Luminescent nanofluids based on perovskite materials and nanodiamonds

Abstract

Nanoscience and nanotechnology have emerged as transformative fields, offering unprecedented opportunities to address complex challenges in different applications, such as biomedicine. The nanomaterials used for biomedical applications have to meet several requirements to ensure their effectiveness, safety, and suitability for specific applications. These requirements include low cytotoxicity, high biocompatibility, good stability, water dispersibility and the potential for surface engineering. Luminescent nanomaterials, in particular, must exhibit adequate optical properties such as high quantum yield, low photobleaching and absorption and emission in the biological windows (BWs). The biological windows (BW-I: 650-950 nm, BW-II: 1000-1350 nm and BW-III: 1550-1870 nm) are crucial for minimizing tissue absorption and scattering, allowing for deeper tissue penetration and improved detection of the emitted light during in vivo applications. Among the various luminescent nanomaterials proposed for biomedical applications, perovskite (ABX3) quantum dots (QDs) and nanodiamonds stand out. However, the emission wavelength of perovskite QDs typically lies within the visible range, and the potential for using nitrogen-vacancy (NV-) and silicon-vacancy (SiV-) centres in nanodiamonds for temperature sensing remains unexplored. This thesis aims to develop luminescent nanofluids based on halide perovskite QDs and nanodiamonds with optimized luminescent properties for biomedical applications. Nanofluids are colloidal suspensions of nanoparticles in a base fluid, which significantly enhance the thermal, optical, or rheological properties of the fluid due to the unique characteristics of the dispersed nanoparticles. Specifically, we synthesized Pd- and Bi-doped CsPbX3 (X = Br, I) QDs using the hot-injection method at different synthesis temperatures, and N/Si-codoped nanodiamond nanofluids through a two-step method, involving the growth of nanocrystalline diamond films through microwave plasma enhanced chemical vapor deposition, followed by milling of the films to obtain water-dispersed nanodiamonds. Various characterization techniques were employed to study the structure, morphology and optical properties of the materials. Additionally, the temperature-dependent luminescence of a N/Si-codoped diamond film was investigated. A significant contribution of this thesis is the observation of emission in the BW-I region from Pd-doped samples and N/Si-codoped diamonds for luminescence nanothermometry. The findings are expected to have practical implications for future research, particularly in the development of new luminescent nanothermometers based on N/Si-codoped diamonds, and broader applications of luminescent materials in the biomedical field, thanks to their emission within the BW-I region.