Wavelength Emission spectra

The luminescent properties of phosphor SrBP05 0.04Pr activated by Pr ion were investigated. Typical wide wavelength emission spectra of SrBPOs doped with 4mol% Pr ion, excited at 441 nm at room temperature, are shown in Figure 1. 

The broad spectral bands of the polymer may be viewed as positive with respect to the polymer accepting a wide range of light wavelengths. Emission spectra were not taken of the materials. 

So far we have examined the global cycling of carbon without paying attention to the role C02 plays in the Earth s climate. Although C02 is a minor component of the atmosphere (see Section 3.2), it plays a vital role in the Earth s radiation balance and hence in controlling the climate. This is illustrated in Fig. 7.12a, which shows the wavelength emission spectrum of the Sun and the Earth, at their effective radiating temperatures of about 5700°C and -23°C respectively. 

The numbers indicate the monitored emission wavelength (excitation spectrum) and the monitored excitation wavelength (emission spectrum) (Blasse and Dirksen, 1982). 

In an emission spectrum a fixed wavelength is used to excite the molecules, and the intensity of emitted radiation is monitored as a function of wavelength. Although a molecule has only a single excitation spectrum, it has two emission spectra, one for fluorescence and one for phosphorescence. The corresponding emission spectra for the hypothetical system in Figure 10.43 are shown in Figure 10.44. 

Continuous sources The sources of choice for measurements in the ultraviolet spectral region are hydrogen or deuterium lamps [1]. When the gas pressure is 30 to 60 X10 Pa they yield a continuous emission spectrum. The maxima of their radiation emission occur at different wavelengths (Hi A = 280 nm Di 2 = 220 nm). This means that the deuterium lamp is superior for measurements in the lower UV region (Fig. 15). 

Figure 10-8. Emission spectra of a free standing film of a blend system consisting of 0.9% MEH-PPV in polystyrene with ca. I011 cm 3 TiOj-particlcs. The nanoparlicles act as optical scattering centers. The emission spectrum is depicted for two different excitation pulse energies. Optical excitation was accomplished with laser pulses of duration I Ons and wavelength 532 nm (according to Ref. 171).

The addition of a secondary solute or wavelength shifter can serve to offset much if not all of the action of tagged nitrocompds in reducing counting efficiency. For expl nitrocompds, a shift of the emission spectrum considerably into the visible region where absorption effects are not so pronounced is clearly indicated. The secondary solute POPOP has been found to be most efficient for this purpose (Ref 2). This enhanced effect on the scintillation process is illustrated in Fig 2 for p-Nitrotoluene... 

Figure 1. Average corrected emission spectrum (- -) and excitation spectrum (- -) for quinine sulfate In 0.1 mol/L HC10 obtained during round-robin test with ten laboratories coefficient of variation at each wavelength (-t).

Figures 3a-f show the emission and excitation spectra for all six humic fractions. The excitation and emission maxima are listed in Table III along with the maxima of the phase-resolved emission spectra. In each case the emission spectrum was scanned with the excitation maximum wavelength held constant, and the excitation spectrum was scanned with the emission maximum wavelength held constant. Several interesting features are noted. The two humic samples ( Figures 3a,b) each have two excitation maxima and it appears that a double peak has been merged into the emission scan as evidenced by the shoulder on the high energy side of the emission peak. Similarly it seems evident that the exaggerated shoulders in the emission spectra of all the fractions point to the inclusion of two emission peaks in each spectrum. This evidence suggests the presence of two chromophores in each humic fraction.

Consider a sample with two fluorophores, A and B, whose lifetimes (lA and XB) are each independent of emission wavelength and are different fram one another. By setting 4>D = 4>A 90°, the contribution from A is nulled out and the scanned emission spectrum represents only the contribution from B. Similarly, the spectrum for A is obtained by setting 4>D = 4>B 90°. In practice, finding the correct value of for this... 

The process for actually measuring emissive color is somewhat different and more challenging. First, we must obtain an emission spectrum by means of a spectrofluorimeter. We cam now integrate I d> to obtain the energy and then specify this in terms of x and y. There are special methods which have been developed to do so wherein seleeted wavelengths are used, depending upon the nature of the emission spectrum. We will not delve further into this method other than to state that it does exist. 

To qualify the environment into which the colorant molecule is embedded, the actual fluorescence spectrum is compared with the one under standard conditions. If the fluorescence emission spectrum is shifted to longer wavelengths (bathochromic shift), it can be concluded that the molecular enviromnent is of a more polar nature or is polarized by the excited fluorophore. Conversely, a fluorescence shift to shorter wavelengths (hypsochromic shift) indicates a transfer of the fluorophore from a polar... 

Optical emision spectra nowadays are simply measured using a fiber optic cable that directs the plasma light to a monochromator, which is coupled to a photodetector. By rotating the prism in the monochromator a wavelength scan of the emitted light can be obtained. Alternatively, an optical multichannel analyzer can be used to record (parts of) an emission spectrum simultaneously, allowing for much faster acquisition. A spectrometer resolution of about 0.1 nm is needed to identify species. 

Additional support for this disassembly mechanism was obtained by monitoring the release of the pyrene tail units by fluorescence spectroscopy. The confined proximity of the pyrene units in the dendritic molecule results in formation of excimers. The excimer fluorescence generates a broad band at a wavelength of 470 nm in the emission spectrum of dendron 31 (Fig. 5.25). Upon the release of the pyrene units from the dendritic platform, the 470 nm band disappeared from... 

Absorption and Emission Spectra. The excitation-emission spectrum of 1 (bottom half of Fig. 1) shows that the relatively narrow emission band is nearly independent of the excitation wavelength and that the excitation spectrum is not only nearly independent of the wavelength at which the emission is monitored, but is also very similar to the absorption spectrum, both being somewhat broader than the emission band. This leaves no doubt that the observed emission is due to the polysilane, and its shape, location and the mirror image relation to the absorption permit its assignment as fluorescence. 

For recording the intensity ratio at two emission wavelengths, it should possess strongly different emission spectrum but a comparable intensity to that of reporter band. 

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