Upconversion Emission in Tm/Er/Yb Co-Doped Yttria Stabilized Zirconia Single Crystals

Blue, green, and red emissions through upconversion and energy transfer processes are investigated as a function of the Tm 3+ concentration in Tm/Er/Yb triply doped yttria stabilized zirconia (YSZ) crystals upon excitation at 980 nm. YSZ doped with 0.075–0.250 mol% Tm 2 O 3 , 1.50 mol% Er 2 O 3 , and 2.00 mol% Yb 2 O 3 are prepared by the optical floating zone method, and confirmed to be in the cubic phase by X-ray diffraction. The blue emission corresponds to the Tm 3+ 1 G 4 → 3 H 6 transition, and is produced through a three-photon process, whereas the green and red light are emitted through two-photon processes from the Er 3+ 2 H 11/2 → 4 I 15/2 and 4 S 3/2 → 4 I 15/2 transitions for green and the Er 3+ 4 F 9/2 →4I 15/2 transition for red. However, interactions between the different lanthanide ions is a factor in determining the overall color of these triply doped crystals, and this is not simply a summation of the results from the singly doped systems, so this mechanism of energy transfer is discussed in detail. The CIE color chromaticity coordinates for the present samples under excitation at 980 nm approach (0.39, 0.55), which is in the yellow-green region.