Room-temperature phosphorescence (RTP) from organic ionic crystals mainly related to molecular packing has attracted growing attention over a wide range of advanced applications. However, limited research has focused on improving the RTP performance of organic materials in their aggregated state. Herein, we utilize the layer-by-layer self-assembly of organic ammonium chloride salts to enhance the macroscopic performance and increase the phosphorescence lifetime by 1–2 orders of magnitude. Especially, the millimeter-sized large organic ionic crystal exhibits an obvious RTP emission (insensitive to air) with an ultralong lifetime of 1886 ms, exceeding most counterparts. Molecular dynamics simulations reveal that the compact intermolecular stacking isolates oxygen molecules from the phenyl groups (distributing the spin population in the triplet state), which effectively suppresses triplet quenching for large crystals. Furthermore, other organic ammonium chloride salts also confirm such a macrocrystal-sized dependence on phosphorescence lifetimes. This work provides an effective crystallization strategy to realize an ultralong RTP emission, along with an extensive modulation of luminescence lifetime potential for time-gated encryption.
In recent years, second near-infrared window emitting phosphors have gained widespread research interest due to their excellent tissue penetration and high imaging accuracy. In this work, a new type of Ba 2 Ti 1- x Mn x O 4+ x /2 (0.02 ≤ x ≤ 0.10) phosphors were successfully prepared by high-temperature solid-phase method and their potential in luminescence thermometry is evaluated. PL and PLE spectral analysis prove that the optimal Mn doping concentration is x = 0.03. The as-synthesized phosphors exhibit a broad excitation band of 550–1000 nm and a narrow emission band of 1170–1220 nm. The electronic structures of the original Ba 2 TiO 4 and Mn-doped Ba 2 TiO 4 were calculated and analyzed using the DFT + U method, which facilitates a better understanding of the impact of Mn doping on the luminescent properties of Ba 2 TiO 4 . The luminescence decay lifetime is measured to be 101.44 μs at room temperature, which is a giant enhancement compared to conventional nanosecond lifetime phosphor, indicating a progress in imaging accuracy. In addition, the as-synthesized phosphors maintain over 75 % of the maximum luminescence intensity within the physiological temperature range. The potential applications in luminescence temperature measurement were also analyzed by the LIR ratio method, and the relative sensitivity could reach 2.31 %K −1 at 283 K, which is a relatively high value in the second near-infrared window. Therefore, the as-synthesized Ba 2 Ti 1- x Mn x O 4+ x /2 (0.02 ≤ x ≤ 0.10) phosphors demonstrate great potential in NIR applications such as biological imaging and luminescent thermometry.
Cheng Xu,Haojie Liu,Zirun Peng,Yan Zhang,Na Liu,Shiheng Li,Zhong Lin Wang,Peizhong Feng
The output performance of triboelectric nanogenerators (TENGs) largely depends on the density of electrons on the surface of the triboelectric materials, which is usually generated by the direct contact of two solid materials. Here, a novel method is proposed to regulate the surface charges of materials without physical contact. A laser-tunable noncontact triboelectric nanogenerator (LTNC-TENG) is fabricated, enabling the dynamic regulation of the surface states of materials through laser irradiation to optimize the performance of TENGs. In the experiment, TiO2, SiO2, and VO2 LTNC-TENGs are designed and prepared. The results show that under low-energy laser irradiation, the open-circuit voltage (VOC) and short-circuit transferred charge (QSC) increase, primarily due to the enhancement of the surface state energy levels induced by laser irradiation. As the laser energy increases beyond the laser-induced damage threshold (LIDT) of the films, induced damage occurs, generating abundant high-temperature plasma and resulting in decreased VOC and QSC. Building upon these findings, a single-electrode mode LTNC-TENG is developed where voltage jumps occur when laser energy exceeds the film’s LIDT. Furthermore, an electron cloud-potential well model is proposed, describing the approach of atoms from two different materials under laser irradiation without direct contact. This model elucidates the detailed mechanism of laser-induced charge transfer and reveals the “precursor” process of contact electrification. This study contributes to a deeper understanding of the underlying mechanisms of contact electrification and provides a theoretical foundation for the development of more advanced and noncontact TENGs, with largely enhanced lifetime.
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