I'm working with UpConversionNanoParticles NaYF4:Yb,Tm using Octadecen as solvent and Oleic Acid as surfactant, I have read that this kind of UCNP are photostables but I dont know if the OA can suffer light exposition and break my NP.
Oleic acid under the action of light is radicalized by a double bond and can attach water and other reagents. But it is used by you for the synthesis of nanoparticles and is removed during their cleaning. Therefore, your concerns are in vain.