Optical Thermometry in Monolayer WS2: Raman and Photoluminescence Spectroscopy from 5 K to 1273 K

Reliable temperature measurement is essential for characterizing and engineering two-dimensional (2D) semiconductor devices, yet optical thermometry of 2D materials has so far been demonstrated only over narrow temperature windows spanning a few hundred kelvin. Here, we establish a comprehensive optical thermometry framework for monolayer WS2 from 5~K to 1273~K. We show that: (i) the out-of-plane A1g Raman mode shifts linearly with temperature above 100~K, with a slope of -0.0138 cm^{-1}/K in non-encapsulated WS2 (fitted over 298-1223~K) and a measurably smaller slope of -0.0121 cm^{-1}/K in an hBN-encapsulated sample (fitted over 100-1273~K); (ii) photoluminescence spectra measured over the same 5--1273~K range provide an independent optical indicator of the temperature: the neutral-exciton emission redshifts continuously with temperature and is well described by the semi-empirical Pässler model. The two indicators probe distinct physical mechanisms, lattice anharmonicity and bandgap renormalization, and together provide contact-free thermometry for monolayer WS2 from 5~K to 1273~K, an approach applicable to 2D semiconductors more broadly.