Yb3+ to Er3+ energy transfer and rate-equations formalism in the eye safe laser material Yb:Er:Ca2Al2SiO7

Rate equations formalism is used to predict the population ratio of the Er3+ I-4(13/2) and I-4(15/2) levels involved in the 1.55 mu m laser transition in the Yb:Er:CAS laser materials. An effective Yb --> Er energy transfer, favourable to the Er3+ 1.55 mu m laser emission, is demonstrated in this laser host. Indeed, the Yb --> Er transfer and the Er --> Yb back transfer rates are calculated to be 6 x 10(-16) and 0.45 x 10(-16) cm(3) s(-1), respectively. Attempts of codoping the system with Nd3+, Eu3+ and Ce3+ have been realised in order to increase the population of the Er3+ I-4(13/2) laser emitting level. Best results are obtained with Ce3+ ion since in the sample containing 6 x 10(20) Ce3+/cm(3), the Er3+ I-4(11/2) level lifetime is divided by a factor of 3 while the Er3+ I-4(13/2) fluorescence lifetime remains unaffected. On the contrary, codoping with Nd3+ or Eu3+ ions simultaneously decreases the Er3+ I-4(11/2) and I-4(13/2) kinetics parameters. The role of the other parameters such as Yb/Er concentrations ratio is also discussed.