Preparation And Study On Luminescence Properties Of Ho₂O₃ And Nd₂O₃ Doped Yttria Stabilized Zirconia Single Crystals

Yttria stabilized zirconia（YSZ）is considered as an ideal matrix because of its high melting point,high refractive index and low optical loss.Based on the unique energy level structure of rare earth elements,rare earth doped yttria stabilized zirconia single crystals showed excellent luminescence properties which is widely used in many high-tech fields,including luminescence,optical amplifier,optical storage and solid-state lasers.However,defects,matrix and rare-earth doped elements have certain effects on the luminescence properties of crystals.High quality of Ho₂O₃ doped YSZ（Ho:YSZ）and Nd₂O₃ and Ho₂O₃co-doped YSZ（Nd/Ho:YSZ）single crystals were grown by optical floating zone method.The crystals structure was characterized by using XRD and Raman spectroscopy.Mocro-defects were analyzed by positron annihilation lifetime spectra.And optical properties of the crystals were characterized by UV-visible spectrophotometer and photoluminescence spectrometer.The influence of defects and rare earth(Ho³⁺,Nd³⁺)on the luminescence properties of the crystal was discussed.The following meaningful experimental results were obtained:High quality Ho:YSZ and Nd/Ho:YSZ single crystals prepared by optical floating zone method were all in tetragonal phase.The defect concentration in Ho:YSZ crystal increased with the increasing of Y₂O₃ concentration,which reduced the quantum yield and luminescence intensity of the crystal.The optical band gap value of Ho:YSZ crystal from the absorption spectrum can be calculated to be 4.86 e V,indicating that the crystal was a wide-band gap material.The excitation spectra of Ho:YSZ crystals were measured by monitoring at 551 nm,and the excitation peak at 446 nm was the strongest.The emission spectrum of Ho:YSZ crystals was obtained with excitation light at 446 nm.The emission spectrum showed three emission peaks at green light,red light and near infrared,and the intensity of the emission peak increased first and then decreased with the increase of the concentration of Ho₂O₃.Concentration quenching occurred when the doping concentration of Ho₂O₃ was greater than 0.50 mol%,which is due to the existence of electric dipole-electric dipole interaction between adjacent Ho³⁺.CIE1931 calculated that the color coordinates of Ho:YSZ crystal were located in the green light region and the color purity of the sample is>99%,so the crystal may become a laser crystal emitting green light.Absorption spectra of Nd/Ho:YSZ crystals showed that the absorption peaks at about 250 nm correspond to the electron transitions from O 2p to Zr 4d,while the other absorption peaks correspond to the electron transition between different energy levels of rare earth ions(Nd³⁺,Ho³⁺).The optical band gap of Nd/Ho:YSZ crystal was 4.70 e V,which was smaller than that of Ho:YSZ crystal.Under the excitation light of 446 nm,the Nd/Ho:YSZ crystal also showed three emission peaks of green,red and near infrared.The addition of Nd³⁺reduced the intensity of Ho³⁺emission peak.With the increasing concentration of Nd³⁺,the non-radiative transition from ⁵F₄ to ⁵S₂ was promoted.Green emission peak can be observed in upconversion PL spectrum of Nd/Ho:YSZ crystal excited by 808 nm laser,that is,Nd³⁺can achieve upconversion luminescence,indicating that Nd³⁺could be used as Ho³⁺sensitizer to achieve upconversion green emission in YSZ matrix.Nd/Ho:YSZ crystal may be used as an upconversion green laser at 808 nm excitation.The power curve of Nd/Ho:YSZ crystal showed that the up-conversion green light emission process is a two-photon process.