Fig. 1. (Color online) Intriguing applications based on atomically thin MoSe₂, including light-emitting diodes, single-photon emitters, and coherent light sources.

Fig. 2. (Color online) (a−d) ARPES spectra of MoSe₂ thin layers with different thicknesses^[37]. (e) Schematic of band structures of MoX₂ and WX₂ monolayers^[40]. (f) Classification of excitonic quasiparticles, including neutral excitons (X⁰), charged excitons (X*), biexcitons (XX), and interlayer excitons (X^I).

Fig. 3. (Color online) (a) Schematic, optical image, and PL mapping of the freestanding bilayer MoSe₂^[47]. (b) The PL spectra both of the freestanding bilayer MoSe₂ and the one on SiO₂ substrate, where the "X", "T", and "A" refer to the emission peak of biexcitons, trions, and excitons, respectively^[47]. (c) The relationship between PL intensities of A and X^[47]. (d) Illustration of different kinds of excitons in real space^[15]. (e) Measured and simulated reflection contrast spectra (R_sam/R_sub) of h-BN-encapsulated monolayer MoSe₂^[15]. (f) Measured and simulated reflection contrast spectra of h-BN-encapsulated bilayer MoSe₂^[15].

Fig. 4. (Color online) (a) PL spectra of monolayer MoSe₂ at different temperatures^[48]. (b) Two pronounced PL peaks of monolayer MoSe₂ at 20 K: the higher-energy X⁰ and the lower-energy X* at 1.659 and 1.63 eV, respectively. The inset indicates the X* binding energy of approximately 30 meV^[57]. (c) Temperature-dependent PL spectra of monolayer MoSe₂^[57]. (d) PL spectra of monolayer MoSe₂ measured in the temperature range from 0 to 300 K^[59]. (e) A and B excitonic energies at different temperatures, which were fitted by the Varshni relationships^[59].

Fig. 5. (Color online) (a) PL and reflectance contrast (RC) spectra of h-BN encapsulated monolayer MoSe₂ at 10 K, where the X^b and X^T represent the bright neutral excitons and the trions bands, respectively^[55]. (b) PL intensity map of encapsulated monolayer MoSe₂ at different in-plane magnetic fields^[55]. (c) PL spectra of samples measured at 0 and 31 T^[55]. (d) Magnetic field dependence of PL intensity map of monolayer MoSe₂^[56]. (e) Gate voltage dependencies of PL intensities for X* and X⁰, respectively^[57]. (f) Calculation results of the exciton band structures of bright KK and dark KΛ in the MoSe₂ bilayer^[54].

Fig. 6. (Color online) (a) Schematic of a monolayer-MoSe₂ coupled plasmonic microcavity^[26]. (b) Simulated scattering spectra of MoSe₂ coupled microcavities, where the blue dashed and the red solid lines correspond to the MoSe₂ monolayers without/with the Al₂O₃ coating, respectively. The yellow PL spectrum is from the MoSe₂ monolayer on a quartz substrate^[26]. (c) The distributions of surface charge and electric field^[26]. (d) Illustration of a MoSe₂ monolayer encapsulated by h-BN on SiO₂/Si^[7]. (e) The PL spectrum of MoSe₂ encapsulated by h-BN layers exhibits the neutral (X) and the charged (T) exciton bands at 7 K^[7]. (f) The bottom h-BN thickness dependence of X radiative lifetime of monolayer MoSe₂. The red dotted line shows the intensities of the electromagnetic field. The inset presents the normalized time-resolved photoluminescence (TRPL) intensities with different bottom h-BN layers^[7]. (g) Diagram of the WSe₂/MoSe₂ heterostructure coupled with Au nanodisks on the PPhC^[30]. (h) The energy dependences of the averaged Purcell factors of γ_mean and the coefficients of σ(γ)/γ_mean, respectively^[30]. (i) The left panel is the typical interlayer excitons in a heterostructure and the right panel represents long-lived interlayer excitons in a heterostructure coupled with the nano-photonic microcavity^[30].

