Optical properties of SiO2 opal crystals decorated with silver nanoparticles

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.