Four-Mode High-Performance Optical Thermometer in Eu³⁺ Monodoped MgNb₂O₆ Phosphor and Multifunctional Applications

Noncontact optical temperature measurement has attracted considerable attention due to its crucial applications across various fields. However, the demand for highly sensitive optical thermometric materials remains pressing. This study introduces an ultrasensitive charge transfer band-based optical temperature sensing system utilizing Eu³⁺ monodoped MgNb₂O₆ phosphor, effectively circumventing the limitations associated with traditional thermally coupled energy levels. By utilizing the luminescence intensity ratio based on excitation and emission spectra, we introduced three measurement modes; the optical thermometer exhibited a maximum relative sensitivity of 4.24% K^-1 (300 K) and an absolute sensitivity of 2.99% K^-1 (570 K), surpassing the sensitivity of most optical thermometers of the same type. Furthermore, by employing the shift of charge transfer band peak position as a measurement parameter, we developed a novel optical thermometer with a sensitivity (S_w) of 0.064 nm·T^-1. This material, exhibiting high brightness and high-purity red emission due to the efficient energy pathway provided by the ultraviolet absorption of the matrix, emerges as a promising candidate for LED applications. Additionally, ink and PDMS flexible films made of MgNb₂O₆:Eu³⁺ phosphor were prepared to illustrate potential applications in anticounterfeiting and encryption. All the studies demonstrate that the MgNb₂O₆:Eu³⁺ material is a promising candidate in the field of multimodal high-performance and multifunctional optical thermometers.