Artificial Atom Vacancies Tailor Near-infrared Ⅱ Multiplexing Upconversion Emissions In Core/Shell Lanthanide Nanoparticles

Lanthanide-doped upconversion nanoparticles（UCNPs）attract great interests in various fields including bioimaging,anticounterfeiting,and phototherapy,due to their unique features of high photostability,limited photobleaching,and large anti-Stokes shifts.However,the low quantum efficiency of UCNPs poses a severe hurdle for their wide applications.Epitaxial growth of an inert shell around the core nanoparticles is an effective approach to enhance their luminescence;its potential in tailoring multiplexing upconversion emissions has rarely been reported.Here,by developing the atomic vacancies into color selectivity actuators,an efficient strategy to achieve inert-shell modulated multiplexing upconversion is present in 1540 nm-activated Na Er F₄@Na YF₄core-shell nanoparticles.The main results are summarized as follows:First of all,multicolor upconversion fluorescence is achieved by precisely increasing the dosage of Na OH/NH₄F during the epitaxial shell growth.Based on the fluorescent spectra and time-resolved studies,the multicolor fluorescence is attributed to the difference in the rise and decay time rate of red and green emissions.But,the F^-coordination number of Y³⁺increases from 6.7 to 8.6 with the increased dosage of Na OH/NH₄F.The evolution of inert shell structure from lower coordination number and more atomic vacancies to higher coorination number and less atomic vacancies confers an increasingly higher degree of structural integrity in the shell lattice,which confines the vibrational energy loss of the atoms and meddles into the energy transfer to alter the upconversion emission profile.Thus,the shell-tailoring multiplexing upconversion emission is attributed to the F^-coordination number.Next,the tailoring process is independent on the shell thickness and the shell host.Moreover,the current multicolor fluorescence tuning behaviour is less notable than those upon 1540 irradiation,which is attributed to that of the smaller absorption coefficient of Er³⁺in 980 nm than 1540 nm.Finally,the proof-of-concept experiments of multicolor fluorescent anticonterfeiting and subcutaneously in vivo imaging reveal the potential applications of current nanoparticles on advanced anticounterfeiting and multicolor bioimaging.To conclude,the multiplexing upconversion Na Er F₄@Na YF₄ core-shell nanoparticles are tailored by fluorine atom vacancies,which accelerate energy migration from the core to shell.What’s more,the multicolor nanoparticles exhibite great potential in anticounterfeiting and bioimaging.