Anti‐Stokes Photoluminescence of Monolayer WS₂

Abstract

Anti‐Stokes photoluminescence excitation of a WS2 monolayer flake between 10 and 300 K is reported herein. Even with continuous‐wave lasers at low power, the emission of the exciton at excitation 100 meV below its emission energy at room temperature is observed. A mechanism which involves the trions as the intermediate state is proposed, leading to an efficient up‐conversion process. In addition, it is demonstrated that phonons are the source of the additional energy needed by the system. Overall, the results provide evidence that anti‐Stokes luminescence in transition metal dichalcogenides is very efficient.

Up-conversion photoluminescence of transition metal chalcogenide monolayers under high pressure

“…At room temperature, Jadczak et al found that the power dependence slope of the UPL intensity is close to 1 as well, when the excitation is at A1s energy of WS2. These measurements provide strong evidence that the UPL process in our work is the phononassisted linear up-conversion process [13,14,15,17,23].…”

“…There have been many studies on UPL of TMDCs, which has been realized by resonant excitation of the ground exciton states [10,11,12] at the cryogenic temperature. Alternatively, by an off-resonance excitation at the lower energy than the exciton states, the phononassisted up-conversion process could be achieved [13][14][15][16][17], which is promising to realize the application of photodetector [17,18,19]. The detailed physical mechanisms of UPL under various extreme conditions are required for multi-environment optoelectronic applications.…”

Photoluminescence upconversion of 2D materials and applications

“…The presence of real intermediate states can be revealed by PLE spectroscopy, which has been discussed in section 2.1 (phonon absorption). When the excitation energy is below the energy of the real intermediate states, the upconversion intensity declines abruptly [75,92].…”

“…At low laser power before saturation, the PL intensity of two-photon upconversion involving real intermediate states usually shows a quadratic dependence on the excitation power (α ≈ 2) [68,71,73,74,92,105,108]. Further increasing the excitation power results in the full occupation of the intermediate states.…”

“…Photoluminescence (PL) upconversion is a phenomenon involving light-matter interactions, where the energy of emitted photons is higher than that of the excitation photons [64][65][66][67]. This phenomenon has been extensively reported in dye molecules [68], nanotubes [66], quantum wells [69,70], quantum dots [71][72][73][74][75][76], lead-halide perovskites [77][78][79][80][81][82][83][84][85], TMDCs [65,67,[86][87][88][89][90][91][92], and h-BN [64,93]. The potential applications in bioimaging [94,95], optical refrigeration in semiconductors [78,96], and upconversion optoelectronic devices [97][98][99][100][101] are the motivation for the study of PL upconversion.…”