Heavy metal-free visible-to-UV photon upconversion with {over|more than} 20% efficiency sensitized by a ketocoumarin derivative
{Efficient|Effective} triplet-triplet annihilation-based photon upconversion (TTA-UC) from visible to UV light {without|with out|without having|with no|devoid of|without the need of} {using|utilizing|making use of|employing|working with|applying} heavy metals {is still|continues to be} a…