Fig. 6: Optical-gain responses.

a Transient absorption (TA) spectroscopic data of CsPbI₂Br/WSe₂ heterostructure with photoexcitation at 0.8 P_th, P_th represents the corresponding lasing threshold. b The stimulated emission (SE) feature in TA map, is manifested as a pronounced bleach signal under 1.2 P_th fluence. c, d Carrier density-dependent nonlinear absorption spectra of CsPbI₂Br/WSe₂ heterostructure and CsPbI₂Br nanoplate, respectively, which were recorded at a delay time of ∼3 ps. e TA kinetics plots of the SE dynamics at 660 nm (in resonance with the lasing peak) in the form of −Δα/α₀ versus time delay. The \(\alpha\) and \({\alpha }_{0}\) are the absorption coefficients under pumped and unpumped conditions, respectively. The gain decay lifetime corresponds to −Δα/α₀ > 1, demonstrating a prolonged gain lifetime in CsPbI₂Br/WSe₂ heterostructure. f Comparison of representative optical gain values reported for perovskite-based materials^{50,51,52,53,54,55,56,57,58}. The green and blue shaded areas represent the reported gain coefficients, and the red shaded area highlights our result, which belongs to the premier echelon. The dashed lines classify the reported perovskite gain materials, most of which focus on the green (CsPbBr₃) emitters.