Triplet–triplet annihilation based near infrared to visible molecular photon upconversion

Triplet–triplet annihilation based molecular photon upconversion (TTA-UC) is an exciting research area

for a broad range of photonic applications due to its tunable spectral range and possible operation at

non-coherent solar irradiance. Most of the TTA-UC studies are limited to Visible to Visible (Vis to Vis)

energy upconversion. However, for several practical photonic applications, efficient near infrared (NIR)

to Vis upconversion is preferred. Examples include, (i) photovoltaics where TTA-UC could lead to

utilization of a larger part of the solar spectrum and (ii) in NIR stimulated biological applications where

the deep penetration and non-invasive nature of NIR light coupled to TTA-UC offers new opportunities.

Although, NIR to Vis TTA-UC is known since 2007, the recent five years have witnessed quite a progress

in terms of the development of new chromophores, hybrid systems and fabrication techniques to

increase the UC quantum yield at low excitation intensity. With this tutorial review we are reviewing

recent progress, identifying existing challenges and discus possible future directions and opportunities.