Insulating SiO2 Coating Using an Alkoxide Precursor and Optical Studies for Micron-Sized ZnSe:Fe Crystals

Mid Infrared (MIR) emission of ZnSe:Fe nanocrystals (NCs) or microcrystals (MCs) has drawn great attention in the scientific community. To improve the existing technology, our solution is to develop a fiber laser system that is pumped with high power pumps having diffraction limited beam quality, and tunability across a large spectral range in the 4-micron region. This involves the development of a hybrid MIR glassy medium with Fe doped ZnSe (ZnSe:Fe) NCs or MCs that can be drawn into optical fibers for usage in a fiber laser system. In order to mix NCs or MCs of ZnSe:Fe into glassy media and survive at higher temperatures in the fabrication process, a protective coating such as SiO
2
on the surfaces of NCs or MCs is needed. In this report, precursors tetraethyl orthosilicate (TEOS) and 3-mercaptopropyl triethoxysilane (MPTEOS) were studied. SiO
2
was successfully coated on the surfaces of MCs of ZnSe:Fe by using precursor MPTEOS. Transmission electron microscopy (TEM), scanning transmission electron microscopy (STEM), electron diffraction (ED), energy dispersive spectroscopy (EDS), X-ray diffraction (XRD) and photoluminescence (PL) were employed to investigate SiO
2
coating on the surfaces of ZnSe:Fe MCs. PL spectra reveal that at cryogenic conditions, the PL intensity of SiO
2
coated m-ZnSe:Fe using precursor MPTEOS decreased about 60% as compared to that of the uncoated one, while the PL intensity of SiO
2
coated m-ZnSe:Fe using precursor TEOS lowered about 96%, at wavelength 3700 nm. This is likely due to the fact that MPTEOS has a better affinity to soft metals, e.g., zinc, than TEOS. The thickness of SiO
2
layers coated on m-ZnSe:Fe is about 60–70 nm, as compared to the bare m-ZnSe:Fe in 1–4 micron size. The conditions of the hydrolysis reaction of coating with SiO
2
layers on surfaces of micron-sized ZnSe:Fe crystals using the alkoxide precursors and their PL properties are also reported in this paper.