Preparation And Upconversion Luminescence Properties Of Tm₂O₃,Ho₂O₃ And Yb₂O₃ Co-doped Cubic Zirconia Single Crystals

In recent years,new artificial crystal materials have shown good development prospects in many fields by replacing traditional glass,ceramics,and powder materials.Zirconia crystal material has become an excellent host material due to its excellent physical and chemical properties.Rare earth-doped cubic zirconia upconversion luminescent materials have broad application prospects in the field of high-efficiency light-emitting,sensors,solar cells and other fields.In this paper,high-purity Zr O₂,Y₂O₃,Yb₂O₃,Ho₂O₃,Tm₂O₃ nano-powders are used as raw materials,and ceramic rods are obtained by solid-phase reaction,and two class of single crystals of yttrium oxide stabilized zirconia are prepared by optical floating zone method,one co-doped with different concentrations of Tm₂O₃ and 0.75 mol%Ho₂O₃ and 1.50 mol%Yb₂O₃（denoted as:x Tm/0.75Ho/1.50Yb:YSZ）,another co-doped with different concentrations of Yb₂O₃ and 0.75 mol%Tm₂O₃,0.0075 mol%Ho₂O₃（denoted as x Yb/0.75Tm/0.0075Ho:YSZ）.The microstructure and luminescence properties of the samples were characterized.The results are as follows:（1）The single crystals without cracks,without bubble wrapping,and crystal clear were grown by optical float zone method.The grown single crystal samples are all cubic structures at room temperature,rare earth ions are uniformly distributed in the crystal,and the incorporation of rare earth ions leads to slight changes in the unit cell volume of the samples.（2）The transmittance of x Tm/0.75Ho/1.50Yb:YSZ crystal samples in the visible region is about 80%,and the optical band gap of the YSZ crystal is about4.6 e V.Under 980 nm laser excitation,four up-conversion emission peaks in the range of 450-900 nm were monitored.The blue light emission intensity reached maximum value when the concentration of Tm₂O₃ was 0.30 mol%,and then decreased with the further increase of the concentration,which is related to the concentration quenching caused by the electric dipole-dipole interaction.The increase of Tm₂O₃ concentration reduces the nonradiative transition probability of Ho³⁺⁵F₄ level to ⁵S₂ level to a certain extent.The results show that Ho³⁺and Tm³⁺compete with each other in absorbing the energy transferred from the excited state of Yb³⁺.（3）For x Yb/0.75Tm/0.0075Ho:YSZ crystal samples,the increase of Yb₂O₃concentration have a significant effect on the upconversion luminescence intensity and luminescence color,which is mainly manifested as anomalous red emission behivor at～680 nm caused by the redistribution of electron population on the energy level,and realize multi-color tunable emission color from cyan（0.145,0.373）to（0.142,0.309）to white light（0.329,0.337）.（4）Under the excitation of a 980 nm laser with fixed pump power,the thermal quenching temperature of the 5.00 Yb/0.75Tm/0.0075Ho:YSZ crystal sample is in the range of 373-423 K,and the crystal has high thermal quenching activation energy at high temperature,which indictes that the crystal has excellent thermal stability.（5）By measuring the crystal surface temperature,the energy differences（ΔE）of the ³F_2,3 energy levels and ³H₄ energy levels of the 3.00 Yb/0.75Tm/0.0075Ho:YSZ and 5.00 Yb/0.75Tm/0.0075Ho:YSZ crystal samples is calculated to be2167 cm^-1 and 2147 cm^-1,which is very close to the theoretical value of 2046 cm^-1 obtained by emission spectroscopy,confirming the agreement between theory and experiment.Under the excitation of different power intensities,a large chromaticity shift of the emission color from green（0.33,0.51）to white（0.32,0.33）and finally to red（0.38,0.28）was achieved.Overall,the combination of multicolor tunability and photo-thermal effect shows broad application value in high-power precision instrumentation and photo-thermal medicine.