Photoluminescence excitation spectroscopy of SiV⁻and GeV⁻color center in diamond

Abstract

Color centers in diamond are important quantum emitters for a broad range of\napplications ranging from quantum sensing to quantum optics. Understanding the\ninternal energy level structure is of fundamental importance for future\napplications. We experimentally investigate the level structure of an ensemble\nof few negatively charged silicon-vacancy (SiV$^{-}$) and germanium-vacancy\n(GeV$^{-}$) centers in bulk diamond at room temperature by photoluminescence\n(PL) and excitation (PLE) spectroscopy over a broad wavelength range from 460\nnm to 650 nm and perform power-dependent saturation measurements. For SiV$^{-}$\nour experimental results confirm the presence of a higher energy transition at\n~ 2.31 eV. By comparison with detailed theoretical simulations of the imaginary\ndielectric function we interpret the transition as a dipole-allowed transition\nfrom $^{2}E_{g}$-state to $^{2}A_{2u}$-state where the corresponding\n$a_{2u}$-level lies deeply inside the diamond valence band. Therefore, the\ntransition is broadened by the diamond band. At higher excitation power of 10\nmW we indicate signs of a parity-conserving transition at ~2.03 eV supported by\nsaturation measurements. For GeV$^{-}$ we demonstrate that the PLE spectrum is\nin good agreement with the mirror image of the PL spectrum of the zero-phonon\nline (ZPL). Experimentally we do not observe a higher lying energy level up to\na transition wavelength of 460 nm. The observed PL spectra are identical,\nindependent of excitation wavelength, suggesting a rapid decay to $^{2}E_{u}$\nexcited state and followed by optical transition to $^{2}E_{g}$ ground state.\nOur investigations convey important insights for future quantum optics and\nquantum sensing experiments based on SiV$^{-}$ center and GeV$^{-}$ center in\ndiamond.\n