The ultimate goal of ESQUIRE is to demonstrate the feasibility of a new approach for the study of rare events such as the neutrinoless Double Beta Decay (0νDBD). This approach is based on a new category of scintillating materials containing nano-crystals coupled to high quantum efficiency optical photon sensors. The main objective is to realize a particle detector able to reach good energy resolutions in the region of interest for the study of 0νDBD. Its main feature consists in the use of a mass-scalable technology. The sensitivity limiting factor for the next generation experiments for the study of 0νDBD will be indeed the number of nuclei under study.

Quantum Dots (QDs) are nano-crystals of a semiconducting material that can be synthesized in solid or liquid solutions using relatively low temperature and low cost techniques. They can be produced, from the same material, as to emit any specific color of light with a very narrow emission band, simply by changing the dot’s size. Among all the quantum dots, those realized with materials containing isotopes candidate to 0νDBD, such as CdSe/ZnS, are particularly interesting. This compound is one of the most interesting because ¹¹⁶Cd and ⁸²Se have a high 0νDBD Q-value and a good natural isotopic abundance, meaning a natural lower radioactive background and higher source mass for a fixed detector mass. These materials are particularly suitable for the realization of scintillation detectors as they convert most of the energy into light because of the quantum confinement. The main purpose of ESQUIRE is to demonstrate that it is possible to convert into light, and thus reveal, enough energy to achieve the required energy resolution. In addition, being quantum dots a completely novel approach, characterized
by a fast conversion process, the studies carried out in this project could pave the way for future developments of new devices in the field of radiation detectors.

The optical photon sensors selected for ESQUIRE are Silicon Drift Detectors (SDDs) because their sensitivity is much higher than that of classical devices. Moreover, their small size allows the design of a detector array.