Management of light emission of near-infrared dyes mediated by nanomaterials: From anti-Stokes to anti-Kasha fluorescence.

Near-infrared (NIR) dyes are compounds that absorb/emit light mostly in the ultraviolet (UV) and NIR region and being largely transparent in the visible one. Inducing fluorescence of such compounds in the visible range will facilitate their applications as NIR or UV imaging displays, energy conversion, sensitization of solar cells, optical sensors, etc. Here, the application of different nanomaterials to help visualizing anti-Kasha (S₂ emission) and hot-band absorption (HBA) assisted anti-Stokes photoluminescence (ASPL) of NIR dyes of tricarbocyanine series is demonstrated and discussed. Specifically, four types of nanomaterials are considered, i.e., carbon nano dots, semiconductor Cu_2-xS nanoparticles, metal gold nano rods, and 2D MXene nano flakes. First, an enhancement of anti-Kasha emission in the visible (blue-green region) is demonstrated, which is usually negligible for the unaffected dyes, but which increases by about one order of magnitude, together with a strong increase of the spontaneous rate of S₂ fluorescence, as a result of immobilization of the dye molecules via interaction with carbon nano dots. Second, enhancement of anti-Stokes luminescence in the red-NIR region was realized by using plasmonic nanoparticles. Plasmonic silica-coated gold nano rods (Au@SiO₂) and mesoporous silica-coated copper sulfide nanoparticles (Cu_2-xS@MSN), whose near-infrared plasmon bands overlapped with emission band of the dyes caused enhancement of the anti-Stokes emission by 17% upon interaction of the specific dye with Au@SiO₂ and up to 50% upon interaction with Cu_2-xS@MSN, respectively. Third, thermal control of HBA-assisted ASPL was realized using MXenes. MXenes with different thermal emissivity were used to influence the activation energy of electrons by effectively cooling the electron located in the hot band to different degrees. Overall, it is discussed how various nanomaterials can offer control over the photo physical properties of NIR emitters through different mechanisms.

Dr. Dimitriev is a physicist specializing in photo physics of organic dyes and conjugated polymers, also working in other related fields such as material science of organic and hybrid hetero structures, energy conversion, photoi nduced charge transfer, ecology issues as well. He obtained his Ph.D. degree in solid state physics from Donetsk State University in 1992 and currently is a Senior Scientist at V. Lashkaryov Institute of Semiconductor Physics, National Academy of Science of Ukraine. He also works as Assistant Professor at Igor Sikorsky Kyiv Polytechnic Institute. He has been a recipient of international awards obtained from Swedish Institute, Fulbright Visiting Scholar Program, German Academic Exchange Service (DAAD), and Japan Society for the Promotion of Science (JSPS). He is the author of over 100 publications and two popular science books.