Bi_(12)SiO_(20)∶Mn,Cr晶体的杂质诱导光色特性

Impurity Induced Photochromic Behavior in Bi_(12)SiO_(20):Mn,Cr crystals

采用提拉法、电阻炉加热铂坩埚,a 轴取向生长纯的 Bi_(12)SiO_(20)和 Bi_(12)SiO_(20)∶0.05wt·%MnO_2,0.02wt·%Cr_2O_3(BSO∶Mn,Cr)晶体。电子顺磁共振谱指出:光照后激活心电荷态各自为 Mn^(5+)和 Cr^(4+);其 g 因子大小分别为2.0009和1.9616。光照前 BSO∶Mn 在410～750nm 有吸收带,并和吸收边重叠,它相应于 Mn^(5+)离子 ~3A_2→~3T_2,~3T_1跃迁,Mn^(5+)和 Mn^(4+)同时在晶体里存在。光照后,Mn^(5+)离子吸收增加。另外,BSO∶Cr 光色效应可通过 Cr^(5+)→Cr^(4+)电荷传输过程来解释。纯 BSO 晶体粉末有一个 g=2.0109峰宽为75G 的 ESR 带,这带被归为本征捕获空穴心。

The pure Bi_(12)SiO_(20) and Bi_(12)SiO_(20);O.05wt%MnO_2,0.02wt%Cr_2O_3(BSO;Mn,Cr)crystals Were grown along the A-axis by the Czochralski technique using resi-stance heated platinum crucibles.Electron spin resonance spectra indicate that accep-table Charge states of the centers after illumination are Mn^(5?) and Cr^(4+),and the g-factors of centers are 2.0009 and 1.9616,respectively.Observed BSO:Mn beforeillumination has the absorptionband between 410～750nm which overlaps the absorp-tion edge due to ~3A_2—~2T_2,~3T_1 transition of Mn^(5+) ions;and Mn^(5+) and Mn^(4+)aresimultaneously present in the crystal.Absorption due to Mn^(5+) will increase afterillumination.The photochromic effect of BSO:Cr is explained in terms of a Cr^(5+)—Cr^(4+) charge transfer process.A ESR band appears at g=2.0109 with peak widthof 75 G at RT in pure BSO crystal powder,and this band is attributed to an in-triusic trapped hole center.