Upconverted fluorescence

The term nonlinear optical property refers to an optical property, which can be modified by exposing the material to intense light irradiation. In this section, we focus on the cascaded first- (/ 1 ) and third-order ( / ) susceptibilities describing nonlinear absorption (ESA and 2PA) and nonlinear refraction (n2) processes. Z-scan, pump-probe, and two-photon upconverted fluorescence techniques are among the most used experimental methods for determining optical nonlinearities. 

The 2PF technique measures the upconverted fluorescence induced by 2PA. This technique allows for the measurement of 2PA cross sections that are less than tens of GMs when the fluorescence quantum yield is large. The technique was first proposed by Kaiser et al. [76] in 1961 and represents an indirect way to measure the 2PA cross section, which can be calculated by comparing the integrated fluorescence signal... 

We employ method B to study effects of this type. In this mode, our apparatus yields relative high-resolution fluorescence spectra at different time windows after excitation of the sample by the 355 nm pulse. The spectra are acquired by the upconversion method. The upconverted fluorescence spectrum is recorded simultaneously at all monitored wavelengths by an optical multichannel analyzer. It is constructed from a poly-chromator (HR320 Instruments SA) and an intensified silicon photodiode array detector (Princeton Applied Research Model 1412). The detector is interfaced to our Cromemco computer. 

Photodiode Array Versus Photomultiplier Detection. The advantages of photodiode array detection, PDA, as compared to photomultiplier tube, pmt, detection for emission spectroscopy are well known (19). These advantages are especially important for the specific examples we discuss here, namely, upconverting emission spectroscopy. This is dramatically demonstrated in Figure 7 where we compare single channel pmt versus multichannel PDA detection of a small portion of the upconverted fluorescence spectrum of coumarin 520 in ethanol solvent at room temperature. 

Figure 22 (a) Upconverted fluorescence intensity proflle of a deaerated acetonitrile solution of anthracene (1.3 x 10 M) -b... 

Figure 4. TSvo >hoton upconverted fluorescence emisaon of 1 at several fs pulse pump wavelengths (a). Plot of total integrated fluorescence intensity as a fioKtion of pump power at two wavelengths (b).

Chatterjee D. K., M. K. Gnanasammandhan and Y. Zhang, Small Upconverting Fluorescent Nanoparticles for Biomedical Applications, Small, 6, 2781-2795 (2010). 

---