Toward Stable Optical Emission of Molecular Quantum Emitters: Optically Pumping Isolated Zinc Phthalocyanine Molecules in an Alkane Matrix with GaN-Based LEDs

Integrating molecules into semiconductor devices offers significant potential for complex nanoscale applications, particularly in the field of integrated optics thanks to the bright and stable photon emission of single molecular quantum emitters. For this purpose, phthalocyanine (Pc) molecules stand out with high chemical and thermal stability, as well as the ability to adjust their optical properties through chemical functionalization. However, it is an ongoing challenge to improve the emission efficiency in the crystalline phase, where fluorescence quenching through excitonic coupling becomes more prominent. To address this issue, we investigate the emission characteristics of Zinc Phthalocyanine (ZnPc) thin films, grown by organic molecular beam epitaxy (OMBE) on semiconductor surfaces. Our results demonstrate the influence of film thicknesses, ranging from multilayers to submonolayers (sub-ML), and stacking arrangements on the excitonic coupling. We were able to increase the emission intensity of ZnPc molecules in the solid phase significantly by integrating them into a co-evaporated matrix consisting of the alkane tetratetracontane (TTC). This approach allows us to reduce the excitonic coupling between the Pc molecules and presents a concept for the controlled synthesis of isolated ZnPc emitters, making them scalable for their use in optoelectronic devices. As a proof of concept for a hybrid device, we demonstrated efficient excitation of the molecules with a commercial GaN-based LED in the ultraviolet (UV) spectral range.