Fig. 4
From: Room temperature multi-phonon upconversion photoluminescence in monolayer semiconductor WS2
Excitation power dependence of the upconversion photoemission. a Comparison of the spectra in monolayer WS2 deposited on SiO2/Si substrate, recorded in ambient (black line) and vacuum (red line), excited with the same incident photon energy 1.890 eV and power, at 295 K. b Comparison of the anti-Stokes Raman spectra measured in ambient (black line) and vacuum (red line), obtained by subtracting the emission from the corresponding UPC spectra in a. c, d examples of spectra excited with different laser powers, recorded in ambient and vacuum, respectively. e The integrated upconversion photoemission intensity plotted as a function of excitation power density for total spectra recorded in ambient (black circles), in vacuum (magenta stars), for X peak in vacuum (red points), for T peak in vacuum (blue point)
