We study monotonicity of eigenvalues of the Schrödinger-type operator
, where
is a constant, along the Ricci–Bourguignon flow. For
, we
derive monotonicity of the lowest eigenvalue of the Schrödinger-type operator
,
which generalizes some results of Cao (2008). As an application, we rule out
nontrivial compact steady breathers in the Ricci–Bourguignon flow. For
, we
derive monotonicity of the first eigenvalue of the Laplacian, which generalizes some
results of Ma (2006).