Friday Materials Science Colloquia (#10)


Friday, September 29th  2023, 12 p.m., Seminar room, U5 Building – via Roberto Cozzi 55, Milano.


Lecturer: Dr. Ottavia Bettucci

Title: Organic optoelectronic devices: the use of organic molecules from emerging photovoltaics to transistors for bioelectronic applications

Abstract: Optoelectronic devices represent a rapidly evolving field at the intersection of optics and electronics, where light is harnessed to perform a myriad of functions in modern technology[1]. This seminar aims to elucidate the role of the use of organic molecules in optoelectronic devices and their crucial role in emerging photovoltaics (DSSCs, PSCs, and OPVs) as well as in bioelectronics applications such as Organic photoelectrochemical transistors (OPECTs). The use of organic molecules has emerged as a compelling contender in optoelectronic devices offering a versatile and sustainable approach to harnessing light and electricity[2]. In the field of photovoltaics, organic molecules have revolutionized energy harvesting by enabling lightweight, flexible, and cost-effective solar cells[3]. On the other hand, in the bioelectronics field, organic photo-responsive materials offer an attractive set of advantages ranging from biocompatibility flexibility and sustainability to tunable electrical and mechanical properties[4]. These advantages make organic materials valuable tools for developing a wide range of bioelectronic devices with applications in healthcare and diagnostics. My research work aims to design, synthesize, and integrate innovative light-sensitive organic materials into optoelectronic devices to enable transformative advancements in communication, healthcare, computing, and energy harvesting.

[1] Y. Zhou et al., Front. Optoelectron. 15, 51 (2022).
[2] O. Ostroverkhova, Chemical Reviews, 22, 13279-13412 (2016).
[3] Lin X. Chen, Energy Lett, 10, 2537–2539 (2019).
[4] P. Samorì et al. J. Mater. Chem. C, 11, 7982-7988, (2023)


Lecturer: Dr. Francesca Cova

Title: Defect-related phenomena in scintillating materials for high-energy radiation detection

Abstract: The detection of ionizing radiation, such as high-energy photons (X or γ), charged particles (α, β) and neutrons, is at the heart of many strategic applications in both science and technology, including high-energy/particle physics, space exploration, medical diagnostics, border security, and industrial and environmental monitoring. In all such areas, the most widely used detectors are scintillating materials that convert the energy deposited by incoming ionizing radiation into UV or visible photons, which are then turned into electrical signals by coupled photodetectors.
Scintillation light often originates from radiative transitions at intrinsic centers or dopants used as activators: therefore, a fast and efficient transport to the luminescent centers of carriers generated upon the interaction between ionizing radiation and the  scintillating material is fundamental in the scintillation process. The efficiency and speed of carrier transfer through the host matrix are affected by the presence of defects, leading to trapping levels in the forbidden energy gap, which can temporarily capture migrating charge carriers, either delaying their radiative recombination at emission centers or decreasing the overall scintillation efficiency. In addition, the prolonged exposure to ionizing radiation may cause the formation of radiation-induced defects acting as color centers and reabsorbing the emitted scintillation light. Therefore, the study of the characteristics and role of defects in the scintillation mechanism becomes essential in the science of scintillators and has seen significant progress in the recent years, extending from inorganic single crystals to glasses, ceramics, and hybrid systems like colloidal semiconductor nanocrystals, metal-organic frameworks, and polymeric nanocomposites.
In this context, I discuss an effective approach for the investigation of the role of trapping sites in scintillating materials and for the determination of the effects of long-term and high-dose ionizing radiation exposure. Specifically, the results obtained on two main targeted materials are presented, moving from rare-earth (Ce, Pr) doped silica fibers produced by sol-gel method [1,2], to CsPbBr3 perovskite nanocrystals and acrylate perovskite-based nanocomposites [3,4]. Remarkably, the in-depth analysis of the role of point defects and of their close interplay with luminescent activators in the recombination processes governing the scintillation emission is not commonly encountered in amorphous materials, such as silica, because the inhomogeneous disorder of glass leads to the broadening of electronic levels related to defects. On the other hand, lead halide perovskite nanocrystals and nanocomposites are recently emerging as a promising new class of scintillating materials; however, despite their potential, as of today, few examples tackled in depth the mechanism leading to scintillation light, as well as not much is known on the details of trapping and detrapping processes involved in their scintillation emission.

[1] F. Cova et al., Opt. Lett. 4 (43), 903 (2018)
[2] F. Cova et al., J. Phys. Chem. C 125, 11489-11498 (2021)
[3] C. Rodà et al., Adv. Funct. Mater. 31, 2104879 (2021)
[4] M. Zaffalon, F. Cova et al., Nat. Phot. 16, 860-868 (2022)