Colour tunability in a bimodal fluorescent hybrid nanostructure UCNPs@AuNPs@QDs

Abstract

In the present work, lysine modified NaY0.78Er0.02Yb0.2F4 upconversion nanoparticles (UCNPs, positively charged) and lysine modified ZnSe:Mn2+ quantum dots (QDs, positively charged) are attached onto the surface of citrate reduced gold nanoparticles (AuNPs, negatively charged). The gold nanoparticles not only entangle the QDs and the UCNPs, through electrostatic interaction, but also tune the optical properties of UCNPs through the effect of surface plasmon resonance. The hybrid nanostructure gives green emission both through photoluminescence (under UV excitation) and through photon upconversion (under IR light excitation) process. The colour tuning is observed through variation in the size of QDs and through plasmonic effect of gold nanoparticles. In both the cases, the colour of emission gradually changes from green to red. The colour tunability and bi-modal photon conversion property of this material could be useful for its application in the field of bio-imaging and solar energy harvesting.