  We develop a two-color thermometry (TCT) phosphor based on
[Y$_{1-x}$Dy$_x$(acetylacetonate)$_3$(1,10-phenanthroline)]
([Y$_{1-x}$Dy$_x$(acac)$_3$(phen)]) molecular crystals for use in heterogeneous
materials. We characterize the optical properties of
[Y$_{1-x}$Dy$_x$(acac)$_3$(phen)] crystals at different temperatures and Dy
concentrations and find that the emission is strongly quenched by increasing
temperature and concentration. We also observe a broad background emission (due
to the ligands) and find that [Y$_{1-x}$Dy$_x$(acac)$_3$(phen)] photodegrades
under 355 nm illumination with the photodegradation resulting in decreased
luminescence intensity. However, while decreasing the overall emission
intensity, photodegradation is not found to influence the integrated intensity
ratio of the ${}^4I_{15/2} \rightarrow {}^6H_{15/2}$ and ${}^4F_{9/2}
\rightarrow {}^6H_{15/2}$ transitions. This ratio allows us to compute the
temperature of the complex Based on the temperature dependence of these ratios
we calculate that [Y$_{1-x}$Dy$_x$(acac)$_3$(phen)] has a maximum sensitivity
of 1.5 \% K$^{-1}$ and our TCT system has a minimum temperature resolution of
1.8 K. Finally, we demonstrate the use of [Y$_{1-x}$Dy$_x$(acac)$_3$(phen)] as
a TCT phosphor by determining a dynamic temperature profile using the emission
from [Y$_{1-x}$Dy$_x$(acac)$_3$(phen)].
