Two-photon process leads to emission at shorter wavelengths
Fluorescence upconversion particles absorb light in the near infrared (NIR) and emit light in the visible range. These particles are currently in the focus of research because of their prospective application for, e.g., in vivo optical imaging, as they allow excitation in the NIR spectral range where light absorption and scattering from biological tissues is minimized. Another possible application are dye sensitized solar cells. A standard solar cell does not absorb in the near infrared spectral range, as the energy of the NIR light is too low for injecting electrons into the conducting band of the solar cells semiconducting material. A possible option to overcome this limitation, and thus to create solar cells with a higher light conversion efficiency, are dye sensitized solar cells in which upconversion particles are used to convert the NIR light into visible light, which then has enough energy to leap the band gap of the semiconducting material.