Comparison of energy transfer between Terbium and Ytterbium ions in glass and glass ceramic: Application in photovoltaic

Abstract

The structural and optical properties of thin layers based on 70%SiO₂–30%HfO₂ doped with different concentration of rare earth ions (terbium and ytterbium) have been studied with a view to integrating them in a photovoltaic cell as a spectral conversion layer in order to improve its efficiency, by using down-conversion process. These thin films were synthesized by using sol gel technique and deposited on the pure silica substrate by dip-coating method. The DC layer can be placed on the front side of a solar cell and can enhance the current by converting ultraviolet (UV) photons into a large number of visible photons.

In present study two series of samples are compared, the first series corresponds to samples treated at 900 °C (glass- S) while the second series concerns samples treated at 1000 °C (glass-ceramic- SC). These series are based on 70SiO₂–30HfO₂ activated by different molar concentrations of rare earths [Tb + Yb]/[Si + Hf] = 7%, 9%, 12%, 15%, 17%, 19% and 21%.

Photoluminescence results of reference samples (without Yb³⁺) showed an emission from ⁵D₄ to ⁷F_J (J = 3, 4, 5, 6) level characteristic transitions of Tb³⁺, with a maximum peak in the green centered at 543.5 nm corresponding to the ⁵D₄→⁷F₅ transition. For the co-doped samples a clear NIR PL emission around 980 nm was detected, due to the ²F_5/2→²F_7/2 transition of Yb³⁺ ions. From luminescence decay curves of Tb³⁺ maximum emission peak (⁷F₅→⁵D₄ transition at 543.5 nm) we have identified the energy transfer efficiency. The quantum efficiency increases by increasing the total [Tb + Yb] concentration. The most significant yield was achieved with [Tb + Yb]=19%, the maximum quantum transfer efficiency obtained was 190% for glass-ceramic samples and 161% for glassy one.