Upconversion Luminescence and Discussion of Sensitivity Improvement for Optical Temperature Sensing Application

Upconversion (UC) based luminescent materials have promising applications in noncontact temperature sensors. How to improve the sensitivity is one main object at present. This work presented several strategies for optical temperature sensing based on UC spectra of the Y₂WO₆:Yb³⁺-Er³⁺/Ho³⁺/Tm³⁺ phosphors. The improvement for the relative (<i>S</i>_R) and absolute (<i>S</i>_A) sensitivities were discussed by using a fluorescence intensity ratio technique. It includes thermally coupled levels (TCLs) and non-TCLs. It was proposed that a piecewise expression could be employed to achieve high <i>S</i>_A value for TCLs. However, improving the <i>S</i>_R value is limited for TCLs. With regard to the non-TCLs, <i>S</i>_R and <i>S</i>_A are not restricted, but not easy to be improved synchronously. On the other hand, the morphology and UC spectra of the samples were also studied. The above investigation could be instructive to develop new luminescent materials with high sensitivity

Impact of Polar Edge Terminations of the Transition Metal Dichalcogenide Monolayers during Vapor Growth

The polar edges of two-dimensional monolayer transition metal dichalcogenides (TMD) and their alloys are examined by combined theoretical (density functional theory) and experimental approaches. For these polar edges, the growth reaction energies between different edge terminations are considered instead of the surface free energies. Due to different energy evolutions during growth on the zigzag edges between MoS₂ and WS₂, the S-ZZ edges in the WS₂ monolayer flakes more easily decompose into sawtooth-like edges in M-ZZ type as compared to the MoS₂ monolayer; thus, the hexagonal morphology can be seen more often in WS₂. Moreover, the observed anisotropic short-range order in the MoS₂/WS₂ alloys is originated from the freezed edge configurations during growth, explainable by the growth kinetics and thermodynamics of the Mo-ZZ-edges. The determination of the growing edge terminations is of great importance for the controllable synthesis of the emergent two-dimensional TMD materials