Photoluminescence enhancement study in a Bi-doped Cs2AgInCl6 double perovskite by pressure and temperature-dependent self-trapped exciton emission.

Here, we report a halide precursor acid precipitation method to synthesize Cs2AgIn1-xBixCl6 (x = 0, 0.02, 0.04, 0.08, 0.16, 0.32, 0.64, and 1) microcrystals. Cs2AgInCl6 and Bi derivative double perovskites show broadband white light emission via self-trapped excitons (STEs) and have achieved the highest internal quantum efficiency of up to 52.4% at x = 0.08. Synchrotron X-ray diffraction confirmed the linear increase of lattice parameters and cell volume with Bi3+ substitution at In3+ sites. Absorbance, photocurrent excitation, and photoluminescence excitation spectra are used to observe possible transitions from the valence to the conduction band or free exciton (FE) states as well as transitions within local Bi3+ states. The broadband photoluminescence is quenched via a single nonradiative process with an activation energy ΔE = 1490 cm-1 for Cs2AgIn0.92Bi0.08Cl6. Under normal conditions, we observed STE emission, but applying external pressure alters the electronic structure such that at elevated pressure, the only emission via the FE state is observed. We anticipate that structure, temperature and pressure-dependent photoluminescence studies will help the future use of a single-source lead-free double perovskite for white light-emitting diode applications.

Structural, optical and magnetic properties of Y3-0.02-xEr0.02Yb x Al5O12 (0 < x < 0.20) nanocrystals: effect of Yb content.

The paramagnetic Y3-0.02-x Er0.02Yb x Al5O12 (x = 0.02, 0.06, 0.10, 0.12, 0.18, 0.20) nanocrystals (NCs) were synthesized by the microwave-induced solution combustion method. The XRD, TEM and SEM techniques were applied to determine the NCs' structures and sizes. The XRD patterns confirmed that the NCs have for the most part a regular structure of the Y3Al5O12 (YAG) phase. The changes of the distance between donor Yb3+ (sensitizer) and acceptor Er3+ (activator) were realized by changing the donor's concentration with a constant amount of acceptor. Under 980 nm excitation, at room temperature, the NCs exhibited strong red emission near 660 and 675 nm, and green upconversion emission at 550 nm, corresponding to the intra 4f transitions of Er3+ (4F9/2, 2H11/2, 4S3/2) â†’ Er3+ (4I15/2). The strongest emission was observed in a sample containing 18% Yb3+ ions. The red and green emission intensities are respectively about 5 and 12 times higher as compared to NCs doped with 2% of Yb3+. In order to prove that the main factor responsible for the increase of the upconversion luminescence efficiency is reduction of the distance between Yb3+ and Er3+, we examined, for the first time the influence of hydrostatic pressure on luminescence and luminescence decay time of the radiative transitions inside donor ion. The decrease of both luminescence intensity and luminescence decay times, with increasing hydrostatic pressure was observed. After applying hydrostatic pressure to samples with e.g. 2% and 6% Yb3+, the distance between the donor and acceptor decreases. However, for higher concentrations of the donor, this distance is smaller, and this leads to the effective energy transfer to Er3+ ions. With increasing pressure, the maximum intensity of near infrared emission is observed at 1029, 1038 and 1047 nm, what corresponds to 2F5/2 â†’ 2F7/2 transition of Yb3+.

Surface Plasmon-Coupled Emission of Rhodamine 110 Aggregates in a Silica Nanolayer.

First analysis of strong directional surface plasmon-coupled emission (SPCE) of ground-state formed intermolecular aggregates of Rhodamine 110 (R110) in silica nanofilms deposited on silver nanolayers is reported. Until now, the processes of energy transport and its trapping due to aggregate formation have not been studied in the presence of SPCE. A new approach to multicomponent systems with weakly and strongly fluorescent centers making use of fluorophore-surface plasmon interaction is presented. The analysis is based on comparison of experimental free-space emission spectra (F-SE), experimental SPCE with theoretical surface plasmon resonance spectra (SPR). It is shown that, due to the dispersion of SPCE, the detection of weak aggregate emission is straightforward if only the monomers and aggregates fluorescence spectra are somewhat spectrally shifted. SPCE studies confirmed the formation of weakly fluorescent higher order aggregates of R110 in silica films. The results indicate that the increase of energy transfer from monomers to aggregates is due to fluorophore-plasmon interaction.

Surface-plasmon-coupled emission of Rhodamine 110 in a silica nanolayer.

The first observation of strong directional surface-plasmon-coupled emission (SPCE) of Rhodamine 110 in silica nanofilms deposited on silver nanolayers is reported. The preparation of the material is described in detail. The intensity of SPCE exceeds 10 times that of free space fluorescence and total linear light polarization in the SPCE ring is observed. A new experimental setup and an original data collection method is presented. Our material completely preserves its fluorescence properties for at least eight months.

Photodynamic therapy with 5-aminolevulinic acid and diamino acid derivatives of protoporphyrin IX reduces papillomas in mice without eliminating transformation into squamous cell carcinoma of the skin.

Photodynamic therapy (PDT) is used to treat malignant and nonmalignant diseases. It is also used for cosmetological skin treatment. PDT is generally considered to have a low risk of carcinogenicity. However, instances of nonmalignant human tumors turning malignant have been linked to PDT. In this study, we used 5-aminolevulinic (ALA) acid and 3 water soluble photosensitizers-PP(Arg)(2), PP(Ser)(2)Arg(2), PP(Ala)(2)Arg(2), all diamino acid derivatives of protoporphyrin IX-to treat benign papillomas in FVB/N mice induced by 7,12-dimethylbenz(a)anthracene (DMBA)-12-O-tetradecanoyl-phorbol-13-acetate (TPA). Of these drugs, ALA and PP(Arg)(2) were found the most efficient. PDT reduced the number of papillomas, but with increasing effectiveness of the drugs, the risk of malignant transformation of the papillomas into squamous cell carcinomas increased. The underlying mechanisms are not clear and further investigations are needed.

Acousto-optic interaction with the use of cylindrical ultrasonic waves in the laser cavity.

In this paper, acousto-optic interaction between laser light and cylindrical airborne ultrasound in both He-Ne laser and argon-ion laser cavities is considered. The modulation properties of these acousto-optic systems were studied. The schlieren technique has been used to visualize a cylindrical ultrasonic wave generated in the air by radial vibration of a cylindrical piezoelectric shell. It was revealed that acoustic nonlinear effects together with acoustic absorption appear in the vicinity of the axis, where the ultrasound is focused. The observed waveforms of ultrasonic wave correspond to the curves of modulation of laser light.

Acousto-optic interaction of a Gaussian laser beam with an ultrasonic wave of cylindrical symmetry.

We present experimental studies of the interaction between a narrow Gaussian laser beam and a standing cylindrical ultrasonic wave. As a theoretical approach, a Fourier-optics-based successive diffraction model is used. Depending on the ratio of the Gaussian laser beam diameter to the first nodal diameter of the cylindrical ultrasound, light refraction or diffraction is observed. We experimentally investigate the time-averaged light intensity as well as the modulation of light in the far field of light refraction-diffraction by a cylindrical ultrasound. It is revealed that significant focusing appears if the phase front of the incident light is curved. The focusing effects of the acousto-optic system depend on the width of the laser beam and curvature of the phase front. Finally, possible applications are discussed.