Multi-photon quantum cutting in Gd2O2S:Tm3+ to enhance the photo-response of solar cells

Conventional photoluminescence (PL) yields at most one emitted photon for each absorption event. Downconversion (or quantum cutting) materials can yield more than one photon by virtue of energy transfer processes between luminescent centers. In this work, we introduce Gd2O2S:Tm3+ as a multi-photon quantum cutter. It can convert near-infrared, visible, or ultraviolet photons into two, three, or four infrared photons of ∼1800 nm, respectively. The cross-relaxation steps between Tm3+ ions that lead to quantum cutting are identified from (time-resolved) PL as a function of the Tm3+ concentration in the crystal. A model is presented that reproduces the way in which the Tm3+ concentration affects both the relative intensities of the various emission lines and the excited state dynamics and providing insight in the quantum cutting efficiency. Finally, we discuss the potential application of Gd2O2S:Tm3+ for spectral conversion to improve the efficiency of next-generation photovoltaics. Tm3+:Gd2O2S downconverts high-energy photons to infrared photons, making it promising for extending the spectral responses of solar cells. Conventional photoluminescence produces one photon per absorption event. Now, researchers at South China University of Technology and Utrecht University in the Netherlands have experimentally shown that the downconversion material Gd2O2S:Tm3+ respectively converts near-infrared, visible, and ultraviolet photons to two, three, and four infrared photons with a wavelength of about 1800 nanometres. By evaluating emission spectra and dynamics for various Tm3+ concentrations, they determined the rates and efficiencies of the cross-relaxation processes involved in four-photon quantum cutting. Based on this analysis, the researchers discuss the practical application of this material for enhancing the spectral response of solar cells and hence boost their efficiency. They also note that the efficient downconversion of Tm3+ may be useful for bio-imaging applications.