Research Projects

Sunlight contains photons of visible light along with a small extent of UVA photons, however, high energy UV photons (especially wavelength 320 nm) are scarce in sunlight owing to the ozone layer screening of high energy UVB and UVC photons. The potential applications of the high energy UV photons (entire UVA to UVC region) are numerous such as in counterfeiting, high energies demanding photochemical reactions like photocatalysis, photovoltaics, H2 generation, challenging bond activations, bacteria killings, medical applications to name just a few. Being absent within sunlight, high energy UVB and UVC light production depend on mercury lamps, excimer-based lamps, or the high energy tail of xenon arc lamps, all of them suffer from rather short lifespans well below 2000 h and electricity-to-UV conversion efficiency close to zero. In this context, an efficient, eco-friendly alternative route needs for the creation of high-energy UV photons. Interestingly, triplet-triplet annihilation (TTA) is an interesting optical concept to create high-energy photons at expense of the low-energy photons, via the diffusion between two excited triplets of annihilator molecules. In continuation of this effort numerous NIR-to-Visible based TTA works have already been conducted, however, very limited work (with poor TTA efficiency well below 20.5 percent) on vis-to-UVA and no work on vis-to-UVB/UVC has been conducted to create high energy UV light. Notably, in this proposal, the very fundamental aim is to generate high-energy UV photons covering UVA, UVB, and UVC regions at the expense of low-energy visible light (blue) using TTA. Normally, TTA enjoys low threshold power, low excitation intensity (1 mW/cm2), and high upconversion quantum yield due to the strong organic molecular absorption of the organic probe and their high quantum yield. Hence, this project will also aim to achieve the record-breaking efficiency of the upconverted UV light towards 1 sun by designing a high quantum yield and high triplet lifetime-based annihilator. Hence, our focus of this project is to achieve the low excitation power to bring down TTA from quadratic to linear regime of excitation power dependence upon employing a high triplet lifetime-based annihilator, as the threshold intensity (Ith) of excitation power is inversely proportional to the square root of the triplet lifetime of annihilator. Notably, the achievement of visible-to-UV light conversion at a linear regime of excitation power dependence will provide the technological advancements of solar cells and will provide the effective production of UV photons by irradiation of low-energy visible light (blue). In nutshell, successful achievement of high-energy UV photons will open new application opportunities like high energy consuming catalysis reactions, solvent excitation, and synthetic UV photochemistry to name just a few, which will be under the radar of our future research directions under this project.