Wavelength sensitivity upconversion

Wavelength Sensitivity. The overall wavelength sensitivity of emission spectrometers plays a central role in determining the accuracy of the recorded data and the range of emission wavelengths that can effectively be studied by a particular apparatus. The upconversion method adds a source of wavelength dependent sensitivity that is both useful and problematic. 

On the positive side, upconversion allows efficient detection of red wavelengths (> 650 nm) where direct detection spectrometers are insensitive. For example, for our spectrometer 700 nm fluorescence is upconverted to 422 nm. This latter wavelength is in a region where our pmt and array detectors are quite sensitive. 

The integration of Nd ions to nanomaterials containing Yb allows for Nd Yb ET to conventional Yb -sensitized upconversion processes as a versatile strategy to extend the single NIR excitation bands for Yb to shorter wavelengths. 

In Scheme 7.7, the sensitizer (Sens) absorbs a photon and the singlet intersystem crosses to the triplet, which in turn sensitizes the annihilator (Ann). This is a long-lived species and interaction of two such intermediates leads to the singlet sensitizer, which emits at a shorter wavelength than that of Ann. Castellano observed that the practically obtainable yield depends on a number of factors the ISC yield, isc, the triplet energy transfer yield, tet. the TTA yield, tta> and the fluorescence quantum yield of the emitter in the upconversion environment, Two photons must be absorbed and thus the upconversion yield, 0up> is expressed by [Eq. (7.2)]... 

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