Synthesis and Study of Stable and Size-Controlled ZnO–SiO2 Quantum Dots: Application as a Humidity Sensor

Abstract

This study reports a synthesis by the sol–gel method of stable and size-controlled ZnO quantum dots (QDs) embedded into a SiO2 matrix in the diameter range of 2.7–5.5 nm with strong visible emission in the blue-green region. X-ray diffraction and selected area electron diffraction techniques evidence a wurtzite structure of the prepared ZnO QDs. Transmission electron microscopy investigation highlights that the ZnO nanoparticles produced in methanol solution have a nonuniform shape. Addition of tetraethyl ortho-silicate (TEOS) in the solution at different times blocks the nucleation of the QDs and allows the control of the QD size due to a SiO2 capping. Moreover, Fourier transformed infrared analysis and X-ray photoelectron spectroscopy (XPS) were used to show the ZnO QD composition and to confirm their incorporation into the SiO2 matrix by the creation of a Zn–O–Si crossing link. A strong UV band and a weak visible band are revealed at room temperature by photoluminescence (PL) measurement for pure ZnO n...