One of a wide-bandgap semiconductor, Zinc oxide (ZnO) has a near ultraviolet bandgap (3.37 eV) and an exciton binding energy of 60 meV at room temperature (RT), and has several favorable properties, such as high electron mobility, high oscillator strength, and good transparency. In the photoluminescence (PL) spectra of ZnO nanoparticles, the near band edge ultraviolet (UV) emission at 378 nm relevant to direct bandgap of ZnO, and blue light emissions centered at 410, 435, and 465 nm corresponding to Zn interstitial (Zni) to valence band maximum (VBM), and to Zn vacancies (VZn) and green light emission at 540 nm corresponding to conduction band maximum (CBM) to oxygen vacancy (Vo). Ultra-small size quasi consolidated ZnO-graphene nanoparticles was synthesized in which graphene outer layer was chemically attached with ZnO inner core. After attaching graphene to ZnO, green emission completely disappeared whereas the intensity of blue emission was greatly increased. Enhanced blue emission could be well described by both fast electron transfer from CBM of ZnO to graphene having similar molecular energy level with Zni and transition to VBM and Vzn. Glass/ITO/PEDOT:PSS/poly-TPD/ZnO-graphene/Cs2CO3/Al were fabricated and showed the blue emission centered at 435 nm with FWHM of about 90 nm.
Won Kook Choi, Hong Hee Kim, Cheolmin Park, Do Kyung Hwang, and Yeonju Lee, "Blue light emission from ZnO-graphene hybrid quantum dot (Conference Presentation)," Proc. SPIE 10105, Oxide-based Materials and Devices VIII, 101050S (Presented at SPIE OPTO: January 31, 2017; Published: 19 April 2017); https://doi.org/10.1117/12.2253809.5393342244001.
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Study of self-shadowing effect as a simple means to realize nanostructured thin films and layers with special attentions to birefringent obliquely deposited thin films and photo-luminescent porous silicon