N/Si-codoped nanocrystalline diamonds as highly sensitive luminescent thermometers

Abstract

Diamonds can host a variety of luminescent point-defects, such as nitrogen-vacancies and silicon-vacancies, making them remarkably promising materials for luminescence nanothermometry. It also fulfils the desirable characteristics of low cytotoxicity and good biocompatibility, and benefits of the carbon chemistry for tuneable surface functionalization with target molecules. In this work, N/Si co-doped nanocrystalline diamonds have been synthesized via microwave plasma enhanced chemical vapor deposition using different methane flow and temperature conditions, aiming for maximum photoluminescence intensity. In-depth analysis of the luminescence characteristics of NV- and SiV- emitting point-defects with temperature, from both experiments and ab initio calculations, suggests that a thermal coupling between their states exists, which allows for ratiometric approaches to be exploited for a more sensitive luminescent thermometry. A maximum thermal relative sensitivity of 5.5 % K-1 has been achieved. This is remarkable for in vitro temperature measurements of biological tissues.