Luminescence multiphoton excitation

Not surprisingly, multiphoton excitation of the luminescence of lanthanide complexes has mainly been applied to Eu and Tb complexes, yielding NIR excitation of visible luminescence. Multiphoton excitation of NIR luminescent complexes has been pioneered [79] and seems a viable option, giving rise to NIR excitation of NIR luminescence, of particular interest for luminescence detection in biological media, since both the NIR excitation light and the NIR emitted light propagate well in these materials. 

The red PL band of PS can not only be excited by above bandgap photons, but also by an intense IR (1064 nm) pulse [Di6]. Such a thermostimulated luminescence is known for the case of glasses. This observation was attributed to PS having about 100 times the third-order nonlinear optical susceptibility of bulk Si, as discussed in Section 7.3. Multiphoton excitation of the red PL band by resonant pumping of the vibrational modes of surface groups like Si-O [Di4] or Si-H [Ch8] provided evidence for excitation modes that involve the porous skeleton surface. 

Here, we will give an overview on the work on NIR labels and probes based on lanthanide ions. The emphasis will be on the NIR luminescent ions (Yb , Nd ", Er ", Pr ", Ho ", Tm " ), which may be incorporated in complexes that can be excited by ultraviolet, visible or possibly NIR light. Alternatively, multiphoton excitation and lanthanide-based upconversion make possible the use of NIR... 

Studies of lanthanide complexes under such multiphoton excitation are rare [24, 76-78], and further work is necessary to identify complexes that have a suitable response towards multiphoton excitation under biological conditions. We note that multiphoton-excited luminescence, which involves the simultaneous absorption of several photons, is different from the upconversion luminescence for lanthanide-doped phosphors described earlier in this chapter, which is based on the sequential absorption of photons. 

Eliseeva S. V., G. Aubbck, F. van Mourik, A. Cannizo, B. Song, E. Deiters, A.-S. Chauvin, M. Chergui, J.-C. G. Btinzli. Multiphoton-excited Luminescent Lanthanide Bioprobes Two- and Three-photon Cross Sections of Dipicolinates Derivatives and Binuclear Helicates, J. Phys. Chem. B, 114, 2932-2937 (2010). 

Multiphoton or two-photon laser scanning microscopy is an alternative to confocal and time-resolved microscopy for bioimaging applications. The principle has been discussed in Lanthanides Luminescence Applications and concerns a two-photon excitation from the simultaneous absorption of two photons in a single quantized event. A bioprobe that normally absorbs ultraviolet light (Xex = 350 nm) can also be excited by two photons of NIR light, at 700 nm (the wavelength is twice that required for one-photon excitation). These two photons must interact simultaneously, which means in a very small lapse time. The instrumentation requires pulse lasers to provide sufficient power, as the photon density must... 

In this chapter, we review bioimaging experiments based on lanthanide luminescence, essentially restricting ourselves to the cases dealing with lanthanide complexes and singlephoton excitation since multiphoton imaging is dealt with more completely in Chapter 5 while bioimaging with UCNPs is reviewed in Chapter 7. Literature is systematically covered up to the end of 2011 while selected newer entries are introduced in Section 4.3. 

Two-photon induced luminescence (TPL) is a multiphoton process whereby absorption of two photons causes an electron to transit from ground to excited state by way of an intermediate virtual state... 

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