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

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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.