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Colour centres based on group-IV impurities (SiV, GeV, SnV, and PbV) in diamond are intensively investigated in the context of quantum nanophotonic applications, with some of their attractive properties stemming from the inversion symmetry of their split-vacancy configuration and their high Debye-Waller factor. In addition to inheriting the inversion symmetric properties of a split-vacancy defect, the negatively charged PbV defect is also known to have a very high zero-field splitting of its ground and excited states, leading to four optical transitions which are distinguishable in a PL spectroscopy experiment [1]. The theoretically predicted neutrally charged PbV defect is expected to have an observable transition at either 2.170 eV or 2.216 eV [2] and is speculated to retain high coherence times at significantly higher temperatures than the other group-IV colour centres [3]. As part of experiment IS668, using a combination of electron emission channeling and photoluminescence spectroscopy,.we investigate the structural formation and optical activation of PbV colour centres, varying the implantation fluence and temperature as well as the annealing temperature.
In this poster, we present the initial findings for the structural formation of PbV defects for implantation at 30, 600 and 900◦C, in addition to the corresponding annealing temperature steps, as determined by the fraction of sites occupying the bond-centered site of diamond. Our emission channeling results with $^{209}$Pb (t1/2=3.25 h) indicate that the PbV defects form immediately upon implantation at room temperature, and remain stable as the annealing temperature is increased up to 900 ◦C. The reduction of the mean-squared displacement of Pb in the substitutional site corroborates the decrease of lattice disorder for higher annealing and implantation temperatures.
To complement these findings, we performed photoluminescence spectroscopy for diamond implanted with stable $^{208}$Pb at ISOLDE with fluences varied between 1e11 and 1e13 atoms/cm$^2$ and annealing temperatures of 600, 900 and 1100 ◦C. PL spectroscopy was performed separately with 457 nm and 532 nm laser excitation energy, reproducing the expected peaks at 542 nm, 552 nm and 556 nm of the negatively charged PbV colour centre. Additionally, after 1100 ◦C annealing we observed the emergence of a new peak at 575 nm with a phonon sideband structure similar to that of the 552 nm peak in the measurements performed with 457 nm excitation energy. This new peak, as well as the 542 nm and 718 nm peaks tentatively attributed to PbV, will be the subject of an element-specific radiotracer PL experiment with radioactive $^{209}$Pb which will allow to determine whether they are indeed associated with the PbV defect in diamond.
[1] Nature Communications 10, 5625 (2019)
[2] npj Quantum Materials 5 75 (2020)
[3] Nature Communications 8, 15579 (2017)
