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(NO(3))(2), H(2)N(CH(2))(2)NH(CH(2))(3)Si(OCH(3))(3) (DAMO) and acid hydrolysed Si(OC(2) H(5))(4) (TEOS). DAMO was used to immobilize the Cu(2+) 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 H(2) and He gas atmospheres. A maximum matrix (SiO(2)) density of 1.70-1.73 g cm(-3) (77-79% of the theoretical density) could be achieved in an H(2) atmosphere at 900 degreesC. However a density close to silica glass 2.17 g cm(-3) (>98.5% of theoretical) was achieved when the gels were densified in H(2) up to 800 degreesC followed by He gas at 980 degreesC. 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