  Group IV color centers in diamond are among the most promising optically
active spin systems with strong optical transitions and long spin coherences.
The ground-state splitting of the center is particularly important to suppress
the interaction with coherence-limiting phonons, which improves the coherence
properties and sets the upper limit for the operating temperature. Negatively
charged silicon-vacancy centers have an ordinary ground-state splitting of only
48GHz, resulting in required temperatures below one Kelvin, which can only be
achieved by dilution refrigerators. Here, we increase the ground-state
splitting by up to an order of magnitude by induced strain in a single-crystal
diamond membrane. Furthermore, we demonstrate cavity-assisted spectroscopy
enabled by coupling the emitter ensemble with a selectable strain to the mode
of a Fabry-Perot microcavity. Calculation of the absorption cross-section
yields $\sigma_{ens} = $4.9*10^-11 cm^2. Together with the Purcell-enhanced
twofold reduction in emitter lifetime below 1ns, this makes the system a
promising spin-photon interface at moderate temperatures of 4K.
