Although monolayer transition metal dichalcogenides (TMDs) have direct bandgaps, the low room-temperature photoluminescence quantum yields (QYs), especially under high pump intensity, limit their practical applications. Here, we use a simple photoactivation method to enhance the room-temperature QYs of monolayer MoS₂ grown on to silica micro/nanofibers by more than two orders of magnitude in a wide pump dynamic range. The high-density oxygen dangling bonds released from the tapered micro/nanofiber surface are the key to this strong enhancement of QYs. As the pump intensity increases from 10⁻¹ to 10⁴ W cm⁻², our photoactivated monolayer MoS₂ exhibits QYs from ~30 to 1% while maintaining high environmental stability, allowing direct lasing with greatly reduced thresholds down to 5 W cm⁻². Our strategy can be extended to other TMDs and offers a solution to the most challenging problem toward the realization of efficient and stable light emitters at room temperature based on these atomically thin materials.

We report a waveguiding excitation-based approach for surface-enhanced fluorescence. As high as 17-fold enhanced fluorescence intensity of Rhodamine 6G molecules is realized by gold nanoparticles embedded in polymer nanofibers. The enhancement results not only from the spatial confinement of light by the nanofibers but also from the wavelength match among the excitation laser, the localized surface plasmon resonance of nanoparticles, and the absorption band of dyes. On the basis of the enhancement and high-efficient waveguiding regime, the required excitation power for detectable fluorescence is decreased to the 20 nW level, which is about 50 times lower than that by free-space excitation. These fluorophore/nanoparticle-doped nanofibers may find applications in compact and energy-efficient optical devices of chemical analysis and biosensing.

Photoluminescence intensity is widely used to infer exciton populations, yet the detected signal inherently convolves occupancy with radiative-rate modification and collection efficiency, making quantitative retrieval vulnerable to pump and system drifts. Here, we realize a dual-channel self-referenced scheme enabled by two nearly degenerate quasinormal modes in a hybrid microcavity. Their shared optical path provides common-mode observables (i.e., overall spectral and intensity drift) that track global thermo-optic and pump fluctuations, while their differential-mode observables (i.e., spectral splitting and mode-contrasted emission) remain highly sensitive to local gap dielectric perturbations and dipole-dependent radiative weights. Using temperature as a control parameter in monolayer WSe ₂ , we exploit this common/differential-mode framework to robustly invert the relative populations of excitons with out-of-plane (⊥) and in-plane (||) dipole transitions without external absolute calibration. At the temperature of ∼50 K, we obtain N _⊥ / N _|| ≈ 150 ± 30, coincident with the expected accumulation in the out-of-plane–emitting dark manifold. This internally referenced approach provides a practical route to drift-tolerant, dipole-resolved population metrology in nanogap photonic systems.

The compact cavity is always conducive to the integration and application of the devices based on whispering gallery modes. However, it is a challenge to strike a balance between the pursuit of a smaller cavity and higher quality. Here, we propose a low-loss cavity by combining a microsphere with a metal substrate, thereby compressing the cavity size by 24%. In addition, the substrate-modulated cavity is found to have a higher confinement factor and Purcell factor, showing the good prospect for realizing high-performance compact lasers.

Spin-forbidden dark excitons in monolayer transition metal dichalcogenides constitute a dominant hidden reservoir that governs exciton dynamics and many-body interactions. Yet determining the population distribution within this reservoir remains challenging because detected brightness conflates radiative-rate modification with collection efficiency, obscuring the link between intensity and population. Here we make this inverse problem well posed by calibrating the position- and orientation-resolved detection response. Combining microsphere-enabled k-space folding with Green-tensor quasinormal-mode calibration, we decouple radiative-rate modification from collection efficiency. We extract a room-temperature dark-to-bright population ratio ND/NB = 4.3, consistent with a near-thermalized manifold under continuous-wave excitation. This calibrated population metric provides a quantitative thermodynamic benchmark for the dark reservoir and interaction-driven 2D exciton phases.