Hi Pratap,

Simply put as the blue light is more energetic than for example green light.  The species emitting blue light must have higher energy gap between their excited and ground states as well. And as a consequence materials with higher energy excited state will tend to do all sorts of things (change geometry, break bonds, dissociate ligands, populate nonradiative triplet states at room temperature etc.) not associated with light emission, which leads to decrease of their quantum efficiency and lifetime.

I guess, it is contributed to internal non-radiative losses like carriers' recombination and delocalization and of course wide band gap too!

Hi Kaspars,

Thank you for your answer! I fully agree with you that blue light is associated with high energy as compared to other colors. However, the excited state molecular activity you have mentioned is more pronounce in solution phase fluorescence and it might not happen in OLED system as it is based on the recombination process of electron and hole. 

Thank you Sankeerthana for your response.

Hi Pratap,

indeed these reactions etc. are more commonly explored in the solution because its so much easier to do so than in the solid state, non the less even though hole-electron recombination is the general mechanism for light production in OLEDs it is also true that the spectra and QY generally is based on the emitter properties in the solution (with many exceptions of course but they are rather the abnormality not the norm), thus the excited state of which is present in the solution should be generally responsible for the emission in the solid state also. And thus most of the considerations mentioned previously also applies. This might change if rigid matices are used to ensure geometrical constants etc. But the loss of the device lifetime and QY still should be considered from this perspective.