Electroluminescence (EL) and photoluminescence (PL) spectra are not identical: there's a small red-shift of the PL spectrum relative to the EL spectrum.
Why is this happening if both EL and PL are caused by radiative relaxation of the same excited states?
Photoluminescence (PL) spectra of the TPD∶2∶PC (left) and TPD∶poly(2)∶PC (right) films excited at 420 nm; electroluminescence (EL) spectra of the ITO/TPD∶2∶PC/Ca (solid) and ITO/TPD∶poly(2)∶PC/Ca OLEDs. All spectra are normalised. (source)