Rare earth ions and Ge nanocrystals in SiO(2)

Experimental studies of Ge nanocrystals embedded in SiO(2) films doped with Er and Yb deposited by rf-magnetron sputtering are presented. Although inter-band photoluminescence (PL) from the Ge nanocrystals is not observed, it is nevertheless found that the presence of Ge nanocrystals is crucial for obtaining light emission from Er(3+) and Yb(3+). For both kinds of rare earth ions, the intensity of the related PL line has a maximum after heat treatment at 800 °C, and the PL excitation spectra for the two cases are very similar. This suggests that the presence and the structure of the nanocrystals are important for the efficiency of PL from Er(3+) and Yb(3+). Experiments performed with multilayer structures of Ge nanocrystals and SiO(2) show that the optically active rare earth ions are located in the SiO(2) layers, and not inside the Ge nanocrystals. The mechanism of energy transfer from Ge nanocrystals to the rare earth ions is found to be non-optical.