Impacts of Ultra-Long High Temperature Annealing on Color Centers and Color Center Spin Properties of Particulate Diamonds

Micro- and nano-sized diamond particles with color centers are some of the most promising candidates for sensing and imaging applications in biological, biomedical, and industrial fields. Traditionally, irradiated diamond particles are annealed at <i>ca.</i> 900 °C for 1-2 hours. During annealing, vacancies formed during irradiation become mobile, and their diffusion results in the formation of complexes with substitutional nitrogen to yield nitrogen-vacancy (NV) centers. Recent efforts explored the use of high temperature annealing (<i>ca.</i> &gt;1,500°C) at short timescales (seconds to minutes). At these temperatures, the diffusion of nitrogen as well as vacancies can dramatically alter the constituent color centers in the diamond particles. These high temperature annealed diamond particles exhibited enhancements in magnetically induced photoluminescence modulation, enhanced optically driven ¹³C nuclear spin polarization buildup, and extended both NV(-) as well as P1 (neutral substitutional nitrogen) spin relaxation times. Here we present a continued investigation of high temperature annealing, with a focus on the use of extended (&gt;10 hours) high temperature annealing on particulate diamond. Specifically, we explore the impact of such annealing on the photoluminescence and spin properties of NV centers.