Recent progress of energy transfer and luminescence intensity boosting mechanism in Nd3+-sensitized upconversion nanoparticles

Rare earth doped upconversion nanoparticles can be considered as the spice of research in the field of luminescence nanomaterials due to their unique optical properties such as near-infrared excitation.Enormous works have been reported about biomedical applications of 980 nm excited and Yb^3+-sensitized upconversion nanoparticles.However,980 nm excitation wavelength overlaps with the absorption band of water molecules in the biological environment,leading to overheating effect that can induce thermal damages of normal cells and tissues.Recently,Nd^3+-sensitized upconversion nanoparticles which can be excited with 808 nm has been widely investigated as alternative nanoparticles that can surmount this issue of overheating effect.Even though Nd^3+-sensitized upconversion nanoparticles can reduce the overheating effect by 20 fold as compared to Yb^3+-sensitized counterpart,there are several factors that reduce the upconversion luminescence intensity.In this review article,photon energy harvesting and transferring mechanisms in Nd^3+,Yb^3+and emitter ions co-doped upconversion nanoparticles under 808 nm excitation are briefly discussed.Factors that affect upconversion luminescence intensity and quantum yield of Nd^3+-sensitized upconversion nanoparticles are also addressed.Besides,some of the important strategies that have been recently utilized to boost upconversion luminescence intensity of Nd^3+sensitized upco nversion nanoparticles are tho roughly summarized.Lastly,the future challenges in the area and our perspectives are in sight.

Nd^(3+)-sensitized upconversion nanoparticle coated with antimony shell for bioimaging and photothermal therapy in vitro using single laser irradiation

Combining treatment and diagnosis,called theranostics,which is achieved within single nanoparticle is an ultimate goal of many studies.Herein,we developed a new nanotheranostic agent-Nd^(3+)-sensitized upconversion nanoparticles core for dual modal imaging(i.e.,upconversion luminescence imaging and magnetic resonance imaging) and antimony nanoshell for photothermal therapy(PTT).The core-shellshell upconversion nanoparticles(NaYF_(4):Yb,Er@NaYF_(4):Yb,Nd@NaGdF_(4):Nd,named as UCNP) were firstly synthesized using thermal decomposition method and then were coated by antimony shell over the surface of UCNP using simple cost and time effective new method.Furthermore,the surface of UCNP@Sb nanostructures was modified with DSPE-PEG in order to enhance the water solubility and biocompatibility.The final nanotheranostic agent,named as UCNP@Sb-PEG,exhibits very low toxicity,good biocompatibility,very good photothermal therapeutic effect,and efficient upconversion luminescence(UCL) imaging of HeLa cells under only one laser(808 nm) irradiation.The antimony shell is quenching the upconversion emission in pristine nanotheranostic agent,but interestingly,the UCL intensity of the agent recovers progressively under 808 nm laser irradiation due to light induced degradability of antimony shell.Besides,high longitudinal relaxivity(r_(1)) obtained from the experiment approves excellent potential of the nanotheranostic agent for T_(1)-weighted magnetic resonance imaging application.