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The exam paper answer is 500, because we need the wavelength of "maximum absorbance." But this graph shows two curves, and the absorbance curve is omitted.

But what is the difference between an emission, absorbance, and an excitation spectrum? What are they measuring? How do you interpret/read these graphs - those with multiple curves.

Came across this graph on the net, and could someone explain/clarify.


When you have an excitation spectrum and an emission spectrum, it is for fluorescence spectroscopy. To obtain these spectra, you hold either the emission wavelength or the excitation wavelength and scan the other to gather the information. The excitation spectrum shows at what wavelengths the solution uses to produce its fluorescence. The emission spectrum shows what wavelengths are given off from the solution.

For absorbency spectrum, the solution has all the wavelengths shining on the solution, and you monitor the wavelengths of interest. The absorbency shows which wavelengths are absorbed by the solution.

The excitation spectrum has the same peaks as the absorbency spectrum; although the absorbency spectrum may have more peaks.

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  • $\begingroup$ i see... so in this case id be reading the excitation spectrum to find maximum absorbance? $\endgroup$ – confused Apr 13 '14 at 2:31
  • $\begingroup$ It would be a good indication. There might be another peak in the absorbency spectrum that is greater, but you would have to have the spectrum to tell. $\endgroup$ – LDC3 Apr 13 '14 at 3:20

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