Ultraviolet and White Light Emissions from Multiphoton Upconversion Transitions in Yb/Tm/Ho Codoped Cubic Zirconia Single Crystals Excited by NIR

Under excitation at 980 nm, Tm3+ may emit ultraviolet, blue, and red light, and Ho3+ may emit green light through multiphoton upconversion processes in Yb/Tm/Ho codoped materials. However, because the probability of the electron population of the higher excited state energy levels is much lower than that of the lower ones in multiphoton upconversion processes, it is difficult to observe the ultraviolet emission of Tm3+-doped single crystals under excitation at 980 nm. Here, we report that high-quality single crystals of cubic ZrO2 codoped with Tm2O3, Ho2O3, and Yb2O3 are successfully grown by the optical floating zone method, and ultraviolet emission at 308 nm was observed for the first time from multiphoton upconversion transitions in these highly transparent, low phonon energy single crystals under excitation at 980 nm. This result demonstrates the prospect of making ultraviolet solid-state lasers pumped by near-infrared light. Moreover, bright white light was emitted from the single crystal prepared with 5.00 mol % Yb2O3, 0.75 mol % Tm2O3, 0.0075 mol % Ho2O3, 2.2425 mol % Y2O3, and 92.00 mol % ZrO2 under excitation at 980 nm, and a bright solid white light source excited by a near-infrared light-emitting diode for practical use is presented.