Chemical Control of Zero-Phonon Line Wavelength in Diamond Color Centers for Telecom-Band Emission.

Solid-state color centers in diamond are promising candidates for quantum communication, yet the absence of intrinsic emitters operating in the telecom band has remained a fundamental bottleneck for scalable fiber-based quantum networks compatible with the existing optical fiber infrastructure. Here, by combining first-principles calculations with group-theoretical analysis, we establish a general chemical design rule that links the chemical nature of substitutional impurities to the zero-phonon line (ZPL) wavelengths of vacancy-impurity-vacancy centers in diamond. This framework shows that impurity atomic size and orbital energies act together to tune the ZPL. Specifically, heavy elements with fully filled d orbitals yielding shorter-wavelength emission, while lighter elements lacking occupied d orbitals, generate longer-wavelengths. Guided by this principle, we identify the negatively charged vacancy-magnesium-vacancy (MgV) center as an ideal telecom-band emitter at 1448 nm, exhibiting outstanding optical coherence, minimal electron-phonon coupling, and a remarkably high Debye-Waller factor of 94.1%. These results provide not only a long-sought candidate for fiber-compatible quantum emitters but also a transferable design paradigm for tailoring optical transitions in wide-bandgap hosts, paving the way for material discovery in solid-state quantum technologies.