Localized triplons and site stuffing in the quantum dimer magnet <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msub> <mml:mi>BiYbGeO</mml:mi> <mml:mn>5</mml:mn> </mml:msub> </mml:math>

Thermodynamic and muon spin relaxation measurements have recently highlighted ${\mathrm{BiYbGeO}}_{5}$ as a new example of a rare-earth-based quantum dimer magnet with isolated ${\mathrm{Yb}}^{3+}$ spin-1/2 dimers. However, direct spectroscopic evidence of the triplet excitations and measurements of the structural disorder are lacking. In this work, polycrystalline ${\mathrm{BiYbGeO}}_{5}$ was synthesized using conventional high-temperature solid-state methods and investigated via high-resolution neutron powder diffraction and inelastic neutron scattering. Diffraction measurements down to 58 mK reveal no signatures of magnetic order and indicate that nearly 20% of ${\mathrm{Yb}}^{3+}$ sites are replaced by nonmagnetic ${\mathrm{Bi}}^{3+}$, introducing significant structural disorder. Inelastic neutron scattering shows dispersionless triplon excitations, consistent with localized, noninteracting spin dimers. Fits to the triplet excitation spectrum with an XXZ-type anisotropic exchange give ${J}_{\text{XX}}=0.100(1)\phantom{\rule{0.28em}{0ex}}\text{meV}$ and ${J}_{\text{Z}}=0.202(1)\phantom{\rule{0.28em}{0ex}}\mathrm{meV}$. These findings establish ${\mathrm{BiYbGeO}}_{5}$ as a structurally disordered but magnetically well-isolated quantum dimer system, providing a model platform for studying the resilience of entangled spin states to site dilution.