Alright! So you can't calculate PLQY just from emission spectrum. What you need is a standard (usually dyes such as Rhodamine 101, Fluorescein etc.) for which PLQY is known. Your reference should be picked in such a way that it absorbs some light where your sample absorbs light too. Once you do that, you need to know the absorbance of your standard and your sample at the wavelength where you are exciting your sample. Collect the emission spectra for both your standard and sample in the same emission wavelength range under similar fluorometer operating conditions (slit widths etc.). You should adjust the concentrations of your standard and sample in such a way that absorbance values at excitation wavelength (for emission spectra) are less than 0.1. Now if you have all these numbers, then you can calculate the PLQY of your sample as:
PLQY (sample) = {PLQY(standard)*PLI(sample)*absorption(standard)*(eta)(sample)}/{PLI(standard)*absorption(sample)*(eta)(standard)}
where PLI = area under emission spectrum (can be roughly calculated using trapezoidal rule for calculating area under a curve)
eta = refractive index of solvent (can be found online)
PLQY standard values can be found in literature. For ex. PLQY for Rhodamine 101 dye in pure ethanol is nearly 1.
The other way of calculating PLQY without using a standard is by using a fluorometer equipped with integration sphere. But I am assuming you dont have that. So, the above explained procedure might be the way to go.
Please refer to Principles of Fluorescence Spectroscopy by Lackowicz to get conversant with Fluorescence fundamentals. It is an excellent book and reference for answering your question.
- Saurabh
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