Enhanced Photoluminescence from Nanodiamond via Atomic Layer Deposition Surface Coating

Nitrogen-vacancy (NV) centers in diamond hold significant potential for applications in quantum information processing, magnetometry, and sensing of electric fields and temperature through optically detected magnetic resonance (ODMR) spectroscopy. Nanodiamonds (NDs) containing NV centers offer biocompatibility and photoluminescence stability, making them ideal for bioimaging and biosensing within living cells. Improving the emission intensity of NV centers is essential for enhancing sensitivity in both quantum and biological applications. In this study, we present the synthesis and photoluminescence characterization of atomic layer deposition (ALD) Al₂O₃-coated NDs, demonstrating a fivefold increase in fluorescence intensity without compromising NV center coherence times. Time-resolved photoluminescence (TRPL) measurements confirm that the observed enhancement in fluorescence is due to an increased emission rate in Al2O3-coated NDs. Additionally, ODMR measurements reveal that the T₁ and T₂ coherence lifetimes remain unaffected by the ALD process. ODMR-based temperature measurements further indicate that the ALD coating effectively reduces localized heating caused by laser excitation, allowing for the use of higher laser power in temperature sensing applications without compromising sensing performance. These results highlight the potential of ALD-coated NDs as a robust platform for high-sensitivity quantum sensing and biosensing, with improved photoluminescence properties and preserved quantum coherence.