Yb3+ effect on the spectroscopic properties of Er–Yb codoped SnO2 thin films

We have investigated the optical properties of sol–gel thin films of tin dioxide (SnO2) codoped with Er3+–Yb3+ as a function of Yb3+ concentration. The Judd–Ofelt model has been applied to absorption intensities of Er3+ (4f11) transitions to establish the so-called Judd–Ofelt intensity parameters: Ω2, Ω4, Ω6. Various spectroscopic parameters were obtained to evaluate their dependence and the potential of the samples as a laser material in the eye-safe laser wavelength (1.53 μm) as a function of Yb3+ concentration. An amelioration of the quality factor Ω4/Ω6 was found with Yb content. Both the IR photoluminescence (PL) intensity and the up-conversion emission, from Er3+ ion in SnO2, were found to increase with Yb concentration. We show that the Yb3+ ion acts as sensitizer for Er3+ ion and contributes largely to the improvement of the spectroscopic properties of SnO2:Er. The mechanism of up-conversion emission is discussed and a model is proposed. The results showed that sol–gel SnO2 is promising gain media for developing the solid-state 1.5 μm optical amplifiers and tunable up-conversion lasers.