CH3NH3PbI3 perovskite layered films deposited on substrates with and without a titania support structure have been prepared and studied using time-resolved femtosecond transient absorption (fs-TA) spectroscopy in the visible light range (450-800 nm). The electron injection dynamics from the photoexcited perovskite layers to the neighboring film structures could be directly monitored via the transient bleaching dynamics of the perovskite at ∼750 nm and thus systematically studied as a function of the layer-by-layer architecture. In addition, for the first time we could spectrally distinguish transient bleaching at ∼750 nm from laser-induced fluorescence that occurs red-shifted at ∼780 nm. We show that an additional bleach feature at ∼510 nm appears when PbI2 is present in the perovskite film. The amplitudes of the PbI2 and perovskite TA peaks were compared to estimate relative amounts of PbI2 in the samples. Kinetic analysis reveals that perovskite films with less PbI2 show faster relaxation rates than those containing more PbI2. These fast dynamics are attributed to charge carrier trapping at perovskite grain boundaries, and the slower dynamics in samples containing PbI2 are due to a passivation effect, in line with other recently reported work.

Perovskite films were prepared using single step solution deposition at different annealing temperatures and annealing times. The crystal structure, phases and grain size were investigated with XRD, XPS and SEM/EDX. The prepared films show a typical orientation of tetragonal perovskite phase and a gradual transition at room temperature from the yellow intermediate phase to the black perovskite phase. Films with high purity were obtained by sintering at 100 °C. In addition, the chemical composition and crystal structure of intermediate phase were investigated in detail. FTIR, UV-vis and NMR spectra revealed the occurance of DMF complexes. Interestingly, the intermediate phase could be transformed to the black perovskite phase upon X-ray irradiation. In addition, the recovery of the aged perovskite films from a yellow intermediate phase back to the black perovskite was shown to be viable via heating and X-ray irradiation.

Prostate cancer is one of the most common cancers and among the leading causes of cancer deaths in the United States. Men diagnosed with the disease typically undergo radical prostatectomy, which often results in incontinence and impotence. Recurrence of the disease is often experienced by most patients with incomplete prostatectomy during surgery. Hence, the development of a technique that will enable surgeons to achieve a more precise prostatectomy remains an open challenge. In this contribution, we report a theranostic agent (AuNP-5kPEG-PSMA-1-Pc4) based on prostate-specific membrane antigen (PSMA-1)-targeted gold nanoparticles (AuNPs) loaded with a fluorescent photodynamic therapy (PDT) drug, Pc4. The fabricated nanoparticles are well-characterized by spectroscopic and imaging techniques and are found to be stable over a wide range of solvents, buffers, and media. In vitro cellular uptake experiments demonstrated significantly higher nanoparticle uptake in PSMA-positive PC3pip cells than in PSMA-negative PC3flu cells. Further, more complete cell killing was observed in Pc3pip than in PC3flu cells upon exposure to light at different doses, demonstrating active targeting followed by Pc4 delivery. Likewise, in vivo studies showed remission on PSMA-expressing tumors 14 days post-PDT. Atomic absorption spectroscopy revealed that targeted AuNPs accumulate 4-fold higher in PC3pip than in PC3flu tumors. The nanoparticle system described herein is envisioned to provide surgical guidance for prostate tumor resection and therapeutic intervention when surgery is insufficient.

Iridium(iii) complexes bearing the 2-(2-quinolinyl)quinoxaline ligand absorb weakly at 450–750 nm and can be used as broadband reverse saturable absorbers.

Near-infrared emitting AgInS2/ZnS nanocrystals were synthesized by carefully controlling the growth conditions in a Ag/In/Zn/S solution with less zinc relative to the other precursors. The role of having a smaller amount of zinc (8 atom %) was systematically investigated in an effort to understand the mechanism of the largely red-shifted emission. The AgInS2/ZnS nanocrystals can be transferred to aqueous solutions while retaining the emission intensity. The near-infrared emission and solubility in aqueous solutions make AgInS2/ZnS nanocrystals excellent candidates for bioimaging and photocatalytic applications.

Fluorescent carbon dots were synthesized from milk by microwave cooking and used for two-photon excitedin vitrocell imaging.

In this work, the spatially dependent recombination kinetics of mixed-halide hybrid perovskite CHNHPb(BrCl ) (0 ≤ x ≤ 0.19) single crystals are investigated using time-resolved photoluminescence spectroscopy with one- and two-photon femtosecond laser excitation. The introduction of chloride by substituting a fraction of the bromide leads to a decreased lattice constant compared to pure bromide perovskite ( x = 0) and a higher concentration of surface defects. The measured kinetics under one-photon excitation (1PE) shows that increasing the chloride addition quenches the photoluminescence (PL) lifetimes, due to substitution-induced surface defects. In stark contrast, upon 2PE, the PL lifetimes measured deeper in the bulk become longer with increasing chloride addition, until the halide substitution reaches the critical concentration of ∼19%. At x = 19% Cl concentration, a significant reversal of this behavior is observed indicating a change in crystal structure beyond the continuous trends observed at lower percentages of halide substitution ( x ≤ 11%). The observed opposing trends, based on 1PE versus 2PE, highlight a dichotomy between extrinsic (surface) and intrinsic (bulk) effects of chloride substitution on the carrier dynamics in lead bromide perovskites. We discuss the physical relation between halide exchange and bulk carrier lifetimes in CHNHPbBr in terms of the Rashba effect. We propose that the latter is suppressed at the surface due to disorder in the alignment of the MA and that it increases in the bulk with Cl concentration because of the reduction in lattice parameters, which compresses the space available for the MA orientational degrees of freedom.

This work presents a novel method for preparing perovskite films using a simple processing technique. Perovskite paste was prepared by dispersing an equimolar mix of PbI 2 and methyl ammonium iodide powders into terpineol with stirring. From these precursors, perovskite films were fabricated using doctor blading and drying for 24 h at room temperature. The prepared films were then placed into relative humidity (RH) levels of 30, 50, and 70 % to test the moisture stability. The crystal structure, phases, and morphology were investigated with XRD and SEM/EDX. These samples exhibited good stability against long time exposure to moisture for 70 days. The XRD results showed that samples stored at RH 70 % contained only a small amount of hydrate compound after 70 days storage, while in the sample stored at RH 50 %, the formation of PbI 2 was observed. The sample at RH 30 % manifested almost no change when stored for the same storage period. We attribute the enhanced moisture stability, compared with the spin-coated samples, to a passivated surface of the perovskite film by terpineol which exhibits a hydrophobic moiety. Time-resolved photoluminescence measurements show that the passivation of surface defect states by the formation of either PbI 2 or hydrated compound leads to prolonged charge carrier recombination times.Graphical Abstract