Detection limitations of photomultiplier tubes in pulsed-laser emission spectroscopy: time-resolved fluorescence spectra of chlorophyll solutions

Abstract

. 60,2198 (1982). An experimental method is described for determination of the onset of saturation effects on the performance of photomultiplier tubes (PMTs) used in time-resolved pulsed-laser spectroscopy. Changes in the dark level response in time (on the 0-100 ns time scale) of the PMT were observed to indicate saturation of the tube. At low repetition rates conditions were found for which an RCA 8850 PMT and an RCA 7 102 PMT can be used to obtain reliable fluorescence decays on the 0-100 ns time scale while operating at high anode currents, without modification of interdynode voltages.Results for time-resolved fluorescence studies of Chl n in solution, in benzene and in pyridine, are discussed. The fluorescence decays at -680 nm indicate that several Chl a species are present in each solution. In pyridine, the main fluorescence process at 677 nm, characterised by a lifetime of -7 ns, is assigned as arising from ligated monomeric species of Chl n . A second longer-lived and weaker component (r = 75 ns) is assigned to the ligated monomeric species of Chl n '. A third, and even weaker process characterised by a lifetime r = 145 ns is also observed. The time-resolved fluorescence spectral band shape ofthis component has aunique narrow profile, and is assigned to a dimeric or more highly aggregated species of Chl n . The time-resolved measurements also indicate that another emission band occurs at 740 nm, and that this process has a lifetime 75 ns < r < 145 ns.A. DE WILTON, L. V. HALEY et J. A. KoNINGSTEIN. Can. J. Chem. 60, 2198Chem. 60, (1982. On dkcrit une m6thode experimentale pour determiner le debut des effets de saturation sur la performance des tubes photomultiplicateurs (TPM) utilises dans la spectroscopie laser a impulsion, a resolution en fonction du temps. On a observe des variations dans la reponse au niveau sombre dans le temps (dans 1'Cchelle de temps allant de 0 a 100 ns) du TMP indiquant ainsi la saturation du tube. A de faibles vitesses de repetition, on a trouve les conditions dans lesquelles on peut utiliser des tubes photomultiplicateurs RCA8850 et RCA7 102 pour obtenir des valeurs sures pour la desintegration de la fluorescence a des Cchelles de temps allant de 0 a 100 ns lorsqu'on opkre avec de forts courants anodiques sans modification des voltages interdynodes.On discute des resultats obtenus lors d'etudes de fluorescence, resolue en fonction du temps, du composi Chl n en solution dans le benzkne et dans la pyridine. Les desintegrations de la fluorescence ?I 680 nm indiquent que plusieurs espkces de Chl n sont presents dans chaque solution. Dans la pyridine, on attribue le mode principal de fluorescence a 677 nm, caractirise par un temps de vie d'environ 7 ns, a des espkces monomkres de Chl n reliees entre elles. On attribue une deuxikme composante plus faible et d'une duree de vie plus longue (r = 75 ns) 5 des espkces monomkres de Chl n ' reliees entre elles. On a Cgalement observe un troisieme processus qui est encore plus faible et qui est caracterisk par un temps de vie r = 145 ns. ...

Analysis of the pulsed-laser-induced fluorescence spectrum of the chlorophyll a dimer in solution

“…A discussion of the use of photomultiplier tubes as detectors in time-resolved pulsed-laser-induced fluorescence spectroscopy has also been presented. 4 It is emphasized that these detectors have a limited dynamic range when operated in the pulsed mode; at higher light levels saturation effects may cause nonlinear response in the intensity of the signal as a function of time, leading to erroneous interpretation of fluorescence decays.…”

Polymerization evaluation by spectrophotometric measurements

“…Replacing 1 -02 -»3 -. --a; -... for ai and grouping the terms with the same a,, gives A=lc (4) Suppose now that the overall concentration increases n times, becoming c' = nc. According to the laws of equilibrium, the association increases with the concentration, but it does not mean that the concentration of each species will increase n times.…”