Abstract

Yb is an ideal sensitisor due to desirably broad and strong absorption and the possibility of energy transfer to other rare earth ions. Multistep upconversion followed by blue fluorescence is already known in Yb:Tm:glass. The process begins with absorption of a pump photon by an Yb ion and energy transfer to the Tm ³H₅ level. Relaxation to the Tm ³F₄ level is followed by Yb-Tm upconversion, where an Yb ion de-excites from the ²F_5/2 level to the ground state and causes the Tm ion to be excited to the ³F_2,3 levels. Relaxation to the ³H₄ level is followed by a second Tm-Yb upconversion process which populates the ¹G₄ level, producing blue fluorescence due to transitions to the ground state. Low Tm concentrations (<0.5%) are required to prevent the ³H₄ + ³H₆ → 2 ³F₄ cross relaxation process. With high Tm concentrations, however, other Tm-Tm interactions become possible. One such interaction is ³F₃ cross relaxation whereby one ion relaxes to the ground state and a second is excited to the ¹D₂ level, followed by UV fluorescence due to transitions to the ground state.

© 1994 IEEE