Red-to-Blue Photon Upconversion Enabled by One Dimensional CdTe Nanorods

Photon upconversion via triplet-triplet annihilation creating light in the high energy regime of the visible spectrum could prove particularly useful in applications such as photocatalysis. Quantum-confined semiconductor nanocrystals have previously been shown to function as efficient triplet sensitizers in green-to-blue upconversion schemes, but an improvement in the apparent anti-Stokes shift of the upconversion scheme will be beneficial for future commercial applications. Additionally, both zero- and two-dimensional quantum-confined sensitizers have been investigated, but not one-dimensional nanomaterials. In this work, we fill a hole in the present field of photon upconversion by accomplishing both of these feats. Specifically, we introduce CdTe nanorods as a new class of triplet sensitizers for red-to-blue photon upconversion. When the triplet transmitter ligand (9-anthracenecarboxylic acid) and triplet annihilator (9,10-diphenylanthracene) are added to the nanorods, we observe efficient photon upconversion at a normalized upconversion efficiency of h_uc = 4.3% and a low threshold power of I_th = 93 mW/cm². The introduction of one-dimensional triplet sensitizers could yield future research that effectively harnesses the unique properties of these materials allowing for new approaches for efficient photon upconversion, especially at large apparent anti-Stokes shifts.