Upconversion-Enabled In Situ Growth of Silver Nanostructures Mediated by Cavity Resonance in Single Microrod

Solution-based photochemical reaction is widely utilized in the syntheses of metallic nanocrystals. Although seedless photochemical reaction can avoid pre-treatments, it relies on long, high-energy radiation. Here, this work demonstrates an upconversion-enabled seedless photochemical approach to synthesize grating-like silver nanostructures on a hexagonal NaYF4 microrod via a near-infrared laser excitation. Experimental results show that upconversion emission enables the nucleation and growth of Ag nanoparticles. Meanwhile, the emission can be also precisely tuned and enhanced by in situ growth of silver nanoparticles on the NaYF4 and NaYF4@SiO2 microrods. The maximum enhancement factor of 2 in overall emissions is achieved for the NaYF4@SiO2 microrod. This fabrication approach and results visually confirm the cavity resonance of excitation light inside the microrod via the distribution of Ag nanostructures. Moreover, the in situ grown Ag nanostructures provide a tunable far-field upconversion emission via the plasmonic effect, which is potentially useful for tunable microlasers, biosensing, antibacterial, and catalytic applications.