When is a p-block a q-block?
Gabriel Navarro and Wolfgang Willems
Proc. Amer. Math. Soc. 125 (1997), 1589-1591.

Abstract. Let $p$ and $q$ be distinct prime numbers and let $G$ be a finite 
group. If $B_p$ is a $p$-block of $G$ and $B_q$ is a $q$-block, we study when 
the set of ordinary irreducible characters in the blocks $B_p$ and $B_q$
coincide.