Ultra-weak emission and microcurrents instabilities in blue GaN LEDs at different stages of degradation

It is found that the ultra-weak luminescence observed in microcurrents mode in blue GaN LEDs with multiple quantum wells is due to tunnel-recombination processes with the participation of defect states and local potential wells of various depths, which arise as a result of planar fluctuations of indium in the InGaN layers of the active region. Digital photographs were obtained and patterns of ultra-weak luminescence of the surface of LED crystals were analyzed. It is shown that the patterns of luminescence, along with the current-voltage characteristic, demonstrate significant changes after testing even at the initial stages of degradation, which indicates a high sensitivity of these parameters to degradation processes and the possibility of their use in diagnostic and non-destructive testing methods.

Rapid FRET-based homogeneous immunoassay of procalcitonin using matched carbon dots labels

A novel method for the detection of procalcitonin in a homogeneous system by matched carbon dots (CDs) labeled immunoprobes was proposed based on the principle of FRET and double antibody sandwich method. Blue-emitting carbon dots with a strong fluorescence emission range of 400-550nm and red-emitting carbon dots with the best excitation range of 410-550nm were prepared before they reacted with procalcitonin protoclone antibody pairs to form immunoprobes. According to the principles of FRET, blue-emitting carbon dots were selected as the energy donor and red-emitting carbon dots as the energy receptor. The external light source excitation (310nm) could only cause weak luminescence of CDs. However, once procalcitonin was added, procalcitonin and antibodies would be combined with each other quickly (≤ 20 min). Here, blue-emitting carbon dots acquired energy could be transferred to red-emitting carbon dots efficiently, causing the emitted fluorescence enhancement of red-emitting carbon dots. The fluorescence detection results in PBS buffer solution and diluted rabbit blood serum showed that the fluorescence intensity variation was linear with the concentration of procalcitonin. There was a good linear relationship between F/F0 and procalcitonin concentrations in PBS buffer solution that ranged from 0 to 100ng/ml, and the linear equation was F/F0 = 0.004 * Cpct + 0.98359. Detection in the diluted rabbit serum led to the results that were linear in two concentration ranges, including 0-40ng/ml and 40-100ng/ml, and the detection limit based on 3σ/K was 0.52ng/ml. It’s likely that this matched CDs labeled immunoprobes system can provide a new mode for rapid homogeneous detection of disease markers.

Tuning luminescence of didysprosium single-molecule magnets with π-conjugated/non-conjugated bridging ligand

Here, we reported two didysprosium single-molecule magnets constructed with {Dy(bbpen)(MeOH)} subunits and -conjugated tpb or non-conjugated tpcb bridge. The former exhibits extremely weak luminescence that make it difficult to simulate...

Analysis of Selected Properties of Fruits of Black Chokeberry (Aronia melanocarpa L.) from Organic and Conventional Cultivation

Chokeberry fruits can be treated as very rich sources of bioactive compounds and, therefore, have a very high biological value. The purpose of the study was to compare selected chemical and physical properties of chokeberry fruits, both from organic and conventional cultivations located near Cracow. Chemical composition of the fruit, content of the antioxidant activity, bioactive compounds, and ultra-weak luminescence were analyzed. It was proved that chokeberry fruits are rich in bioactive compounds and that ecological crops produce fruits with a higher level of such compounds. Chokeberry fruits from organic farms were proven to have a higher content of bioactive ingredients and antioxidant activity than in traditionally grown fruits. The total amount of sugars was ambiguous because both the highest and the lowest values were determined in fruits from traditional cultivation. Photon emissivity determined on the basis of ultra-weak luminescence was higher in fruits from organic cultivations. A very high correlation was also found between the photon emissivity and the content of polyphenols as well as the antioxidant activity.

New Perspectives on Photosystem II Reaction Centres

We apply the differential optical spectroscopy techniques of circular polarisation of luminescence (CPL) and magnetic CPL (MCPL) to the study of isolated reaction centres (RCs) of photosystem II (PS II). The data and subsequent analysis provide insights into aspects of the RC chromophore site energies, exciton couplings, and heterogeneities. CPL measurements are able to identify weak luminescence associated with the unbound chlorophyll-a (Chl-a) present in the sample. The overall sign and magnitude of the CPL observed relates well to the circular dichroism (CD) of the sample. Both CD and CPL are reasonably consistent with modelling of the RC exciton structure. The MCPL observed for the free Chl-a luminescence component in the RC samples is also easily understandable, but the MCPL seen near 680nm at 1.8K is anomalous, appearing to have a narrow, strongly negative component. A negative sign is inconsistent with MCPL of (exciton coupled) Qy states of either Chl-a or pheophytin-a (Pheo-a). We propose that this anomaly may arise as a result of the luminescence from a transient excited state species created following photo-induced charge separation within the RC. A comparison of CD spectra and modelling of RC preparations having a different number of pigments suggests that the non-conservative nature of the CD spectra observed is associated with the ‘special pair’ pigments PD1 and PD2.

Tetrabenzo[5.7]Fulvalene: A Forgotten Aggregation Induced-Emission Luminogen

Tetrabenzo[5.7]fulvalene, one of the first recognized stable members of mixed fulvalenes, has attracted widespread interest for its remarkable structure. However, little has been known about its photoactivity, most likely owning to its very weak luminescence in solution state. Here we show for the first time that this compound exhibits aggregation-induced emission (AIE) properties. Its photoluminescence and X-ray crystal structure reveal an interesting mechanism of AIE phenomenon.

Tetrabenzo[5.7]Fulvalene: A Forgotten Aggregation Induced-Emission Luminogen

Tetrabenzo[5.7]fulvalene, one of the first recognized stable members of mixed fulvalenes, has attracted widespread interest for its remarkable structure. However, little has been known about its photoactivity, most likely owning to its very weak luminescence in solution state. Here we show for the first time that this compound exhibits aggregation-induced emission (AIE) properties. Its photoluminescence and X-ray crystal structure reveal an interesting mechanism of AIE phenomenon.

Evaluation of Quality of Eggs from Hens Kept in Caged and Free-Range Systems Using Traditional Methods and Ultra-Weak Luminescence

The paper presents the results of an evaluation of the quality of eggs from laying hens kept in caged and free range systems using traditional methods and ultra-weak luminescence (USL). It was found that the tested eggs were fresh and were characterized by the required quality, as demonstrated by analysis of the egg white and egg yolk. Eggs from free-range laying hens were characterized by an eight-fold higher emission of photons compared to eggs from caged hens, and they had over three times higher content of natural antioxidants in the form of carotenoids. Most probably, the higher number of photons emitted is associated with a higher content of biologically active substances in the material under study. Photon emission also varies in different ways depending on the specific hen breeding system. Differences in time in the identified maximum values of photon emission result from the composition of individual parts of the egg. Different times in which the emission peaks occurred for free-range eggs and for caged eggs were observed. The application of the USL method in order to confirm its usefulness in the assessment of food quality requires further research.

High sensitivity fluorescence up-conversion spectroscopy of 3MLCT emission of metal-organic complexes

We demonstrate the implementation of a broadband fluorescence up-conversion set-up with high signal-to-noise ratio and dynamic range allowing for the detection of weak luminescence from triplet states in Fe(II) NHC complexes. Based on the experimentally determined radiative rates and the emission spectra, these states have dominant MLCT character.