quantum dots are suited for nitration into optoelectronic devices.