| In this paper,ruby(Cr:Al2O3)with 0.025?0.4 mol%Cr2O3 and Tm:YAG(Y3Al5O12)crystals with 0.1 at.%?2.Oat.%Tm2O3 were prepared by optical floating zone method and then characterized by X-ray diffraction(XRD),Raman spectroscopy,electron paramagnetic resonance(EPR)spectroscopy,positron lifetime spectrum,optical transmission and photoluminescence(PL).The main experimental results are as follows:(1)Analysis of Cr:Al2O3 crystals by XRD and single crystal X-ray diffraction showed that the crystals were of high quality without inclusions or secondary phases.In addition to the well-known signals from Cr3+ in the a-Al2O3 structure,the EPR spectra indicated the presence of very weak signals,which may correspond to paramagnetic centers associated with an oxygen vacancy,and an electron-loss oxygen center,O-.The concentration of these paramagnetic centers was at a minimum for Cr2O3 concentration of 0.15 mol%,and additional Cr3+-derived peaks were also observed with Cr2O3 concentrations?0.15 mol%.The average positron lifetime ?m decreased first reaching a minimum in the sample with 0.15 mol%Cr2O3 concentration and then increased with the further increases of Cr2O3 concentration.There were large electron density meant few electrons when ?m was at the minimum in crystals of the 0.15 mol%Cr2O3 sample.The transmission spectra showed that there two obvious absorption peaks,410 nm and 555 nm,corresponding to 4A2?4F1 and 4A2?4F2transition respectively;the absorption intensity related to oxygen vacancy(F center)was the minimum in 0.15 mol%Cr:Al2O3 sample at the wavelength of 260 nm;the average transmittance of Cr:Al2O3 was greater than 80%in visible range.The PL spectra also varied with Cr2O3 concentrations;the emission intensities of the PL spectra increased with Cr2O3 concentration for concentrations?0.15 mol%,then decreased with the further increases in Cr2O3 concentrations.Thus the maximum luminescence emission intensity corresponding to the minimum concentration of paramagnetic structural defects were observed with 0.15 mol%Cr2O3,and the presence of additional interactions involving Cr3+ ions may contribute to the partial quenching of the luminescence at higher Cr2O3 concentrations in Cr:Al2O3 crystals.(2)The XRD showed that the prepared Tm:YAG crystals substantially all formed the YAG phase.Raman spectroscopy showed that Tm:YAG crystal was consistent with the YAG single crystal,indicating that the YAG crystal structure doped with Trm3+ ions is similar with garnet-type crystal structure.The average positron lifetime of the Tm:YAG crystals decreased first and then increased with the further increases of the Tm2O3 concentration,and reached the minimum at 1.0 at.%Tm2O3 in Tm:YAG corresponding to the largest internal electron density of the crystals,which indicated the fewest defects in 1.0 at.%Tm:YAG crystals compared to the other samples.The transmission spectra showed that there were four obvious absorption peaks,358 nm,464 nm,681 nm,780 nm,corresponding to 3H6?1D2,3H6?1G4,3H6?3F2,3,3H6?3H4 transition respectively;The average transmittance of Tm:YAG was greater than 80%in visible range.The photoluminescence spectra showed that the emission wavelength is at 460 nm excited with wavelength of 357 nm,which corresponds to the 3H6?1G4 transition being consistent with the transmission spectrum.The emission intensity increased at Tm2O3 concentrations?1.0 at.%and then decreased when the Tm2O3 concentration?1.0 at.%at wavelength of 460nm in Tm:YAG crystals.The emission intensity reached the maximum at 1.Oat.%Tm2O3 concentration in Tm:YAG crystals. |
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