Energy-transfer upconversion

Upconversion lanthanide-containing nanophosphors, which emit higher-energy photons when excited by lower-energy photons have stirred increasing research interest in recent years. The predominant mechanisms of upconversion in nanophosphors are excited-state absorption (ESA), energy-transfer upconversion (ETU) and photon avalanche (PA) (Prasad, 2004 Auzel, 2005). In the ESA process, two photons are sequentially absorbed by the same ion,... 

Schematic illustration of UC processes for ions (a) excited state absorption (ESA) upconversion, (b) energy transfer upconversion (ETU), (c) photon avalanche (PA) upconversion, and (d) energy migration-mediated upconversion. The dotted, dashed-dotted, and full arrows represent energy transfer, nonradiative relaxation, and photon absorption/emission processes, respectively.

Upconversion mechanism (a) ground state absorption followed by excited state absorption (GSA/ESA) (b) ground state absorption followed by energy transfer upconversion (GSA/ ETU) (c) Cross relaxation (CR). 

Tsuboi T, Murayama H. Energy-transfer upconversion of rare earth ions in ionic crystals case of Tm /Ho -codoped LiYF4 crystals. J AUoys Compd 2006 408-412 680. 

Fig. 9 Some upconversion processes SHG second harmonic generation, TP A two-photon absorption, GSAj ESA ground state absorption/ excited state absorption, PA photon avalanche, ETU energy transfer upconversion. Refer to the text for explanation...

Two-Photon Absorption, Ground State/Excited State Absorption, and Energy Transfer Upconversion... 

The simplest energy transfer upconversion (ETU) involves a cross-relaxation process between two ions. The processes ESA and ETU can be distinguished by energy dependence measurements, such as by recording the excitation spectrum of the luminescent state. For example, the mechanism of upconversion luminescence of Tm " in TmP50i4 was investigated by Chen et al. [128]. Pumping the p2 multiplet (15,153 cm ) by a 659 nm laser was observed to lead the luminescence D2 p4 at 450 nm. The intensity of the D2 emission, 7em, varied as ... 

Activator In energy transfer upconversion (ETU) process, an activator receives energy from the nearby excited ions and releases an emission light with a specific wavelength. 

ATPE = addition de photons par transfert d energie EDTA = ethylenediamine tetraacetic acid EG = ethylene glycol ESA = excited state absorption ETU = energy transfer upconversion GSA = ground-state absorption HRTEM = high-resolution transmission electron microscopy ... 

T1O2 sol-gel layers, 27 Er-Zr second shell coordinations, 27 ESA. See excited state absorption etching technique, 442 ETU. See energy transfer upconversion Euler s critical stress, 226 europium-activated photonic crystal, 379 europium-doped systems. See also erbium-doped systems aluminum-codoping, 378 electric dipole aspects, 373 FLN spectra, 376 luminescence spectra, 374 magnetic dipole aspects, 373 non-radiative lifetimes, 375 non-radiative transitions, 375 radiative lifetimes, 375 room temperature spectra, 376 silica gels, 376... 

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