Advanced Research Centre for High Energy Materials (ACRHEM), University of Hyderabad, Hyderabad 500046, Telangana, India.
Nanoscale. 2019 Jan 17;11(3):945-954. doi: 10.1039/c8nr06969g.
Lead halide perovskite nanocrystals (NCs) apart from their overwhelming optoelectronic applications have recently demonstrated promising nonlinear optical (NLO) properties such as strong two-photon absorption cross-sections (∼105 GM), two-photon fluorescence, and saturable absorption even at very high peak intensity. Zero-dimensional perovskite-related materials (0-D PRMs) are a new class of materials offering a high exciton binding energy (Eg ≥ 180 meV) with a strong photoluminescence (PL) quantum yield in few cases. Herein, we report the broadband third-order NLO properties of phase pure Cs4PbBr6 0-D PRM achieved using the Z-scan and degenerate four-wave mixing techniques in the femtosecond regime. Considering the growing content of the fluorescent and non-fluorescent forms of this material, we have performed our studies on both of them. These perovskite NCs exhibited strong multi-photon absorption properties in the near-infrared region with two-photon absorption (2PA) (cross-section, σ2 = 10-43-10-44 cm4 s equivalent to ∼106 GM) in the 500-800 nm region, three-photon absorption (3PA) (cross-section, σ3 ∼10-73 cm6 s2) in the 900-1200 nm region and four-photon absorption (4PA) (cross-section, σ4 ∼10-100 cm8 s3) in the 1300-1500 nm spectral region. These multi-photon absorption processes are explained using a simple band diagram. The measured NLO coefficients and cross-sections are fairly large when compared to some of the earlier reports on perovskite-based NCs. Cs4PbBr6 0-D PRM also demonstrated a large third-order NLO susceptibility χ(3) (∼10-7 esu), which can be attributed to the strong quantum confinement arising from spatially isolated, exciton containing individual [PbBr6]4- octahedron. These results clearly suggest the potential of 0D-PRMs in applications such as photonics and ultrafast all-optical switching devices.
卤铅钙钛矿纳米晶体（NCs）除了在光电应用方面具有压倒性优势外，最近还表现出了有前途的非线性光学（NLO）性质，例如强双光子吸收截面（∼105 GM）、双光子荧光和饱和吸收，即使在非常高的峰值强度下也是如此。零维卤铅钙钛矿相关材料（0-D PRMs）是一类新型材料，它们具有高激子结合能（Eg≥180 meV），在少数情况下具有很强的光致发光（PL）量子产率。在此，我们报告了在飞秒范围内使用 Z 扫描和简并四波混频技术实现的纯相 Cs4PbBr6 0-D PRM 的宽带三阶 NLO 性质。考虑到这种材料的荧光和非荧光形式的含量不断增加，我们对这两种形式都进行了研究。这些钙钛矿 NCs 在近红外区域表现出很强的多光子吸收性质，在 500-800nm 区域的双光子吸收（2PA）（截面，σ2=10-43-10-44 cm4 s 相当于 ∼106 GM），在 900-1200nm 区域的三光子吸收（3PA）（截面，σ3 ∼10-73 cm6 s2）和在 1300-1500nm 光谱区域的四光子吸收（4PA）（截面，σ4 ∼10-100 cm8 s3）。这些多光子吸收过程用一个简单的能带图来解释。与一些基于钙钛矿的 NCs 的早期报道相比，测量的 NLO 系数和截面相当大。Cs4PbBr6 0-D PRM 还表现出大的三阶 NLO 磁化率 χ(3)（∼10-7 esu），这可以归因于空间隔离的、包含激子的单个[PbBr6]4-八面体引起的强量子限制。这些结果清楚地表明了 0D-PRMs 在光子学和超快全光开关器件等应用中的潜力。
