Persistent Luminescence (PeL) is a phenomenon in which a material continues to emit light for extended period after removing the excitation source (X-rays, electrons, or ultraviolet/visible light). This effect arises from metastable localized electronic levels in the bandgap that temporarily store the excitation energy. While the majority of PeL materials (>75%) are oxides, recent studies have demonstrated the occurrence of PeL in bulk halide double perovskites (HDPs) as well. Notably, Cs₂(AgₓNa₁₋ₓ)InCl₆:Mn²⁺ single crystals (SCs) exhibit a persistent red emission (~620 nm) for over an hour after UV excitation. However, moving from bulk to nanostructured samples the PeL disappears). In this work, we investigate the impact of stoichiometry, size and shape on the PeL behavior of HDPs. We synthesized various compositions of Cs₂(AgₓNa₁₋ₓ)InCl₆:Mn²⁺ SCs and extended our study to their micrometric and nanometric counterparts, including nanocubes (NCs) and nanoplates (NPs). To understand the underlying mechanisms, we performed optical analyses, including photoluminescence excitation, photoluminescence, PeL, and thermally stimulated luminescence measurements across a broad temperature range (10 K–450 K). Since PeL is related to the presence of trapping sites, which may originate from local structural defects, we further investigated these defects using X-ray Powder Diffraction, Pair Distribution Function analysis (across 15 K and 373 K), and X-ray Absorption Near Edge Structure (XANES) spectroscopy at the K-edge of Mn (the emissive center) at three different temperatures: 15 K, 290 K and 430 K. Our results indicate a strong size-dependent behavior. We hypothesize that the PeL disappearance from bulk to nanocrystals is ascribed to differences in the position of the traps in the bandgap between bulk and nanostructured samples. In addition, from the XANES analysis, the pre-edge peak is broader for the bulk sample, so we hypothesize that in the bulk sample, Mn coexists in the 2+ and 3+ oxidation states, with the 3+ responsible for the PeL.
Investigating the persistent luminescence in Cs2(AgxNa1-x)InCl6:Mn2+ double perovskites
Emmanuela Di Giorgio;Marta Campolucci;Chiara Solinas;Maurizio Ferretti;Federico Locardi
2025-01-01
Abstract
Persistent Luminescence (PeL) is a phenomenon in which a material continues to emit light for extended period after removing the excitation source (X-rays, electrons, or ultraviolet/visible light). This effect arises from metastable localized electronic levels in the bandgap that temporarily store the excitation energy. While the majority of PeL materials (>75%) are oxides, recent studies have demonstrated the occurrence of PeL in bulk halide double perovskites (HDPs) as well. Notably, Cs₂(AgₓNa₁₋ₓ)InCl₆:Mn²⁺ single crystals (SCs) exhibit a persistent red emission (~620 nm) for over an hour after UV excitation. However, moving from bulk to nanostructured samples the PeL disappears). In this work, we investigate the impact of stoichiometry, size and shape on the PeL behavior of HDPs. We synthesized various compositions of Cs₂(AgₓNa₁₋ₓ)InCl₆:Mn²⁺ SCs and extended our study to their micrometric and nanometric counterparts, including nanocubes (NCs) and nanoplates (NPs). To understand the underlying mechanisms, we performed optical analyses, including photoluminescence excitation, photoluminescence, PeL, and thermally stimulated luminescence measurements across a broad temperature range (10 K–450 K). Since PeL is related to the presence of trapping sites, which may originate from local structural defects, we further investigated these defects using X-ray Powder Diffraction, Pair Distribution Function analysis (across 15 K and 373 K), and X-ray Absorption Near Edge Structure (XANES) spectroscopy at the K-edge of Mn (the emissive center) at three different temperatures: 15 K, 290 K and 430 K. Our results indicate a strong size-dependent behavior. We hypothesize that the PeL disappearance from bulk to nanocrystals is ascribed to differences in the position of the traps in the bandgap between bulk and nanostructured samples. In addition, from the XANES analysis, the pre-edge peak is broader for the bulk sample, so we hypothesize that in the bulk sample, Mn coexists in the 2+ and 3+ oxidation states, with the 3+ responsible for the PeL.
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