Upconversion Properties of LiNbO_3 Single Crystals Co-doped with Ho and Yb

The IR-to-visible upconversion fluorescent crystals, Yb:Ho:LiNbO3, with a constant Ho3+ concentration (0.1 mol%) and different doping concentrations of Yb3+ (0.5, 1.5, 2.0, 2.5, 3.0 mol%) are synthesized by Czochralski method in air atmosphere. X-ray diffraction shows that the obtained crystal is a single phase of LiNbO3 and the rare-earth ions occupied the Li+ or Nb5+ sites instead of the interstitial sites. Under 980 nm excitation, green and red emission bands due to the Ho3+ (5S2, 5F4)/5I8 and Ho3+ 5F5/5...