CdTe quantum dots (QDs), capped with mercaptopropionic acid (MPA), were synthesized and the variation of their fluorescence properties (steady state and lifetime) with pH was assessed in solution and when immobilized in a sol-gel host. Three different sizes of CdTe QDs with excited state lifetimes ranging from 42 to 48 ns and with emission maximum at 540 nm (QD(540)), 580 nm (QD(580)) and 625 nm (QD(625)) were selected. The solution pH affects the maximum emission wavelength (shifts to higher wavelengths of 23, 24 and 27 nm for QD(540), QD(580) and QD(625), respectively), the excited state lifetime and the fluorescence intensity in a reversible way. Linearization of the maximum emission wavelength variation with the pH allows the estimation of an apparent ionization constant (pK(a)) for each QD: 6.5+/-0.1 (QD(540)), 6.1+/-0.5 (QD(580)) and 5.4+/-0.3 (QD(625)). The variation of the QDs fluorescence properties was further explored using confocal laser scanning microscopy allowing the implementation of a new calibration method for pH imaging in solution. QDs were successfully immobilized on the tip of an optical fiber by dip-coating using sol-gel procedure. The immobilized QDs showed a similar pH behaviour to the one observed in solution and an apparent lifetime of 80, 68 and 99 ns, respectively. The proposed QDs based methodology can be successfully used to monitor pH using wavelength encoded data in imaging and fiber optic sensing applications.

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Glutathione capped CdTe quantum dots (QD) were synthesised using a simple experimental procedure and two samples were subjected of study (QD550 and QD600). The maximum of the excitation and emission spectra and the emission full width of half maximum of these two QD were: QD550, 307, 550 and 37 nm; QD600, 307, 600 and 39 nm. The steady state fluorescence properties of the two QD undergo variation when the pH of the aqueous solution is varied and are characterised by different apparent pKa: QD550, 5.2+/-0.1; QD600, 6.3+/-0.3. The fluorescence intensity of the QD550 is markedly quenched by the presence of micromolar quantities of Pb(II) ion (Stern-Volmer constant of about 7x10(5) M(-1)). PARAFAC analysis of the excitation emission matrices (EEM) of QD550 acquired as function of the Pb(II) ion showed that only one linearly independent component describes the quenching of the QD550 by the Pb(II) ion allowing robust estimation of the excitation and emission spectra and of the quenching profiles.

In this work, the spectroscopic properties of Perylene were studied in different solvents, applying the Lippert equation. It has been observed that polar solvents have a more significant effect on the optical properties of Perylene.

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