[tel-01092812] Quantum Cutting Processes in Rare-earth doped fluorides for Photovoltaic applications

The occurrence of a series of consecutive energy transfers can lead to the conversion of a high-energy photon into several photons with energy lower than the incident one. This mechanism, usually referred to as quantum cutting, is here investigated in order to develop luminescent solar converters able to transform the visible and UV solar photons into several photons with energy around 1µm. The rare-earth couple Pr3+-Yb3+ presents a level structure particularly suitable for the quantum cutting mechanism since, upon absorption of a visible photon by Pr3+ (donor), two resonant energy transfers can take place through neighboring Yb3+ ions (acceptors). The efficiency of the Pr3+→Yb3+ energy transfers is here investigated within the host materials KY3F10 and CaF2. The study of the energy transfers in KY3F10 reveals a high transfer rate but also, a remarkable quenching of the Yb3+ emission. On the other hand, the investigation of the Pr3+→Yb3+ energy transfers using CaF2 as host material is particularly interesting because of the formation of rare-earth aggregates. The short distance between the dopants forming the clusters favors the apparition of extremely efficient energy transfers in this material. The quantum cutting process is finally studied with the rare-earths Tb3+ and Yb3+ in CaF2. In this case, the simultaneous excitation of two Yb3+ ions takes place through a single cooperative energy transfer from Tb3+ ions. The cooperative mechanism is known to be less efficient than resonant energy transfers , nevertheless, the rare-earth clustering in CaF2 codoped Tb3+-Yb3+ gives rise to energy transfer efficiencies notably higher than that observed with other materials



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