Cage Confinement Strategy in Perovskite-QDs@MOF for Boosting the Third-Order Nonlinear Optical Performance

Perovskite quantum dots (PeQDs) exhibit great potential in third-order nonlinear optics due to their unique optical properties and nanoscale dimensions. However, technical challenges still exist in controlling the size, morphology, and distribution. To address this issue, we utilize the confinement effect of the Cu-metal-organic framework (MOF) ({[Cu_1.75L_0.75(Pz-NH₂)_0.125(μ₃-O)_0.125(μ₂-OH)_0.25(H₂O)_0.375]·3CH₃CN} _n , where L = 5,5'-(1H-2,3,5-triazole-1,4-diyl)-diisophthalic acid) with cage-like pores to encapsulate ABBr₃-QDs (A = MA (methylammonium), FA (formamidine); B = Pb, Sn), resulting in uniformly dispersed ABBr₃-QDs within the Cu-MOF. The results of the third-order nonlinear optical (NLO) response show that, compared to PeQDs, the third-order NLO absorption of ABBr₃-QDs@Cu-MOF is enhanced by a factor of 6.36. Theoretical calculations and femtosecond transient absorption spectroscopy (fs-TAS) analysis reveal that the observed changes in NLO properties are primarily attributed to the redistribution of the electron clouds in PeQDs and Cu-MOF. This reconfiguration alters the band structure, facilitates the separation of free electron-hole pairs, and precisely controls the direction and relaxation time of free carrier transport, leading to a significant improvement in third-order NLO performance. Furthermore, by adjusting the composition of the cations, the third-order NLO signal of PeQDs@Cu-MOF can be effectively tuned. This study provides new insights into the development of high-performance third-order NLO materials.