Energy transfer between shallow centers and rare-earth ion cores: Er3+ ionin silicon

Two-color optical spectroscopy is used to directly manipulate shallow level s available in Si:Er samples of different parameters. It is observed that t he excitation energy provided by a laser operating in the visible can be te mporarily stored by trapping photogenerated carriers at shallow centers ava ilable in the material. Subsequently, this energy can be transferred to the 4f-electron: core of the Er3+ ion in a trap ionization process induced by a mid-infrared pulse from a free-electron laser. In that way, Er-related lu minescence at 1.5 mu m can be generated by an infrared pulse applied within several milliseconds after the band-to-band excitation pulse. By scanning the wavelength of the free-electron laser, ionization-spectra of the shallo w centers participating in the energy transfer are obtained, allowing for t heir identification. On that basis, the involvement of thermal donors is su ggested. The results demonstrate that excitation of Er ions in Si is a mult ichannel energy transfer;,process where shallow centers play an important r ole.