Preparation And Optical Properties Of Yb³⁺,Ho³⁺ And Sm³⁺ Doped Yttria-Stabilized Zirconia ?YSZ? Single Crystals

The excellent physical and electronic properties of yttria-stabilized zirconia(YSZ)have generated uses in optical components,solid-oxide fuel cells,gas sensors,laser substrates,and high-temperature structural materialsSingle crystals of yttria-stabilized zirconia(YSZ)doped with different contents of holmium were prepared by the optical floating zone method,and their structures and phase composition were characterized by XRD and Raman spectroscopy.These showed that the metastable tetragonal phase was stabilized by the substitutions.Transmittance of each of the Ho3+-doped YSZ single crystals was larger than 85%in the visible region.Measurements of fluorescence spectra indicated a strong emission at a wavelength of 553.5 nm,and two weak emission peaks at 671 nm and 759 nm when the crystals were excited by light with a wavelength of 448 nm.The YSZ doped with 0.75 mol%of Ho2O3 had a relatively higher fluorescence intensity and possessed high color purity(99.7%)in the green region,indicating that it can be used to produce efficient green emissionIn the development of materials with valuable luminescence properties,we have used the optical floating zone method to prepare single crystals in the cubic phase of yttria-stabilized zirconia(YSZ)doped with 0.75 mol%Ho2O3 and various concentrations of Yu2O3.The influence of Yb3+ contents was determined for absorption and photoluminescence spectra,and fluorescence decay curves at room temperature.The absorption spectra consisted of several peaks that could be assigned to various transitions involving Yb3+ and Ho3+ ions,and oscillator strength parameters ?t(t = 2,4,6)were determined using the Judd-Ofelt theory,along with the transition probability,lifetime,and branching ratio from the absorption and emission spectra of the crystal of YSZ co-doped with 0.75 mol%Ho2O3 and 1.5 mol%Yb2O3.The ?2 value of?14×10-20 cm2 indicates that the bonding around Ho3+ involves lower symmetry and higher covalency than in several other hosts,and the value of the ratio ?4/?6 of 1.93 shows that this sample is a good candidate material for high quality laser output.Up-conversion emission spectra showed that Yb3+ doping significantly increased the emission intensity of 0.75 mol%Ho2O3 doped YSZ at green(557 nm),red(670 nm)and NIR(758 nm)wavelengths when excited by a 980 nm laser,and reached a maximum for 1.5 mol%Yb2O3.The emission at 557 nm was much sharper than that reported for nanocrystals of similar composition,where the maximum intensity was observed at 540 nm.Down-conversion PL spectra showed two prominent emission peaks at 1040 nm and 1213 nm,and the fluorescence decay curves indicate that energy transfer between Yb3+ and Ho3+ influenced the lifetime of the excited state of Ho3+which varied with Yb2O3 concentration.Overall these results indicate that these Yb/Ho co-doped YSZ crystals have considerable potential for laser and luminescence applications.Single crystals of yttria-stabilized zirconia(YSZ)doped with various concentrations of Sm2O3 were synthesized by the optical floating zone method,and their structure and spectroscopic properties characterized using powder X-ray diffraction(XRD),optical absorption,and luminescence measurements.XRD showed that the cubic phase of ZrO2 was stabilized by addition of Y2O3 and a series of absorption peaks characteristic of Sm3+ was detected by UV-visible absorption spectroscopy.Three phenomenological J-O oscillator strength parameters ?t(t = 2,4,6)were calculated to evaluate the local structure and bonding in the vicinity of the Sm3+ for the 0.75 mol%Sm2O3:YSZ sample.These were in order of ?2<?4<?6 with values of ?2=5.46×10-20 cm2,?4=10.70×10-20 cm2 and ?6=12.67×10-20 cm2,and indicate a relatively high symmetry and low covalent character for the Sm-O bond at the Sm3+ sites in the YSZ matrix.Photoluminescence spectra recorded under an excitation of 404 nm showed four emission bands centered at 571 nm,621 nm,652 nm,and 716 nm corresponding to the transitions 4G5/2?6Hj(j=5/2,7/2,9/2,11/2).The transition probability,lifetime,and branching ratio obtained from the emission spectrum of the 0.75 mol%Sm2O3:YSZ crystal showed that YSZ is a potential host for Sm3+ to achieve a reddish-orange laser output,and the Sm3+-modified YSZ crystals have a possible use in reddish-orange laser and lighting devices.