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Nanomaterials
Published in Mohammad E. Khosroshahi, Applications of Biophotonics and Nanobiomaterials in Biomedical Engineering, 2017
Photon upconversion is a process in which absorption of two or more photons leads to the emission of light at shorter wavelength than the excitation wavelength. It is an anti-Stokes type emission. Materials which can be used for upconversion are Ln3+, Ti2+, Ni2+, Mo3+, Re4+, Os4+, and so on. Unlike QDs, upconversion nanoparticles can absorb infrared radiation, e.g., 980 nm of commercial InGaAs diode lasers, and emit photons at visible spectra, e.g., 600 nm. Since this IR wavelength has a high penetration depth in biological tissues, it thus has the potential to be used for bioimaging applications. The upconversion process is achieved through continuous excitation of valence electrons of lanthanide ions by photon absorption or energy transfer from nearby lanthanide ions. The particles are composed of a host material doped with lanthanide ions that are sensitizers (Yb+) and activators (Er3+, Tm3+ and Ho3+). The absorption and emission peaks of upconversion nanoparticles have an emission spectrum that can be tuned wide range by changing host materials and doping density.
Emissive Nanomaterials and Liquid Crystals
Published in Klaus D. Sattler, 21st Century Nanoscience – A Handbook, 2020
Marianne E. Prévôt, Julie P. Vanegas, Elda Hegmann, Torsten Hegmann, Julia Pérez-Prieto, Yann Molard
Upconversion – Anti-Stokes Photoluminescence: In principle, combinations of lanthanides, uranides, and various transition metal species embedded in solids or in the form of upconverting nanoclusters can produce anti-Stokes upconversion emissions. Photon upconversion is the sequential absorption of two or more photons by a species eventually resulting in the emission of light at shorter wavelength than the excitation wavelength. Several different mechanisms have been recognized to be involved in upconversion either alone or in combination. The three basic upconversion mechanisms are energy transfer upconversion (ETU), excited-state absorption (ESA), and energy migration-mediated upconversion as summarized in Figure 6.13 [20].
Solar Energy Conversion Concepts
Published in Juan Bisquert, The Physics of Solar Cells, 2017
Long-wavelength photons of the solar spectrum are not suitable for direct photoelectric conversion since they are transmitted through usual semiconductors, as shown in Figure 11.2. Upconversion involves the fusion of photons to significantly change the longer wavelength photons of the sunlight spectrum toward shorter wavelengths. In the scheme of photon upconversion or anti-Stokes shift, two photons of low energy are combined to produce one photon of higher energy. Upconversion is a considerable challenge as it requires the simultaneous or sequential absorption of two or more photons with lower energy than that of the emitted photon.
Shortwave infrared-absorbing squaraine dyes for all-organic optical upconversion devices
Published in Science and Technology of Advanced Materials, 2021
Karen Strassel, Wei-Hsu Hu, Sonja Osbild, Daniele Padula, Daniel Rentsch, Sergii Yakunin, Yevhen Shynkarenko, Maksym Kovalenko, Frank Nüesch, Roland Hany, Michael Bauer
A SWIR-to-visible upconversion device, also named upconversion PD [11], upconversion OLED [12] or SWIR visualization device [13], is made by integrating an SWIR PD with a visible light-emitting unit. Such devices potentially offer an alternative route to true low-cost, pixel-free SWIR imaging. The basic idea of any upconverter is that photocurrent generated in the SWIR PD layer drives the serial connected visible light-emitting unit. Upconversion devices convert low-energy SWIR photons directly into a visible image, avoiding intermediate electronics and an external display for image visualization. Note that the functionality of an upconversion device is different from the several known photon upconversion processes. Photon upconversion describes a process that converts two or more sequentially absorbed low-energy photons into a photon of higher energy.
Recent advances with optical upconverters made from all-organic and hybrid materials
Published in Science and Technology of Advanced Materials, 2019
Roland Hany, Marco Cremona, Karen Strassel
The operating mode of upconversion devices is different from the several known photon upconversion processes. Photon upconversion is described as the process that converts two or more sequentially absorbed low-energy photons into a photon of higher energy. Sensitized triplet-triplet annihilation is one such topical example of an efficient optical upconversion process that allows light to be converted into radiation of higher energy at low power excitation. Such materials are developed, i.a., to capture the infrared region of sunlight, thereby increasing the efficiency of photovoltaic cells [11–13].