Room temperature multi-phonon upconversion photoluminescence in monolayer semiconductor WS2

Abstract

Photon upconversion is an anti-Stokes process in which an absorption of a photon leads to a reemission of a photon at an energy higher than the excitation energy. The upconversion photoemission has been already demonstrated in rare earth atoms in glasses, semiconductor quantum wells, nanobelts, carbon nanotubes and atomically thin semiconductors. Here, we demonstrate a room temperature upconversion photoluminescence process in a monolayer semiconductor WS2, with energy gain up to 150 meV. We attribute this process to transitions involving trions and many phonons and free exciton complexes. These results are very promising for energy harvesting, laser refrigeration and optoelectronics at the nanoscale.

Anti‐Stokes Photoluminescence of Monolayer WS2

“…We note that during writing of the manuscript, similar results have been reported for WS 2 . The authors observe anti‐Stokes luminescence in an hBN‐encapsulated sample at temperatures as low as 7 K using high excitation powers of up to 4 mW.…”

Band nesting and exciton spectrum in monolayer MoS2

“…From theoretical point of view, it is well-known that obtaining numerical solutions of Bethe-Salpeter equation is computationally challenging due to poor scaling with respect to increasing mesh of k-points discretizing the first Brillouin zone 27,42 . This problem becomes even more severe when larger, experimentally relevant optical complexes [49][50][51][52] are considered in reciprocal space via generalized Bethe-Salpeter equations, e.g. for trions [53][54][55] arXiv:2001.00443v2 [cond-mat.mtrl-sci] 29 Feb 2020 and biexcitons 56 .…”

Valley depolarization in downconversion and upconversion emission of monolayer WS2 at room temperature

“…Benefiting from enhanced photon-exciton [26][27][28][29][30][31][32][33][34][35][36][37] and phonon-exciton interaction strength [38][39][40][41] in a low dimensional scale, as observed in graphene and V-V binary materials [42,43], TMDCs are viewed as one promising platform for exploring UC PL at the monolayer limit. And there are some research studies reporting the UC PL observed in monolayer TMDCs, for example, two-photon absorption-induced UC PL of B-exciton at 4 K [44] and phonon-mediated doubly resonant UC PL with an energy gain of 30 meV up to 250 K [45] in monolayer WSe 2 , as well as multiphonon-induced UC PL with an energy gain of 150 meV in monolayer WS 2 at room temperature [46]. However, these research studies mainly focus on the excitonic conversion mechanism during the UC PL process, and the underlying dynamical transition process and intrinsic valley properties of monolayer TMDCs are unwittingly less concerned to some extent.…”