This proposal seeks to demonstrate and understand a new class of materials for up-converting infrared (IR) radiation into the visible range through linear radiation-matter interactions, exploiting the optical and electronic properties of trivalent rare-earth ions and organic-based light harvesting compounds.It is known that materials doped with lanthanide ions are capable of combining low energy excitations into higher states via excited state absorptions and energy transfer, resulting in visible or UV emission upon IR excitation. However, the primary absorptions are partially forbidden, which results in a low performance or the requirement of relatively high exciting power. Our aim is to exploit the fact that organic chromophores can have very high absorption coefficients, several orders of magnitude greater than the lanthanide ions, and can act as primary sensitizers by transferring the excitation to them, thus providing an effective increase in absorption and hence, in up-conversion. Following recent discoveries on the nature of the organics to be employed towards this end, we will pursue a twofold strategy. On one hand we will study up-converting organolanthanide polymers incorporating IR chromophores and on the other hand, hybrids based on well known, efficient lanthanide-doped inorganics in combination with IR absorbing organic dyes. The inclusion of chromophore-containing dyes will be done though chemical methods during the synthesis or via coating of nanostructures to exploit inter-molecular and inter-domain energy transfer. We will aim at design rules through opto-structural correlations derived by spectroscopic and characterization experiments at ambient and high pressure of the un-sensitized and sensitized materials.The study and approach are expected to impact on the multidisciplinary Material Science community due to the applications in optical and solar cell technologies as well as Biology due to potential uses in labeling and therapy.