The study investigates the elementary excitations of single-photon emitters (SPEs) in hexagonal boron nitride (hBN) using resonant inelastic X-ray scattering (RIXS) and photoluminescence (PL) spectroscopy. The researchers identify an excitation at 285 meV in defective hBN, which propagates up to 2.3 eV through multiple harmonics. This elementary excitation is correlated with a variety of SPEs observed in the visible spectrum. The analysis of PL spectra reveals that the harmonics observed in RIXS can be explained by fundamental transitions involving donor-acceptor pairs (DAPs) with energies matching the harmonics at $n = 5 - 8$. The study highlights the importance of N π* anti-bonding orbitals in shaping the electronic states of the emitters and provides new insights into quantum emission in low-dimensional materials. The findings suggest that the elementary excitation at 285 meV is responsible for the wide range of quantum emission energies in hBN, and the DAP model successfully explains the observed harmonics. This work establishes RIXS as a valuable tool for understanding and characterizing low-dimensional photonic quantum materials.The study investigates the elementary excitations of single-photon emitters (SPEs) in hexagonal boron nitride (hBN) using resonant inelastic X-ray scattering (RIXS) and photoluminescence (PL) spectroscopy. The researchers identify an excitation at 285 meV in defective hBN, which propagates up to 2.3 eV through multiple harmonics. This elementary excitation is correlated with a variety of SPEs observed in the visible spectrum. The analysis of PL spectra reveals that the harmonics observed in RIXS can be explained by fundamental transitions involving donor-acceptor pairs (DAPs) with energies matching the harmonics at $n = 5 - 8$. The study highlights the importance of N π* anti-bonding orbitals in shaping the electronic states of the emitters and provides new insights into quantum emission in low-dimensional materials. The findings suggest that the elementary excitation at 285 meV is responsible for the wide range of quantum emission energies in hBN, and the DAP model successfully explains the observed harmonics. This work establishes RIXS as a valuable tool for understanding and characterizing low-dimensional photonic quantum materials.