Luminescence Lifetime Standards

Several standard compounds are available to check the performance of the equipment for various decay ranges. Selected standards are listed in Table 7.2 a more exhaustive list can be found in Ref. [7]. 

Andrews DL (ed) (1997) Lasers in chemistry third completely revised and enlarged edition. Springer, Berlin 

Telle HH, Urena AG, Donovan RJ (2007) Laser chemistry spectroscopy, dynamics and applications. Wiley, Chichester 

Lakowicz JR (2006) Principles of fluorescence spectroscopy, 3rd edn. Springer, New York 

Paul RL, Morales AF, Accorsi G, Miller TA, Ward MD, Barigelletti F (2003) Inorg Chem Common 6 439-442 

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Morris KJ, Roach MS, Xu WY, Demas JN, DeGraff BA (2007) Luminescence lifetime standards for the nanosecond to microsecond range and oxygen quenching of ruthenium(II) complexes. Anal Chem 79 9310-9314... 

Table 7.2 Selected standards for luminescence lifetime measurement ...

Jablonski (48-49) developed a theory in 1935 in which he presented the now standard Jablonski diagram" of singlet and triplet state energy levels that is used to explain excitation and emission processes in luminescence. He also related the fluorescence lifetimes of the perpendicular and parallel polarization components of emission to the fluorophore emission lifetime and rate of rotation. In the same year, Szymanowski (50) measured apparent lifetimes for the perpendicular and parallel polarization components of fluorescein in viscous solutions with a phase fluorometer. It was shown later by Spencer and Weber (51) that phase shift methods do not give correct values for polarized lifetimes because the theory does not include the dependence on modulation frequency. 

Spectroscopic Measurements. Absorption spectra were obtained using a Perkin-Elmer Model 554 Spectrophotometer and phosphorescence spectra and mean lifetimes were obtained at 77 K using a Perkin-Elmer LS-5 Luminescence Spectrometer coupled to a 3600 data station. Phosphorescence quantum yields were obtained by the relative method using benzophenone (0p = 0.74 in ethanol glass at 77 K) as a standard (11). 

Lamellar nanohybrids composed of Ln203 layers regularly separated from each other by organic layers of intercalated benzoate molecules can be obtained by a one-pot procedure (Karmaoui et al., 2006), the benzyl alcohol route. Lanthanide isopropoxides are simply dissolved in benzyl alcohol and reacted at high temperature (250-300 °C), resulting in the isolation of nanoparticles of 50-nm mean size. Eu -doped nanohybrids have better radiance characteristics than the standard phosphor Y203 Eu while both yttrium- and gadolinium-based nanomaterials doped with Nd display intense NIR luminescence, with a Nd( F3/2) lifetime of 49 ps in the case of the yttrium nanohybrid (Sa Ferreira et al., 2006). 

Unless otherwise noted, the aerogels were interrogated using standard spectroscopic instrumentation. The sensor respraises are recorded using a number of different types of spectroscopic measurements, including absorpti(Mi spectroscopy, luminescence emission and lifetime measurements, and Raman scattering techniques. 

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