  We develop Dy$^{3+}$-doped yttrium complexes for use as two-color thermometry
(TCT) phosphor molecular crystals in heterogeneous materials. These complexes
include: Dy:Y(acac)$_3$(phen), Dy:Y(hfa)$_3$(DPEPO), Dy:Y(4-BBA)$_3$(TPPO),
Dy:Y(acac)$_3$, and Dy:Y(acac)$_3$(DPEPO), where the Dy/Y ratio is 1:9. We
characterize the materials' photoluminescence at different temperatures to
determine the TCT calibration parameters and the degree to which thermal
quenching influences the emission. From this data we observe a link between the
excited state lifetime at room temperature and the degree to which the material
is susceptible to thermal quenching (i.e. materials having long room
temperature lifetimes are more resistant to thermal quenching than materials
with short room temperature lifetimes). Of the five complexes tested we find
that Dy:Y(acac)$_3$(DPEPO) has the best thermal performance, with the most
likely source of improvement being DPEPO's compact rigid structure. This
rigidity helps with energy transfer to the Dy$^{3+}$ ion, suppresses
non-radiative loss modes, and reduces exciplex formation.
