Si-Doped Nanocrystalline Diamond as Highly Sensitive Luminescence Thermometer for the Physiological Temperature Range

Abstract

Si-doped nanodiamonds are emerging as highly promising materials for luminescent thermometry in the physiological temperature range (300-325 K) due to their excellent biocompatibility, chemical inertness, and optical transparency, as well as their ability to host negative charged silicon-vacancy (SiV-) centers with sharp, photostable emission within the biological transparency windows. In this work, Si-doped nanocrystalline diamond thin films were synthesized on silicon substrates via microwave plasma-enhanced chemical vapor deposition (MPECVD) under various growth pressures and methane flow conditions, aiming to obtain the practical boundary limit of the photoluminescence intensity. The temperature dependence of key photoluminescence parameters, including intensity, full width at half maximum (FWHM), and area of the zero-phonon line emission, was investigated in the physiological range (300-325 K). The experimental photoluminescence results were interpreted with the support of first-principles density functional theory calculations, linking the defect electronic structure and electron-phonon coupling to the observed optical response. By employing multiparametric analysis, combining these thermally sensitive luminescence features in a single model, a self-calibrated approach for robust thermometry was demonstrated, optimizing the thermal sensitivity of the SiV- centers-based emission of the MPECVD diamond. A maximum relative thermal sensitivity of 2.3% K-1 was achieved, highlighting the potential of Si-doped nanodiamonds for accurate and minimally invasive temperature monitoring in complex biological environments.