Synthesis and characterization of upconversion nanophosphors NaYF4:Yb3+:Er3+/NaYF4

We carried out the solvothermal synthesis of UCNPs with the core/shell structure NaYF4:Yb3+:Er3+/NaYF4 and analyzed their photoluminescent properties depending on the nanoparticle size and preparative synthesis conditions. It has been shown that intensity and lifetime of the photoluminescence of the upconversion nanophosphors depend on the intensity of laser excitation, size of the nanoparticles and presence of an inert shell. Upon the formation of an inert shell on the surface of NaYF4:Yb3+:Er3+ nanoparticles the conversion efficiency of visible and NIR radiation in different spectral regions can increase by more than an order of magnitude due to shielding of luminescent centers from nonradiative losses at surface defects.