We investigate the intrinsic lead ion (Pb²⁺) emissions in zero-dimensional (0D) perovskite nanocrystals (NCs) using a combination of experimental and theoretical approaches. The temperature-dependent photoluminescence experiments for both “nonemissive” (highly suppressed green emission) and emissive (bright green emission) Cs₄PbBr₆ NCs show a splitting of emission spectra into high- and low-energy transitions in the ultraviolet (UV) spectral range. In the nonemissive case, we attribute the high-energy UV emission at approximately 350 nm to the allowed optical transition of ³P₁ to ¹S₀ in Pb²⁺ ions and the low-energy UV emission at approximately 400 nm to the charge-transfer state involved in the 0D NC host lattice (D-state). In the emissive Cs₄PbBr₆ NCs, in addition to the broad UV emission, we demonstrate that energy transfer occurs from Pb²⁺ ions to green luminescent centers. The optical phonon modes in Cs₄PbBr₆ NCs can be assigned to both Pb–Br stretching and rocking motions from density functional theory calculations. Our results address the origin of the dual broadband Pb²⁺ ion emissions observed in Cs₄PbBr₆ NCs and provide insights into the mechanism of ionic exciton–optical phonon interactions in these 0D perovskites.

中文翻译：

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零维Cs ₄ PbBr ₆纳米晶体中的本征铅离子发射。

我们结合实验和理论方法，研究零维（0D）钙钛矿纳米晶体（NCs）中的固有铅离子（Pb ²⁺）排放。Cs ₄ PbBr ₆ NCs的“非发光”（高度抑制的绿色发射）和发光（明亮的绿色发射）的随温度变化的光致发光实验表明，发射光谱在紫外（UV）光谱中分为高能和低能跃迁范围。在非辐射情况下，我们将大约350 nm处的高能UV发射归因于Pb ^2+中允许的³ P ₁到¹ S _0的光学跃迁离子和低能量UV发射到0D NC主晶格中所涉及的电荷转移状态（D态）大约为400 nm。在发射的Cs ₄ PbBr ₆ NCs中，除了宽泛的UV发射外，我们还证明了能量从Pb ²⁺离子转移到绿色发光中心。通过密度泛函理论计算，可以将Cs ₄ PbBr ₆ NCs中的光学声子模式分配给Pb-Br拉伸和摇摆运动。我们的结果解决了在Cs ₄ PbBr _6中观察到的双宽带Pb ²⁺离子发射的起源 NCs为这些0D钙钛矿中离子激子与光子声子相互作用的机理提供了见解。