  We report a giant thermal shift of $2.1 \,$MHz/K related to the excited-state
zero-field splitting in the silicon vacancy centers in 4H silicon carbide. It
is obtained from the indirect observation of the optically detected magnetic
resonance in the excited state using the ground state as an ancilla.
Alternatively, relative variations of the zero-field splitting for small
temperature differences can be detected without application of radiofrequency
fields, by simply monitoring the photoluminescence intensity in the vicinity of
the level anticrossing. This effect results in an all-optical thermometry
technique with temperature sensitivity of $100 \,$mK/Hz$^{1/2}$ for a detection
volume of approximately $10^{-6} \,$mm$^{3}$. In contrast, the zero-field
splitting in the ground state does not reveal detectable temperature shift.
Using these properties, an integrated magnetic field and temperature sensor can
be implemented on the same center.
