Abstract

The synthetic mechanism of uniformly dispersed Cu-nanocluster doped (0.05–1.0 wt%) silica glasses (copper ruby glasses) was investigated by UV–VIS and FTIR spectroscopy, DSC, XRD, surface area and density measurements at different stages of drying/densification up to glass formation. The monolithic gels were prepared from Cu(NO₃)₂, H₂N(CH₂)₂NH(CH₂)₃Si(OCH₃)₃ (DAMO) and acid hydrolysed Si(OC₂H₅)₄ (TEOS). DAMO was used to immobilize the Cu²⁺ ions in the silica matrix. The formation and decomposition of Cu–DAMO complexes in the silica gel monoliths were studied. The doped gels were densified under H₂ and He gas atmospheres. A maximum matrix (SiO₂) density of 1.70–1.73 g cm⁻³ (77–79% of the theoretical density) could be achieved in an H₂ atmosphere at 900 °C. However a density close to silica glass 2.17 g cm⁻³ (>98.5% of theoretical) was achieved when the gels were densified in H₂ up to 800 °C followed by He gas at 980 °C. The surface area data also confirmed this densification behaviour. Uniformly dispersed Cu metal nanoclusters were formed during the heat-treatment of the gels and as a result a surface plasmon (SP) band of Cu-nanoclusters (563–580 nm) was observed. The increase of heat-treatment temperature caused the growth of nanoclusters and as a consequence the SP band was blue-shifted. XRD data also confirmed this.