Optical properties of SiO2 opal crystals decorated with silver nanoparticles

Abstract

SiO2 opal crystals decorated with silver nanoparticles (AgNPs) have been successfully fabricated. SEM analysis revealed that the SiO2 opals have an ordered region of 25–30 μm2, and AgNPs are located into the gaps between the SiO2 nanospheres. The effect of the plasmons of AgNPs on the photoluminescence of SiO2 opal crystals were investigated. Under excitation of a 325 nm laser, we observed the quenching of the intrinsic defect emission in SiO2 as the concentration of AgNPs increased. The cause of the observed photoluminescence behavior is attributed to the interaction between surface plasmon induced by AgNPs and photoluminescence centers in SiO2 opal crystals. Then, we utilized SiO2 opals crystals decorated with AgNPs as a SERS substrate. The final enhancement factor of the Raman shift was 1.64 × 107, enabling the trace detection limit for a case of malachite green to be as low as 0.05 ppm, with a relative standard deviation of less than 1.75 %. This outcome suggests the potential for direct application of the prepared substrates in ultra-fast chemical analysis.