| Postgraduate Wang Xuejun Supervisor Professor Lu TiechengSince A. Ikesue et al. first developed Nd:YAG transparent ceramics andaccomplished laser output in 1995, transparent ceramic laser materials have arousedgreat interests among the world. Many ceramic laser materials have been preparedsince then. But up to now, visible-band ceramic laser material has not been paidmuch attention. In this paper, Mn:MgAl2O4 transparent ceramics which possesspotential application in visible-band laser material were studied. As far as I know,Mn:MgAl2O4 powders and transparent ceramics has been rarely reported.Mn:MgAl2O4 powders and transparent ceramics with different dopingconcentrations were prepared. The optimal doping concentration was approximatelydetermined through XRD and Photoluminescence analyses. In addition, themechanism for fluorescence of Mn:MgAl2O4 transparent ceramics was discussed.In experiment, Mn:MgAl2O4 powders with a series of doping concentrationswere synthesized by a high-temperature calcination method using analytically pureNH4Al(SO4)2·12H2O, MgSO4·7H2O and a certain amount of MnSO4·H2O used asdopant as raw materials. Then, Mn: MgAl2O4 transparent ceramics were preparedthrough vacuum sintering(1750℃, 2h) using previously obtained powders and someof the as-prepared samples were treated by post hot isostatic pressing(HIP 1650℃,200MPa, 2h). By means of X-Ray diffraction(XRD), Scanning ElectricalMicroscopy(SEM) analysis, compositional phases of ceramics, fracture facemorphology were studied. At the same time, the transmittance in ultraviolet and visible-band and photoluminescence were investigated using UV-VIS spectrometerand fluorescence spectrometer.Prepared ceramic samples exhibit two kinds of color, green and brown. Sampleshaving doping concentrations not larger than 10% exhibit green color. The colorbecomes deeper with increasing doping concentration. When the dopingconcentration increases to 14%, its color changes into brown from green and alsobecomes deeper when doping concentration further increases. XRD analysisindicated that no impurity phase was detected for green samples. Whereas, a newphase Mg0.9Mn0.1O was detected for brown samples.It can be obtained though the observation of fracture face morphology and themeasurement of transmittance of samples with different doping concentrations thatthe transmittance in ultraviolet and visible-band is rather low due to manyinner-grain and intergranular pores as well as bubbles; their transparency was nothighly improved by post-HIP treatment; There are two relatively strong absorptionpeaks in the range of 400-500nm and when the doping concentration is higher than5at.%, weak absorption peaks at 270nm, 357nm and 382nm appear too. Theseabsorption peaks are very weak for the reason that their corresponding transitionsare spin-forbidden, resulting in small transition probabilities.The analyses of the tests of photoluminescence showed that a strong emissionpeak around 520nm, corresponding to the transition 4T1(4G)→6A1, was observed.The emission intensity showed the maximum for 10at.% Mn-doped samples. Itsintensity dropped dramatically when the doping concentration reached 14at.%. Nonew useful emission peaks in visible-band were observed for samples with dopingconcentrations higher than 14%. So, the optimal doping concentration wasapproximately determined as 10at.%. In addition, the mechanism for correspondingexcitation spectrum was given.
|
PDF Full Text Request