Upconversion

Further related processes occur in inorganic materials (quantum cutting) and in quantum dots [8, 9]. 

2 Sensitizer (Triplet) — AnniWlator (singlet excited) Fluorescence (7.1) 

The annihilator should fluoresce efficiently, have a triplet energy above that of the sensitizer, but below a half of that of its own singlet, have a long triplet lifetime, and 

In a summary of the state of the art in the field, Schmidt and Castellano [12] listed the most important advances  

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Figure B2.1.4 Fluorescence upconversion spectrometer based on the use of off-axis elliptical reflectors for the collection and focusing of fluorescence. Symbols used el, c2, off-axis elliptical reflectors s, sample x, nonlinear crystal. (After Jimenez and Fleming [21].)...

The instrument response fiinction (IRF) for the fluorescence upconversion experiment, then, caimot be shorter than the intensity cross-correlation fiinction, which can be obtained usmg an mstniment like that shown in figure B2.1.4... 

An important extension to the simplest upconversion experiment at a single detection frequency M2 is the practice of measuring time-resolvedfluorescence spectra, that is, the shape of the fluorescence spectrum... 

Figure B2.1.5 Fluorescence upconversion traces obtained at two observation wavelengdis (fiill circles, 570 mn open circles, 650 mn) at room temperature with an oxazine dye, phenoxazone, in methanol solvent. Figure courtesy of Professor S Rosenthal (Vanderbilt University).

The anisotropy fiinction r t) = (/ (t) -1+ 21 t)) is detemiined by two polarized fluorescence transients / (t) and/j (t) observed parallel and perpendicular, respectively, to the plane of polarization of the excitation pulse. In tlie upconversion experiment, the two measurements are most conveniently made by rotating the plane of polarization of the excitation pulse with respect to the fixed orientation of the input plane... 

The main cost of this enlianced time resolution compared to fluorescence upconversion, however, is the aforementioned problem of time ordering of the photons that arrive from the pump and probe pulses. Wlien the probe pulse either precedes or trails the arrival of the pump pulse by a time interval that is significantly longer than the pulse duration, the action of the probe and pump pulses on the populations resident in the various resonant states is nnambiguous. When the pump and probe pulses temporally overlap in tlie sample, however, all possible time orderings of field-molecule interactions contribute to the response and complicate the interpretation. Double-sided Feymuan diagrams, which provide a pictorial view of the density matrix s time evolution under the action of the laser pulses, can be used to detenuine the various contributions to the sample response [125]. 

Gamelin DR, Gudel HU (2001) Upconversion Processes in Transition Metal and Rare Earth Metal Systems. 214 1-56 Ganachaud F, see Elaissari A (2003) 227 169-193 Garda R, see Tromas C (2002) 218 115-132 Geraldes CFGC, see Frullano L (2002) 221 25-60... 

Gamelin DR, Gudel HU (2001) Upconversion Processes in Transition Metal and Rare Earth Metal Systems. 214 1 - 56... 

Underwood, D. E., Kippeny, T. and Rosenthal, S. J. (2001) Ultrafast carrier dynamics in CdSe nanocrystals determined by femtosecond fluorescence upconversion spectroscopy. /. Phys. Chem. B, 105,436-443. 

Wenger OS, Giidel HU (2003) Influence of Crystal Field Parameters on Near-Infrared to Visible Photon Upconversion in Ti2+ andNi2+ Doped Halide Lattices 106 59-70 Wheatley AEH, see Linton DJ (2003) 105 67-139 Wilhelm M, see Haubner R (2002) 102 1-46... 

Gustavsson T, Sharonov A, Markovitsi D (2002) Thymine, thymidine and thymidine 5 -monophosphate studied by femtosecond fluorescence upconversion spectroscopy. Chem Phys Lett 351 195... 

Gustavsson T, Sarkar N, Lazzarotto E, Markovitsi D, Improta R (2006) Singlet excited-state dynamics of uracil and thymine derivatives a femtosecond fluorescence upconversion study in acetonitrile. Chem Phys Lett 429 551-557... 

Wang H, Zhang H, Abou-Zied OK et al (2003) Femtosecond fluorescence upconversion studies of excited-state proton-transfer dynamics in 2-(20-hydroxyphenyl)benzoxazole (HBO) in liquid solution and DNA. Chem Phys Lett 367 599-608... 

Kamimura M, Miyamoto D, Saito Y, Soga K, Nagasaki Y (2008) Design of polyethylene glycol)/streptavidin co-immobilized upconversion nanophosphors and their application to fluorescence biolabeling. Langmuir 24 8864-8870... 

The QD s absorption can be used directly or it can be used to get multiple exciton generation. The latter has recently been shown in suitably chosen QDs, such as PbSe and Si.36,37 This discovery allows for the potential of a variety of devices employing both upconversion and downconversion. 

Lanthanide (Ln) - or rare-earth-doped upconverting nanocrystals usually have similar optical properties as their bulk counterparts [45]. Upconversion is characterized by the successive absorption of two or more photons via intermediate... 

Soukka T, Rantanen T, Kuningas K (2008) Photon upconversion in homogeneous fluorescence-based bioanalytical assays. Ann N Y Acad Sci 1130 188-200, Fluorescence Methods and Applications Spectroscopy, Imaging, and Probes... 

Auzel F (2004) Upconversion and anti-stokes processes with f and d Ions in solids. Chem Rev 104 139-174... 

Shen, J. Zhu, Y. Chen., C. Yang, X. Li, C., Facile Preparation and Upconversion Luminescence of Graphene Quantum Dots. Chem. Common. 2011,47 2580-2582. 

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