Hydrothermal synthesis of BaYF5:Yb3+/Er3+ upconversion luminescence submicrospheres by a surfactant-free aqueous solution route

Abstract BaYF 5 :Yb 3+ /Er 3+ upconversion (UC) luminescence submicrospheres have been synthesized by the hydrothermal synthesis method. The samples were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), scanning probe microscope (SPM), transmission electron microscope (TEM), laser diffraction particle analyzer (LDPA) and UC emission spectra. The as-prepared highly crystalline BaYF 5 :Yb 3+ /Er 3+ submicrospheres are of uniform size depending on different reaction temperatures and reaction times. It is found that the usage of fluoride source NaBF 4 plays the crucial key in the formation of submicrosphere. Under the 980 nm excitation, the UC emission transitions for 4 F 9/2 → 4 I 15/2 (red), 2 H 11/2 , 4 S 3/2 → 4 I 15/2 (green) in the BaYF 5 :Yb 3+ /Er 3+ submicrospheres came from two-, two-, and two-photon UC processes, respectively. Further, the effects of Yb 3+ ion concentration, size and surface of as-prepared submicrospheres, and pumping power on the UC luminescence properties of BaYF 5 :Yb 3+ /Er 3+ have also been discussed.