Preparation of uniformly dispersed copper nanocluster doped silica glasses by the sol gel process

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(OH2H5)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.