Phosphorimeter

J. R. Alcala, C. Yu, and G. J. Yeh Digital phosphorimeter with frequency domain signal processing application to real time fiber optic oxygen sensing, Rev. Sci. Instrum. 64, 1554-1560 (1993). 

Once the efficiency of normal fluorescence had been determined, the efficiencies of phosphorescence and delayed fluorescence under the same conditions were derived without reference to any other solution. The ratio of the efficiencies of delayed fluorescence (6) to that of normal fluorescence was simply caculated by comparing the intensities at one of the principal maxima in the spectra, which were, of course, identical in shape. Due correction was made for the phosphorimeter factor (assumed to be 3 for lifetimes greater than 1 msec.) and also for the different instrumental sensitivities at which the two spectra were measured. Phosphorescence efficiencies were determined in a similar manner, except that the spectra first had to be corrected and the areas under the corrected curves compared with those of the corresponding normal fluorescence spectra. The phosphorimeter and instrumental sensitivity factors were then applied as before. 

Typical normal and delayed emission spectra from 5 X 10anthracene in ethanol are shown in Figure 17.38 Similar results were obtained in cyclohexane. The observed intensity of the delayed fluorescence band was about 0.28% of that of the normal fluorescence band and thus, applying the phosphorimeter factor of 3, the efficiency (6) of delayed fluorescence in this solution was approximately 0.8% of the efficiency (f) of normal fluorescence. In solutions with lower concentrations of anthracene the value of 6 was proportionately lower (see Table IV). 

H NMR spectra were recorded on a Bruker AC 400 spectrometer with tetramethylsilane (TMS) as internal reference. Infrared spectra were obtained as KBr pellets on a Perkin-Elmer 580 B FT-IR spectrometer. Electrospray (ES) mass spectra were recorded on an LCQ Finnigan Mat spectrometer. The excitation and emission spectra were obtained on a SPEX FL-2T2 spectrofluorimeter with slit at 0.8 mm and equipped with a 450 W lamp as the excitation source. Luminescence lifetimes were measured with a SPEX 1934D phosphorimeter using a 7 W xenon lamp as the excitation source with the pulse width at 3 ps. Powder X-ray diffraction patterns were recorded on Rigaku D/Max-IIB diffractometer using Cu-Ka radiation. 

The data of Figures 1 and 2 were obtained in this laboratory by Gregory Haggquist using a locally constructed phosphorimeter described in reference 6. 

A second new component is needed because phosphorescence mcasurcmcnis are usually performed at liquid nitrogen temperature in a rigid medium lu minimize collisional deactivation of the long-lived triplet state. Usually, a Dewar fla.sk with quartz windows, as shown in Figure I. i-I3. is a pan of a phosphorimeter. At the temperature u.sed. the analyte exists as a solute in a glass or solid solvent. A common solvent for this purpose is a mixture of diethylelher. pentane, and ethanol. 

Phosphorimeters. The design of a phosphorimeter is the same as that of the fluorometer, except for the use of a rotating can and Dewar flask. The sample solution is transferred into a small round quartz tube and the tube placed in a special Dewar flask filled with liquid nitrogen to freeze the solution into a glass. The lower part of the flask is smaller than the upper (see Fig. 9.6) and is also made of quartz to permit transmission of the exciting radiation and the phosphorescence emission. The Dewar is placed inside the rotating can, which has two apertures, or slits. As a slit moves into line with the monochromator beam, the sample is excited but the speed of rotation is such that any fluorescence emission ceases before the slit moves into line with the emission detector, so that only phosphorescence is observed. 

This phosphorimeter has been described in an earlier publication (Pasch, N.F. Webber, S.E. Chem. Phys. 1976, 1, 361). 

The luminescence decay curves were registered on a SPEX Fluorolog F212 spectro-fluorimeter linked to a 1934 D phosphorimeter with a 150 W pulsed xenon lamp. 

Hgure 4 Schematic diagram of events occurring during one cycle of sample excitation and observation in a pulsed-source gated-detector phosphorimeter. (Reprinted with permission from Fisher RP and Winefordner JD (1972) Analytical Chemistry 44-. 950. 1972 American Chemical Society.)... 

The phosphorescence spectra and their excitation spectra and lifetimes were obtained using an Aminco 500 spectrofluorophotometer equipped with a phosphorimeter and a photon counter [3,4]. Water-ethylene glycol 1 1 mixture (H2O-EG) was used as a glassy solvent at 77 K. The CD s were usually used in concentrations near 2.0x10 mol dm-3. The inner diameters of a-, g-, and y-CD s were taken as about 5.0, 7.0, and 8.5-9.0 A, respectively. 

There is no unifying kinetic theory that permits an interpretation of these results in terms of rate constants etc. In some cases there is not enough information available to allow a detailed interpretation (i.e. the average number of triplets/chain has only been estimated to date this could be remedied by a simultaneous TT absorption and delayed fluorescence measurement, which is not possible on most low temperature phosphorimeters). 

Fluorimeters which use a continuous fight source can usually be adapted for phosphorescence work by addition of a phosphorimeter attachment, which is usually either a pair of mechanical shutters on the excitation and emission... 

Phosphorescence measurements (spectra and decays, see Fig. 15.2) can be carried out in glasses at 77 K using a spectrometer equipped with a phosphorimeter unit (and an appropriate light source which can be a pulsed xenon lamp or a laser). The phosphorescence spectra should also be corrected for the wavelength response of the system. 

Here B and B are instrumental constants relating to the geometry of the sample and the optics of the phosphorimeter. The diffusion constant can be obtained from this equation by plotting the log of the phosphorescence intensity as a function of time, as shown in Figure 13... 

---