# Two-color Thermosensors based on [Y$_{1-X}$Dy$_X$(acetylacetonate)$_3$(1,10-phenanthroline) Molecular Crystals

## TL;DR

This study develops a two-color thermometry phosphor using molecular crystals with Dy doping, demonstrating temperature sensing capabilities through emission ratios, despite photodegradation effects, with potential applications in heterogeneous materials.

## Contribution

We introduce a novel Dy-doped molecular crystal-based TCT phosphor and analyze its temperature-dependent optical properties and stability for thermometry applications.

## Key findings

- Emission is quenched by temperature and Dy concentration.
- The emission ratio remains stable despite photodegradation.
- Maximum sensitivity of 1.5% K$^{-1}$ for temperature measurement.

## Abstract

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)].