High quality upconverting NaYF4:Ln (Ln = Yb, Er, Tm) crystal layers were successfully fabricated directly onto glass substrates at a relatively low temperature of 350 °C by a novel two-step flux coating method. First, mixed pastes of solute (NaF and YF3) and dopants (LnF3) were coated on glass substrates by simple bar-coating, and then flux pastes (NaNO3 or NaNO3-NaF) were coated onto the dopant-containing solute layer. After the two-step coating, raw material-coated substrates were heated at 350 or 400 °C in an electric furnace. To remove the remaining flux, the crystal layers were washed with warm water. Finally, high quality, nanotextured NaYF4:Ln crystal layers with good adhesion were directly grown onto the glass substrates. These crystal layers consisted of densely packed idiomorphic NaYF4:Ln crystals. In particular, individual NaYF4:Ln crystals were typically shaped as hexagonal prisms. The NaYF4:Ln crystal phases depended strongly on the heating conditions, i.e., temperature and time. The NaNO3 and NaNO 3-NaF fluxes were effective for the growth of high-quality idiomorphic NaYF4:Ln crystals. Additionally, the upconversion fluorescence properties of NaYF4:Ln crystal layers were controlled by changing dopant types and ratios. The NaYF4:10%Yb,1%Er, NaYF 4:50%Yb,1%Er, NaYF4:20%Yb,1%Tm and NaYbF4:1%Er crystal layers emitted green, orange, blue and red fluorescences, respectively, under 980 nm laser irradiation.
ASJC Scopus subject areas
- Materials Chemistry