Growth And Optical Properties Of Sm₂O₃ And Gd₂O₃-doped Yttria-stabilized Zirconia (YSZ) Single Crystals

Yttrium oxide stabilized zirconia(YSZ)crystals have excellent physical and chemical stability.Rare earth element doped YSZ single crystals exhibit excellent luminescence properties,and have uses in many high-tech fields,including luminescence,optical storage,and solid-state lasers.In this work,the optical floating-zone method was used to prepare rare earth doped YSZ single crystals with a range of Gd₂O₃ contents(Gd:YSZ)and a mixture of Gd₂O₃ and Sm₂O₃(Gd/Sm:YSZ),in which the Gd₂O₃ content was varied whilst the Sm₂O₃ content was fixed at 0.75 mol%.X-ray diffraction,Raman spectroscopy and electron paramagnetic resonance were used to characterize the structure and microdefect of these crystals.Absorption and emission spectra were measured by ultraviolet-visible-near infrared spectroscopy and photoluminescence spectrometry,and were used to understand the effects of the rare earth ions on the optical properties of the crystals.The most significant results are summarized below:The Gd₂O₃:YSZ and Gd/Sm:YSZ single crystals were all in the cubic phase and of high quality with no detectable inclusions or cracks.EPR spectra of Gd₂O₃:YSZ crystals showed progressive broadening of the Gd³⁺signal with increasing Gd³⁺content,and in addition two weak radical defect signals that are interpreted as originating from an O^-ion and an unpaired electron associated with an O vacancy.The UV-Vis absorption spectra of Gd₂O₃:YSZ crystals showed four peaks at 245,273,308 and 314 nm with the maximum absorption at 273 nm.Excitation spectra of these crystals measured at 314 nm showed two peaks at 251 nm and 273 nm.The peak at 251 nm was broad and may be a combination of the Gd³⁺⁸S_7/2?⁶D_J(J=5/2,7/2,9/2)and the O^2-?Zr⁴⁺charge transfer transitions,whilst the stronger peak at 273 nm corresponds to the Gd³⁺⁸S_7/2?⁶I_J(J=7/2,9/2,11/2,13/2,15/2,17/2)transitions.On excitation at273 nm,the emission spectra of Gd₂O₃:YSZ crystals showed peaks at 308 nm and 314 nm,which correspond to the Gd³⁺⁶P_5/2?⁸S_7/2 and ⁶P_7/2?⁸S_7/2 transitions,respectively.The peak at 314 nm was the stronger,and its intensity increased with increasing Gd³⁺concentration to a maximum in the sample prepared with 2.00mol%Gd₂O₃,then decreased with higher Gd₂O₃ concentrations as a result of concentration quenching through electric dipole-dipole interactions.These results suggest that Gd₂O₃:YSZ crystals could function as lasers that emit ultraviolet light.In addition to peaks from Gd³⁺,UV-Vis-NIR spectra of Gd/Sm:YSZ crystals also showed absorption peaks that correspond to Sm³⁺transitions from the ⁶H_5/2ground state to the excited states ⁴K_15/2(345 nm),⁴D_3/2(363 nm),⁶P_7/2(377 nm),⁴F_7/2(405nm),⁶P_5/2(419 nm),⁴G_9/2(436 nm),⁴I_13/2(466 nm),⁴I_11/2(482 nm),⁴G_7/2(500 nm),⁴F_3/2(531 nm),⁴G_5/2(558,571 nm),⁶F_11/2(936 nm),⁶F_9/2(1067 nm),⁶F_7/2(1219 nm),⁶F_5/2(1352 nm),and ⁶F_3/2+⁶H_15/2+⁶F_1/2(1467 nm).The most intense Sm³⁺absorption peak was at 405 nm in the visible light range.The strongest peak in the excitation spectra of Gd/Sm:YSZ crystals measured at 314nm was at 273 nm,and its intensity decreased with increasing Gd³⁺concentration.When measurements were made at 621 nm,the strongest peak was at 404 nm.The peak strength first increased with increasing Gd³⁺concentration,reached a larger value for the sample prepared with 2.25 mol%Gd₂O₃ and 0.75 mol%Sm₂O₃,and then decreased with higher Gd³⁺concentrations.The emission spectra of Gd/Sm:YSZ crystals at 273 nm showed peaks at 571,621,654 and 716 nm corresponding to the ⁴G_5/2?⁶H_J(J=5/2,7/2,9/2,11/2)transitions of Sm³⁺,the strongest emission peak was at 621 nm.The emission intensity of red and orange light is larger,for the sample with 2.25 mol%Gd₂O₃ and 0.75 mol%Sm₂O₃,and electronic multi-level interactions were the main cause of quenching at higher concentrations.The color coordinates for the red-orange light emitted by Gd/Sm:YSZ crystals with various Gd³⁺concentrations under excitation at 273 nm,were located near(0.573,0.426).Overall,Gd/Sm:YSZ crystals have potential use as red-orange lasers.