Liquid scintillator detectors are widely used in neutrino and astroparticle detection experiments. One liquid scintillation that is increasingly being used in large-scale detection experiments is linear alkylbenzene (LAB). LAB is an attractive scintillator due to its low cost, high flash point and low toxicity; making it easier to handle than previously used toxic and flammable organic solvents. LAB is commonly used together with the fluor 2,5-diphenyloxazole (PPO) which increases luminescence yield and shifts the luminescence to longer wavelengths. In this application note the effect of PPO concentration on the luminescence decay profile of the LAB/PPO system is investigated using time-resolved X-ray excited luminescence spectroscopy.