Controlled synthesis and upconversion luminescence properties of highly uniform and monodisperse β‐NaYF4:Yb3+,Tm3+ nanocrystals

Abstract Ytterbium, thulium (Yb 3+ ,Tm 3+ ) co‐doped β‐NaYF 4 upconversion nanocrystals (U‐NCs) were synthesized by a convenient hydrothermal method using sodium citrate as a capping agent. X‐ray diffraction (XRD) analysis revealed that NCs phase structures were dependent on reaction time. Field‐emission scanning electron microscopy (FE‐SEM) and transmission electron microscopy (TEM) results showed that the morphology of U‐NCs could be controlled by adjusting the concentration of sodium citrate added in the hydrothermal reaction. Moreover, the emission spectra of the U‐NCs were investigated to evaluate upconversion efficiency. Strong luminescence intensity of the U‐NCs was observed after tuned with optimized concentration of sodium citrate. Furthermore, the U‐NCs were incubated with MCF‐7 cells at 37°C for 24 h. Under irradiation of a 980 nm laser, the upconversion blue emission of the NCs in MCF‐7 cells can be clearly observed through a confocal microscope with an upconversion imaging system and high quality upconversion luminescence images can be acquired. Thus, prepared β‐NaYF 4 :Yb 3+ ,Tm 3+ NCs provide us with highly efficient luminescent probes which can be applied for diverse bio‐applications.