Impact of H₂O–Si(OC₂H₅)₄ and H₂O–C₂H₅OH Molar Ratios in the H₂O–Si(OC₂H₅)₄–NH₃–C₂H₅OH Mixtures on Structural and Spectral Features of Synthetic Photonic Crystals Based on SiO₂

Abstract— Photonic crystals based on amorphous SiO₂ nanospheres have been obtained in four-component H₂O–Si(OC₂H₅)₄–NH₃–EtOH systems at a constant initial volume (100 mL), a constant molar ratio of NH₃:Si(OC₂H₅)₄ = 10 : 1, and varied molar ratio of H₂O–Si(OC₂H₅)₄ (x₁) and H₂O–EtOH (x₂) within the range of 30–110 and 0.4–2.8, respectively. The increase in water concentration and simultaneous decrease in the alcohol concentration in the initial mixture have resulted in the reduction of mean diameter of the SiO₂ spheres from 440 to 270 nm. The curves of the correlation curves between effective diameter of the nanospheres– and the H₂O–Si(OC₂H₅)₄ and H₂O–EtOH molar ratio have shown two regions with different slopes: for the samples obtained at low H₂O–Si(OC₂H₅)₄ and H₂O–EtOH molar ratios for these obtained at [H₂O] : [Si(OC₂H₅)₄] > 50, [H₂O] : [EtOH] > 1. Correlations between the size of the nanospheres of oligomerized SiO₂, the initial rate of the process, and the dielectric constant of the initial mixture have been found. The spectral parameters of the photonic crystals obtained on the basis of the amorphous SiO₂ spheres have been affected by the H₂O–Si(OC₂H₅)₄ and H₂O–EtOH molar ratios in the initial mixtures.