Upconversion luminescence from Er3+ in nanocrystalline Y2Si2O7:Er3+ and Y2Si2O7:Yb3+,Er3+ phosphors

Nanocrystalline yttrium pyrosilicate Y2Si2O7 (YPS) doped with Er3+(YPS:Er) or Yb3+/Er3+(YPS:Yb,Er) was obtained by the reaction of nanostructured Y2O3 and colloidal SiO2. X-ray diffraction analysis confirmed the crystallization of a single phase of α-YPS at 1150 °C and β-YPS at 1250 °C. The luminescence and upconversion spectra of Yb3+/Er3+ codoped phosphors are reported. After direct excitation at 488 nm the samples emitted mostly green radiation. Excitation at 980 nm produced green and red upconversion luminescence both from Er3+ doped and Yb3+ co-doped samples. Using 804 nm wavelength the green and red upconversion luminescences were observed for Yb3+ co-doped samples while Er3+ doped samples emitted exclusively in the green region. It was found that the Er3+ upconversion luminescence is more intense in β-YPS than in α-YPS. The dependence of upconversion luminescence intensity on the excitation power allows upconversion mechanisms for the investigated samples to be proposed.