Cooperative energy transfer in Yb3+-Tb3+ codoped silica sol-gel glasses

Optical properties of Yb3+-Tb3+ codoped silica sol-gel samples have been st udied after the gel to glass transition. Different upconversion emissions h ave been observed under near infrared excitation at about 1 mum. The Tb3+ i ons are excited by means of energy transfer processes from Yb3+ ions. The t emporal evolution of the blue-green upconversion emissions coming from Tb3 ions and their dependence on the excitation intensity at about 1 mum has b een studied. The experimental results are in good agreement with a cooperat ive resonant energy transfer mechanism from Yb3+ ions. An efficient backtra nsfer process is observed from Tb3+ ions towards Yb3+ ions. The upconversio n efficiency, which is limited by this backtransfer process, has been obtai ned and compared with other upconversion results in similar matrix. (C) 200 1 American Institute of Physics.