Is this in solution or solid state? In solution, you will need to do a separate measurement using a standard with a well known PLQY (e.g. quinine sulphate = 54.6%) and measure its PL spectrum under identical conditions (see this paper for an idea of a good standard to use: Pure Appl. Chem., 2011, 83, 2213 - you will probably want a red emitter). Once you have done this, integrate the area under the PL spectrum of both curves, and using the formula in the reference I've given that should tell you.

If you are in solid state, I am not sure of a way to do it other than using an integrating sphere.

you will need to do a separate measurement using a standard with a well known PLQY (e.g. quinine sulphate = 54.6%) and measure its PL spectrum under identical conditions (see this paper for an idea of a good standard to use: Pure Appl. Chem., 2011, 83, 2213 - you will probably want a red emitter). Once you have done this, integrate the area under the PL spectrum of both curves, and using the formula in the reference I've given that should tell you.

Can anybody help me to calculate PLQY percentage from PL spectra?. Available from: https://www.researchgate.net/post/Can_anybody_help_me_to_calculate_PLQY_percentage_from_PL_spectra [accessed May 5, 2015].

these attachments are quite useful for calculating QY.