Yang, Teng I.Teng I.YangHuang, Yu WenYu WenHuangBista, PrabeshPrabeshBistaCHIEN-FANG DINGChen, JesonJesonChenChiang, Cheng TienCheng TienChiangChang, Huan ChengHuan ChengChang2023-08-212023-08-212022-12-081948-7185https://scholars.lib.ntu.edu.tw/handle/123456789/634604https://www.scopus.com/inward/record.uri?eid=2-s2.0-85143436405&doi=10.1021%2facs.jpclett.2c03064&partnerID=40&md5=f254fc74713c5e5b384b04544a3cb854Fluorescent nanodiamonds contain nitrogen-vacancy (NV) centers as quantum defects. When exposed to a continuous-wave 325 nm laser or a femtosecond 344 nm laser, the particles emit red fluorescence from NV0 centers at ∼620 nm. Power dependence measurements of the emission strength revealed a predominantly linear behavior at the laser peak intensity lower than 1 GW·cm-2, contributed mainly by photoexcitation of electrons from the valence band of diamond to the NV0 centers, followed by relaxation via electron-hole recombination. In the higher power regions, however, nonresonant two-photon interband excitation of the diamond matrix dominates the photoluminescence processes. Best fits of the experimental data to semiempirical models revealed an ionization coefficient of ∼1 cm-1 for the one-photon valence-to-defect excitation and a saturation intensity of 180 ± 60 GW·cm-2 for the two-photon interband excitation. The study provides new insight into the photoionization of NV0 centers and the interband excitation properties of diamond in the UV region.enjournal article10.1021/acs.jpclett.2c03064364493712-s2.0-85143436405https://api.elsevier.com/content/abstract/scopus_id/85143436405