Fig. 7. (Color online) (a) Illustration of exciton−photon interaction in the case of an F−P microcavity system. (b) Schematic of angle-resolved optical response in the exciton−photon strong coupling regime, exhibiting the anti-crossing characteristics^[77]. (c) Structures of monolayer MoSe₂ integrating into an open cavity (left) and a monolithic cavity (right), respectively^[33]. (d) Schematic of the self-hybridized F−P cavity in bulk TMDs^[78].

Fig. 8. (Color online) Various polaritons are formed in TMDs-coupled cavities, including EPs, PEPs, and phonon-polaritons.

Fig. 9. (Color online) (a, b) A tunable hemispherical cavity coupled with the MoSe₂/hBN heterostructures formed by a planar and a concave DBR and the corresponding strong coupling behavior with a Rabi splitting of 29 meV, respectively^[27]. (c) Schematic of a MoSe₂/h-BN heterostructure embedded in the F−P microcavity^[34]. (d) Angle-resolved photoluminescence (ARPL) image of a MoSe₂/h-BN heterostructure in a monolithic cavity^[34]. (e) Schematic of a high-quality F−P microcavity device embedded with a h-BN encapsulated monolayer MoSe₂^[29]. (f) Measured and fitted reflection contrast spectra of the bare cavity mode and the one with hBN layers^[29]. (g) ARR map of a MoSe₂/WS₂ heterostructure measured at 5 K^[8].

Fig. 10. (Color online) (a) Schematic of the microcavity device embedded with a MoSe₂ monolayer and four GaAs quantum wells^[35]. (b) The calculated reflectivity spectrum of the Tamm-plasmon microcavity^[35]. (c) ARPL of the Tamm microcavity of a MoSe₂ monolayer at 4 K^[35]. (d) Illustration of a MoSe₂ monolayer encapsulated by h-BN is inserted into an F−P microcavity structure and the optical microscope image of the full device^[23]. (e) The pump-power dependent polariton dispersions for a MoSe₂ microcavity^[23].

Fig. 11. (Color online) (a) Illustration of the structure of a Tamm microcavity^[33]. (b) A Tamm-plasmon microcavity employs a monolayer MoSe₂ and four embedded GaAs quantum wells as active layers^[36]. (c) Power dependences of PL intensity and linewidth for MoSe₂ monolayer, respectively^[36]. (d) Blueshift of the polariton mode as a function of excitation power^[36]. (e) Schematic of a MoSe₂-integrated Tamm microcavity^[94]. (f) ARPL map of a Tamm microcavity, in which the UPB and LPB are indicated by black dotted lines^[94].

Fig. 12. (Color online) (a) The structure of MoSe₂/WSe₂ heterostructure device^[18]. (b) Illustration of Nb-doping mechanism^[19]. (c) The rectifying behavior of p−n diode based on MoSe₂^[19]. (d) The formation process of a p−i−n junction^[3]. (e) Light-emitting zones of WSe₂, MoSe₂ and WS₂ devices, respectively^[3]. (f) Illustration of a two-terminal LED^[3].

Fig. 13. (Color online) (a) PL intensity map of MoSe₂ monolayer in the range of 683−855 nm^[21]. (b) PL spectra of two samples on gold substrates^[21]. (c) PL spectra for discrete QDA, QDB, and QDC measured at varied magnetic fields^[21]. (d) Illustration of MoSe₂ monolayer covering the holes with different sizes to create exciton traps^[20]. (e) PL spectra collected at a quantum emitter and a flat region^[20]. (f) PL spectra of Moiré-confined interlayer excitons^[121].

Fig. 14. (Color online) (a) Schematic of a WSe₂/MoSe₂ heterostructure on the silicon−nitride grating cavity system^[22]. (b) Band alignment of a WSe₂/MoSe₂ heterostructure^[22]. (c) The pump power dependences of photon occupancy (I_p) and linewidth^[22]. (d) Optical image of the MoSe₂/h-BN quantum wells^[27]. (e) Illustration of a monolayer MoSe₂ integrated with the photonic crystal microcavity^[81]. (f) ARR of Dodecanol/MoSe₂/Dodecanol-PC on the device with the detuning value of 0.1 ± 0.2 meV approximately^[81].

Table 1. Strong coupling regime in atomically thin MoSe₂.