Multicolor emitting luminescent MgO nanocubes for implication in ratiometric optical thermometry

Abstract

Optical thermometry employing dual emission from two distinct wavelengths for sensing performances has advantages over conventional thermometers due to the self-reference and noninvasive mode of operation. Here, we have demonstrated the synthesis of the multiple colors emitting luminescent MgO nanocubes and explored their temperature-dependent tunable emissions for application in intensity ratio-based optical thermometry. MgO nanocubes are prepared by heating Mg metal ribbons at different temperatures in air ambient. The as-prepared nanocubes exhibit two distinguished photoluminescence emission bands under UV (355 nm) and visible (532 nm) excitations. An excitation and synthesis condition-dependent multicolor emissions are observed in the visible to NIR regions due to the presence of various intermediate defect levels within the band gap of the materials. A temperature-dependent tunable dual emission is realized for different nanocubes, where the two peaks respond to the applied temperature differently, forming an isosbestic point. The difference in the temperature dependency of the two peaks is essential for the fluorescence intensity ratio-based optical thermometry application. The reason for the different responses of the two peaks is explained depending on the presence of the defect levels. From the temperature-dependent intensity ratio variation of MgO nanocubes, the highest sensitivity value of 6.79% K − 1 is achieved, which is very high compared to the various reported ratiometric sensors. The MgO nanocubes demonstrate better stability and reproducibility for application in the 83–513 K wide temperature range.