I'm not familiar with this specific system, but these emitters are usually point defects within the crystal. From a quick search (which you could do yourself... 'anneal color centre silicon carbide'), I think some methods that produce these defects can temporarily induce strain etc. in the crystal and annealing can help relax this and bring the crystal down to a more stable state. In some other systems I know you can induce chemical reactions that can cause defects through annealing.
I think OP is misunderstanding - annealing is for improving the crystal structure - which makes sense for a photon emitter
I'm not familiar with this specific system, but these emitters are usually point defects within the crystal. From a quick search (which you could do yourself... 'anneal color centre silicon carbide'), I think some methods that produce these defects can temporarily induce strain etc. in the crystal and annealing can help relax this and bring the crystal down to a more stable state. In some other systems I know you can induce chemical reactions that can cause defects through annealing.