Comprehensive research about the cooperative up-conversion luminescence of the ytterbium- doped oxyfluoride vitroceramics

Abstract

The cooperative up-conversion blue luminescence of Yb3+ ion-doped oxyfluoride vitroceramic material (Yb:FOV) and the influence of co-doped Ho3+ ion, when excited by a 960 nm diode-laser, are studied in this paper. A strong blue 479.1 nm up-conversion luminescence of the Yb:FOV material is discovered. It is found that the 479.1 nm luminescence results from the cooperative up-conversion of the coupled states of the Yb3+–Yb3+ clusters formed by two adjacent Yb3+ ions. The measured cooperative up-conversion luminescence main peak 479.1 nm of this paper is different from the characteristic fluorescence main peak of the Tb3+ ion positioned at about 495–504 nm wave-range. Our result coincides with all the published correct papers, whose cooperative up-conversion luminescence main peaks of the direct Yb3+–Yb3+ clusters are all positioned at about 476–480 nm wave-range. All of these indicate that the large cooperative up-conversion blue luminescence of the direct Yb3+–Yb3+ clusters discovered in this paper is stable. It further proves that the cooperative up-conversion green luminescence may result from the Yb3+-Tb3+ cooperative effect. In particular, the original work of this paper improves considerably on the traditional concept by the experimental facts that the blue 479.1 nm cooperative up-conversion luminescence strength of Yb(5):FOV is 230 times greater than that of fluoride glass Yb(3):ZBLAN. This is a great development to meet the practical requirements for blue up-conversion luminescence strength. This result indicates that the large cooperative up-conversion blue luminescence could be achieved excellently by using a suitable material, such as oxyfluoride vitroceramic, which provides a better chance to form better Yb3+–Yb3+ clusters and has less relaxation to keep the more efficient up-conversion luminescence. It is also found that impurities seriously reduce the cooperative up-conversion luminescence intensity due to the cross-relaxation from the Yb3+–Yb3+ clusters, which means that the cooperative up-conversion blue luminescence could be further improved by pure Yb3+ ion-doped materials that have as few impurities as possible to reduce the cross-relaxation. The large cooperative up-conversion blue luminescence of Yb(5):FOV also comes from its higher concentration (5 mol%) of activator Yb3+ ion which acts well because the cooperative up-conversion blue luminescence intensity varies linearly against the square of the concentration of Yb3+ ions in the range of 0.5–5 mol%. In summary, the great improvement of our work on cooperative up-conversion blue luminescence results from the comprehensive enhancement of the factors of better-coupled chance of the Yb3+–Yb3+ clusters, less cross-relaxation, better concentration contribution of Yb3+ activator, non-saturation and better up-conversion luminescence efficiency.