Considering cooperative up-conversion,cross-relaxation and excited state absorption,the rate equations of eight energy levels were founded for Yb-Er co-doped Al 2O 3 materials.The functions of coefficients of cooperative up-conversion,cross-relaxation and excited state absorption varied along with the concentrations of ytterbium and erbium were built phenomenologically.The relationship among 1.53 μm photoluminescence intensity,doped concentration,and pump power were numerically simulated for Yb-Er co-doped Al 2O 3 film.The results show that there is the optimum Yb-doped concentration when Er-doped concentration and pump power are constant.The optimal Yb∶Er ratio will decrease following with increase of pump power under the fixed Er-doped concentration,and the optimal Yb∶Er ratio will also decrease following with increase of Er-doped concentration when pump power is fixed.The computed results are in good agreement with the experiment surveys.
The effects of Au thin layers on luminescence properties of Er and Yb co-doped Al2O3 films were studied. The 1.54μm emission of Er3+ excited by the energy transfer from Yb3+ is found to be strongly enhanced by placing a Au layer on top of the films. Photoluminescence excitation spectra of the 1.54μm PL of Er3+ and time transients of the 980nm emission of Yb3+ revealed that PL enhancement arises from two different mechanisms. The first one is the enhancement of local electric fields accompanied by the excitation of surface plasmons of rough Au surfaces. The other one is the enhancement of energy transfer rate from Yb3+ to Er3+ caused by the modification of the local photonic mode density at the position of the Yb–Er coupled system.