Efficient energy transfer from Bi to Er ions in Y2O3 thin films

Abstract

Although in the last decades rare earths (REs)-containing materials have been proposed as active media in Si compatible light sources, the reached optical efficiency is still limited by the low REs excitation cross section. In this work, the introduction of Bi as an Er sensitizer in a Si-compatible yttrium oxide thin film has been proposed in order to overcome this limit. The stabilization of optically active Bi3+ ions in place of Y3+ in the two reticular sites, S6 and C2, of Y2O3 was demonstrated. Photoluminescence (PL) and photoluminescence excitation measurements have revealed the existence of two different intense emission bands in the visible range ascribed to Bi3+ in the two reticular sites. They can be selectively excited by properly changing the excitation wavelength. Moreover, the Bi3+→Er3+ energy transfer processes in the (Bi+Er)-codoped samples were demonstrated for both Bi3+ sites by the spectral overlap between the Bi emission bands and Er excitation peaks. We estimated an Er emission enhancement by a factor of about 80 for the C2 site and 16 for the S6 site with respect to the Er direct excitation. By the recorded reduction of the Bi PL intensities and the shortening of the related lifetimes in presence of Er ions, the energy transfer efficiencies were evaluated to be about 70% for the Bi (C2) and 35% for the Bi (S6). These interesting findings suggest (Bi+Er)-codoped yttrium oxide as an efficient Si-compatible material for photonic applications.