  Spin defect centers with long quantum coherence times ($T_2$) are key
solid-state platforms for a variety of quantum applications. Recently, cluster
correlation expansion (CCE) techniques have emerged as a powerful tool to
simulate the $T_2$ of defect electron spins in these solid-state systems with
good accuracy. Here, based on CCE, we uncover an algebraic expression for $T_2$
generalized for host compounds with dilute nuclear spin baths, which enables a
quantitative and comprehensive materials exploration with a near instantaneous
estimate of the coherence. We investigate more than 12,000 host compounds at
natural isotopic abundance, and find that silicon carbide (SiC), a prominent
widegap semiconductor for quantum applications, possesses the longest coherence
times among widegap non-chalcogenides. In addition, more than 700 chalcogenides
are shown to possess a longer $T_2$ than SiC. We suggest new potential host
compounds with promisingly long $T_2$ up to 47 ms, and pave the way to explore
unprecedented functional materials for quantum applications.
