Increase In Photoluminescence Lifetime Research Articles

Effect of surface modification on the photoluminescent properties of γ-Ga2O3 nanocrystals

Ga2O3 nanocrystals with compelling optical properties attract broad attention from the scientific and industrial community. However, the influence of surface modification on the photoluminescent properties of Ga2O3 NCs remains unexplored. Here, we report comparative investigations of the photoluminescent properties of oleylamine-capped and ligand-free γ-Ga2O3 nanocrystals. The removal of oleylamine ligand on the Ga2O3 nanocrystal surface via a post-synthesis reaction is accompanied by the accumulation of positive surface charges and a reduction of oxygen vacancies. The change of nanocrystal surface leads to an appreciable red shift of emission spectrum along with a substantial increase in photoluminescence lifetime. Modeling the photoluminescence decay dynamics of Ga2O3 nanocrystals indicate the change of photoluminescent property is correlated to the decrease of the number density of donors and donor Bohr radius resulting from the change of nanocrystal surface.

Moisture-dependent room-temperature perovskite crystallization in vacuum flash-assisted solution processed intermediate phase films

We propose a straightforward intermediate-phase strategy to facilitate large-area crystallization of perovskite under room-temperature: preparing intermediate phase film with vacuum flash-assisted solution processing (VASP) method and performing controlled moisture-exposure subsequently. Moisture molecules penetrate into the whole intermediate film, remove residual solvent molecules, and trigger room-temperature crystallization of perovskite in a wide humidity range (25–80% RH), while negligible hydroxyl species are observed in the intermediate phase and resultant perovskite films. Without antisolvent, thermal-annealing and additive, high-humidity (80% RH) exposure of intermediate-phase film under room-temperature results in crystalline perovskite with a 8× increase in grain size and a 6× increase in photoluminescence lifetime, which is attributed to the homogenous and stable intermediate phase prepared by VASP and the synergistic effect of H 2 O and residual solvent molecules. Without antisolvent, thermal-annealing and additive, high-humidity (80% RH) exposure of intermediate-phase precursor film under room-temperature results in crystalline perovskite with a 8× increase in grain size and a 6× increase in photoluminescence lifetime. • The intermediate phase strategy applies in the wide range of 25–80% RH humidity. • Moisture exposure under room-temperature induces identical chemical transition. • Negligible hydroxyl species are observed in perovskite and its intermediate. • 80% RH exposure leads micron-size grains and microsecond fluorescence lifetime.

Mechanistic understanding of the charge carrier trapping in CsPbCl3 perovskite nanocrystals

The optical properties of CsPbCl3 perovskite nanocrystals (NCs) with varied sizes were studied in the temperature range from 80 to 320 K by steady-state and time-resolved photoluminescence (PL) spectroscopy. The CsPbCl3 NCs were synthesized with a hot-injection approach at reaction temperature of 140–180 °C. The PL emissions in NC films originate from localized excitons. It is found that NC films shows a significant decrease in PL intensity with increasing temperature while they exhibit a clear increase in PL lifetime from 80 K to around 250 K and then a reduction at high temperature. The abnormal temperature dependence of PL lifetimes in NC films is related to thermal activation of trapped carriers in the NCs. The change of average lifetimes with emission energy indicates the thermal degradation result from the loss of ligands on the surface of NC films. Moreover, the PL intensities, peak energies, and bandwidths of the NC films as a function of temperature are discussed detail.

Substantially enhanced photoelectrochemical performance of TiO2 nanorods/CdS nanocrystals heterojunction photoanode decorated with MoS2 nanosheets

Two-dimensional (2D) MoS2 nanosheets (NSs) modified 1D TiO2 nanorods/0D CdS nanocrystals (NCs) heterojunction has been fabricated by all solution process as a potential anode for photoelectrochemical (PEC) water splitting applications. This heterojunction photoanode shows high photocurrent density of 3.25 mA/cm2 at 0.9 V vs. RHE (0 V vs. Ag/AgCl) compared to the pristine TiO2/CdS photoanode. The influence of MoS2 NSs on PEC performance of TiO2/CdS/MoS2 heterojunction has been systematically investigated. We demonstrate that MoS2 NSs transfer holes from CdS and facilitate further charge separation in TiO2/CdS. Time resolved photoluminescence measurement reveals increase in photoluminescence lifetime due to the presence of MoS2 NSs in TiO2/CdS/MoS2 resulting in enhanced PEC activity. This work suggests that 1D TiO2/0D CdS/2D MoS2 heterojunction prototype is an interesting system where MoS2 NSs can be utilized to improve charge separation in photoanodes. This study would pave the way towards designing new heterojunction functional materials for efficient PEC applications.

Methylammonium Chloride Induces Intermediate Phase Stabilization for Efficient Perovskite Solar Cells

Summary One of the most effective methods to achieve high-performance perovskite solar cells has been to include additives that serve as dopants, crystallization agents, or passivate defect sites. Cl-based additives are among the most prevalent in literature, yet their exact role is still uncertain. In this work, we systematically study the function of methylammonium chloride (MACl) additive in formamidinium lead iodide (FAPbI3)-based perovskite. Using density functional theory, we provide a theoretical framework for understanding the interaction of MACl with a perovskite. We show that MACl successfully induces an intermediate to the pure FAPbI3 α-phase without annealing. The formation energy is related to the amount of incorporated MACl. By tuning the incorporation of MACl, the perovskite film quality can be significantly improved, exhibiting a 6× increase in grain size, a 3× increase in phase crystallinity, and a 4.3× increase in photoluminescence lifetime. The optimized solar cells achieved a certified efficiency of 23.48%.

