Single-step approach to sensitized luminescence through bulk-embedded organics in crystalline fluorides

Luminescent materials enable warm white LEDs, molecular tagging, enhanced optoelectronics and can improve energy harvesting. With the recent development of multi-step processes like down- and upconversion and the difficulty in sensitizing these, it is clear that optimizing all properties simultaneously is not possible within a single material class. In this work, we have utilized the layer-by-layer approach of atomic layer deposition to combine broad absorption from an aromatic molecule with the high emission yields of crystalline multi-layer lanthanide fluorides in a single-step nanocomposite process. This approach results in complete energy transfer from the organic molecule while providing inorganic fluoride-like lanthanide luminescence. Sm3+ is easily quenched by organic sensitizers, but in our case we obtain strong fluoride-like Sm3+ emission sensitized by strong UV absorption of terephthalic acid. This design allows combinations of otherwise incompatible species, both with respect to normally incompatible synthesis requirements and in controlling energy transfer and quenching routes. Aromatic molecules often afford strong and tunable absorption, desirable for lighting applications, but incorporating them in inorganic structures without luminescence quenching is challenging. Here the broad absorption from terephthalic acid is combined with inorganic fluoride-like lanthanide luminescence in a composite material.