Thermally Robust Dy3+-activated Sc2Mo3O12 Phosphor for Sustainable WLEDs Lighting and Phase Transition-Enabled Visual Cryogenic Thermometry

Abstract

The development of phosphors exhibiting negative-thermal expansion (NTE) is urgent for achieving thermally robust luminescence performance of phosphor-converted white light-emitting diodes (pc-WLEDs). The current pc-WLEDs suffer from poor thermal stability, suboptimal color rendering index (CRI) due to blue-light exposure, and high correlated color temperature (CCT). Herein, we developed a promising Sc2Mo3O12:Dy3+ phosphor with bright yellow-white emission upon ultraviolet (UV) and near-UV light excitation. Local structure analysis using extended X-ray absorption fine structure (EXAFS) spectroscopy confirmed the occupancy of Dy3+ ions at octahedral Sc3+ sites. Temperature-dependent in-situ X-ray diffraction study revealed a strong NTE effect in Sc2Mo3O12. Temperature-dependent photoluminescence studies demonstrated the excellent luminescence thermal stability of Sc2Mo3O12:Dy3+ phosphor (91.4% @480 K) due to enhanced structural rigidity and reduced non-radiative decay as a result of thermally induced lattice compaction. The influence of the host’s low-temperature phase transition on Dy3+ luminescence was examined at cryogenic temperature conditions. Further, we demonstrated the fabrication of three prototype pc-WLEDs by coating the Sc2Mo3O12:Dy3+ phosphor onto UV-LED chip with tunable WLEDs parameters i.e., CIE, CCT, and luminous efficacy, which strengthens its suitability for commercial lighting. The optical thermal sensing based on charge transfer red-shift and phase transition-induced luminescence have been demonstrated with high relative sensitivity (Sr) values of 2.30 (70 K) and 1.14% K-1 (300 K) across different temperature regimes, from cryogenic to high-temperature conditions, respectively, with visual color tuning. This work highlights the potential of NTE-active hosts in designing pc-WLED phosphors with enhanced thermal stability to advance the commercialization of sustainable WLED lighting, and offers opportunities for flexible thermal sensing in complex environments.