Highly Efficient Perovskite Solar Cells via Nickel Passivation

AbstractToday's state‐of‐the‐art perovskite solar cells (PSCs) are utilizing polycrystalline perovskite thin films via solution‐processing at low temperature (<150 °C). It is extremely significant to enlarge grain size and passivate trap states for perovskite thin films to achieve high power conversion efficiency. Herein, a strategy for defect passivation of perovskite films via metal ion Ni2+ is for the first time reported. It is found that addition of Ni2+ can significantly generate polyporous PbI2 films due to a different solubility between NiCl2 and PbI2 which benefits penetration of MAI and thus formation of large grain perovskite films eventually. It further demonstrated that Ni2+ ions can effectively passivate PbI3− antisite defects and restrain the generation of Pb0 by interacting with the under‐coordinated halide anions and halide‐rich antisites. Therefore, introducing moderate Ni2+ ions result in a significant increase in photoluminescence lifetime from 285 to 732 ns. Accordingly, a power conversion efficiency of 20.61% can be achieved for the 3% Ni2+ addition‐based PSCs with an enhanced cell stability under ambient conditions. This work provides a promising route toward perovskite films featuring with high crystallinity and low trap‐density.

Correlation of quantum efficiency and photoluminescence lifetime of ZnO tetrapods grown at different temperatures

Absolute external quantum efficiencies (ηs) and photoluminescence (PL) decay lifetimes of ZnO tetrapods grown at different temperatures were measured. All the tetrapods had an UV peak at about 390 nm and a very weak defect emission. Measurements showed that the tetrapods have ηs of 2%-4% at room temperature. The sample, grown at optimal temperature, exhibited the largest absolute η of 4.3% and longest PL decay lifetimes among all the samples. These results showed that precise control of growth temperature plays an important role in making high quality ZnO tetrapods. In time-resolved measurement, the PL decay time constant (τ) versus temperature is well fitted by the theoretical prediction τ=a T32. This increase in PL lifetime with increasing temperature shows that the excited state relaxation is dominated by radiative recombination.

Phosphorescent Sensor for Biological Mobile Zinc

A new phosphorescent zinc sensor (ZIrF) was constructed, based on an Ir(III) complex bearing two 2-(2,4-difluorophenyl)pyridine (dfppy) cyclometalating ligands and a neutral 1,10-phenanthroline (phen) ligand. A zinc-specific di(2-picolyl)amine (DPA) receptor was introduced at the 4-position of the phen ligand via a methylene linker. The cationic Ir(III) complex exhibited dual phosphorescence bands in CH(3)CN solutions originating from blue and yellow emission of the dfppy and phen ligands, respectively. Zinc coordination selectively enhanced the latter, affording a phosphorescence ratiometric response. Electrochemical techniques, quantum chemical calculations, and steady-state and femtosecond spectroscopy were employed to establish a photophysical mechanism for this phosphorescence response. The studies revealed that zinc coordination perturbs nonemissive processes of photoinduced electron transfer and intraligand charge-transfer transition occurring between DPA and phen. ZIrF can detect zinc ions in a reversible and selective manner in buffered solution (pH 7.0, 25 mM PIPES) with K(d) = 11 nM and pK(a) = 4.16. Enhanced signal-to-noise ratios were achieved by time-gated acquisition of long-lived phosphorescence signals. The sensor was applied to image biological free zinc ions in live A549 cells by confocal laser scanning microscopy. A fluorescence lifetime imaging microscope detected an increase in photoluminescence lifetime for zinc-treated A549 cells as compared to controls. ZIrF is the first successful phosphorescent sensor that detects zinc ions in biological samples.

Aqueous Synthesis of Zinc Blende CdTe/CdS Magic-Core/Thick-Shell Tetrahedral-Shaped Nanocrystals with Emission Tunable to Near-Infrared

We demonstrate the synthesis of near-IR-emitting zinc blende CdTe/CdS tetrahedral-shaped nanocrystals with a magic-sized (approximately 0.8 nm radius) CdTe core and a thick CdS shell (up to 5 nm). These high-quality water-soluble nanocrystals were obtained by a simple but reliable aqueous method at low temperature. During the growth of the shell over the magic core, the core/shell nanocrystals change from type I to type II, as revealed by their enormous photoluminescence (PL) emission peak shift (from 480 to 820 nm) and significant increase in PL lifetime (from approximately 1 to approximately 245 ns). These thick-shell nanocrystals have a high PL quantum yield, high photostability, compact size (hydrodynamic diameter less than 11.0 nm), and reduced blinking behavior. The magic-core/thick-shell nanocrystals may represent an important step toward the synthesis and application of next-generation colloidal nanocrystals from solar cell conversion to intracellular imaging.

Optical doping of soda-lime-silicate glass with erbium by ion implantation

Soda-lime-silicate glass has been implanted with 500 keV Er ions at fluences between 8.6×1014 and 1.8×1016/cm2 with the aim to optically dope the material in the near surface region. The ion range was 100 nm, and Er concentrations in the range 0.09—1.9 at. % were obtained. The characteristic photoluminescence (PL) of Er3+ around 1.54 μm is observed at room temperature in as-implanted glass. The PL intensity increases by an order of magnitude after annealing above 500 °C, as a result of annihilation of implantation-induced defects. Annealing causes an increase in PL lifetime. As a function of Er fluence, the PL intensity first increases, but levels off above ∼6×1015 Er/cm2 (0.6 at. % Er peak concentration). The PL lifetime decreases from 13 to 1.5 ms for increasing Er concentration. The decrease in PL efficiency with concentration is attributed to concentration quenching caused by Er-Er interactions. The optimal combination of PL intensity and lifetime is reached at ≊0.4 at. % peak concentration, for which the lifetime is 6 ms. For high Er concentrations and high pump intensities (∼3 kW/cm2) an additional, intensity dependent quenching mechanism (possibly cooperative upconversion) is observed.