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+ 4I132 levels involved in the 1.55 μm laser transition in the Yb:Er:CAS laser materials. An effective Yb → Er energy transfer, favourable to the Er3+ 1.55 μm 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 cm3 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+ 4I132 laser emitting level. Best results are obtained with Ce3+ ion since in the sample containing 6 x 1020 Ce3+/cm3, the Er3+ 4I112 level lifetime is divided by a factor of 3 while the Er3+ 4I132 fluorescence lifetime remains unaffected. On the contrary, codoping with Nd3+ or Eu3+ ions simultaneously decreases the Er3+ 4I112 and 4I132 kinetics parameters. The role of the other parameters such as Yb/Er concentrations ratios is also discussed.