Luminescence of tetraphenylporphyrin by an energy transfer from photoexcited ZnO nanoparticle

Photoluminescence (PL) properties of meso-tetraphenylporphine-4,4’,4”,4’’’-tetracarboxylic acid (H_2TPP(COOH)_4) bound to ZnO nanoparticle were studied. With 1.2 H_2TPP(COOH)_4 molecules per ZnO particle, the PL intensity of H_2TPP(COOH)_4 with a 325 nm excitation was increased to a 3.2-times larger value by the conjugate formation with ZnO. The excitation spectrum of PL gave an evidence of an emission of H_2TPP(COOH)_4 by an energy transfer from ZnO. An analysis based on the Forster theory gave a reasonable value of 1.8 nm for the average distance between H_2TPP(COOH)_4 and emissive surface defects on the ZnO particle.