A STUDY ON SENSITIZATION OF INFRARED EMISSION FROM Yb AND Er CO-DOPED NANOCRYSTALLINE Si THIN FILMS

本文研究了Er^<3+>离子4f壳层内跃迁对1.54 μm光致发光的敏化作用。采用激光烧蚀法在Si衬底上制备了Yb掺杂纳米晶Si（nc-Si：Yb）、Er掺杂纳米晶Si（nc-Si：Er）以及Yb和Er共掺杂纳米晶Si（nc-Si：YbEr）薄膜。在Ar激光线（488 nm）的主激发下测量了这些样品的光致发光。在nc-Si：Yb薄膜中观察到了0.980 μm的尖发射（Yb^<3+>离子的^2F_<5/2>到^2F_<7/2>跃迁）。在nc-Si：Er薄膜中检测到了0.984 μm（Er^<3+>离子的^4I_<11/2>到^4I_<15/2>跃迁）和1.535 μm（Er^<3+>离子的^4I_<13/2>到^4I_<15/2>跃迁）的发射。结果表明，Yb^<3+>和Er^<3+>离子在nc-Si薄膜中通过光生载流子的能量转移过程被激发，其中^4F_<5/2>能级比^4I_<13/2>能级高出约5 meV.因此，在nc-Si：YbEr薄膜中，由于Yb^3+离子的敏化作用，作为^2F_<5/2> → ^4I_<11/2> → ^4I_<13/2>2 → ^4I_<15/2>跃迁级联退激过程的最后一步，Er相关的1.54 μm发射被增强。实际上，在nc-Si：YbEr薄膜中观察到约3倍的与Er相关的1.54 μm发射强度的敏化。详细的I调查系统的Yb掺杂水平是需要的最佳敏化。

A sensitization of photoluminescence at 1.54 μm originating from the intra-4f shell transition in Er^<3+> ions has been investigated in this research. Yb doped nanocrystalline Si (nc-Si:Yb), Er doped nanocrystalline Si (nc-Si:Er), and Yb and Er co-doped nanocrystalline Si (nc-Si:YbEr) thin films have been fabricated on Si substrate using laser ablation. The photoluminescence from these samples, was measured under the host excitation of Ar laser line (488 nm). Sharp emission at 0.980 μm (^2F_<5/2> to ^2F_<7/2> transition in Yb^<3+> ions) was observed in nc-Si:Yb thin films. The 0.984 μm emission (^4I_<11/2> to ^4I_<15/2> transition in Er^<3+> ions) and 1.535 μm emission (^4I_<13/2> to ^4I_<15/2> transition in Er^<3+> ions) were detected in nc-Si:Er thin films. This result indicates that the Yb^<3+> ions and Er^<3+> ions are excited through an energy transfer process due to the photo-induced carriers in the host nc-Si thin films, and the ^4F_<5/2> level is in located higher energy side by about 5 meV than ^4I_<13/2> level. Therefore, it is expected in nc-Si:YbEr thin films that Er-related 1.54 μm emission as the last step of cascaded de-excitation process of the ^2F_<5/2> → ^4I_<11/2> → ^4I_<13/2>2 → ^4I_<15/2> transitions is enhanced due to playing as the sensitizer of the Yb^<3+> ions introduced. Indeed, about 3 times sensitization on the Er-related 1.54 μm emission intensity was observed in nc-Si:YbEr thin films. Details of the I investigation on the systematical Yb doping level are required for the optimum sensitization.