Ultraviolet upconversion enhancement in triply doped NaYF4:Tm3+, Yb3+ particles: The role of Nd3+ or Gd3+ Co-doping

Deep UV upconversion emissions centered at 311 nm from the NaYF4:20mol%Yb3+,0.5mol%Tm3+,ymol%Gd3+ sample (left) and 289 nm from the NaYF4:20mol%Yb3+,0.5mol%Tm3+,xmol%Nd3+ sample (right) under 980 nm excitation resulted from the energy transfer circulation within the Yb3+,Tm3+,Gd3+ and Yb3+,Tm3+,Nd3+ systems as illustrated at the center.319