Pressure modified upconversion luminescence of Yb3+ and Er3+-doped Bi3TeBO9 ceramics

Abstract

Yb3+ and Er3+-doped Bi3TeBO9 ceramics exhibit efficient upconversion luminescence in the visible spectral range upon laser diode excitation at 975 nm. Bi3TeBO9:Yb3+/Er3+ powder was prepared by means of the modified Pechini method. A series of Bi3TeBO9:Yb3+/Er3+ ceramic samples was fabricated using the high-pressure low-temperature technique, by sintering Bi3TeBO9:Yb3+/Er3+ powder under different pressures (2, 4, 6 or 8 GPa). The structure and morphology of the above-mentioned samples were analyzed using XRD, SEM and EDX measurements. The phonon energy of Bi3TeBO9 matrix associated with the vibrations of TeO6 and BO3 molecular groups was revealed using μ-Raman spectroscopy. The low phonon energy of Bi3TeBO9 matrix allows the effective energy transfer between Yb3+ and Er3+ ions as well as the 2H11/2 → 4I15/2, 4S3/2 → 4I15/2 and 4F9/2 → 4I15/2 transitions from the excited to ground states of Er3+ ions, resulting in efficient upconversion emission at 523, 540 and 653 nm, respectively. The decay times determined for all analyzed emissions were longer for Bi3TeBO9:Yb3+/Er3+ ceramics than for the powder sample. The highest values of decay times were detected for the ceramics obtained under a pressure of 8 GPa and were equal to 174, 172 and 175 μs for the emissions at 523, 540 and 653 nm, respectively. The obtained results suggest that Bi3TeBO9:Yb3+/Er3+ ceramics can be proposed as efficient spectral converters in the new type solar cells enhancing the efficiency of the photovoltaic effect.