Kinds Of Luminescence Research Articles

Arduino-based light source used to demonstrate mixing of colors and as a simple system for luminescence observations

Additive light mixing can be hard to describe without a proper example. We describe a simple, portable device for demonstration purposes. Its advantage is the use of a RGB diode, which can generate light of variable wavelengths. It may be used to demonstrate principles of color mixing and light penetrating through a tissue, also different kinds of luminescence. Our custom-designed box is 3D printable, allowing for easy reproduction or modification and can be powered by portable power source.

Transient demonstration of exciton behaviours in solid state cathodoluminescence under different driving voltage

In the solid state cathodoluminescence (SSCL), organic materials were excited by hot electrons accelerated in silicon oxide (SiO2) layer under alternating current (AC). In this paper exciton behaviours were analysed by using transient spectra under different driving voltages. The threshold voltages of SSCL and exciton ionization were obtained from the transient spectra. The recombination radiation occurred when the driving voltage went beyond the threshold voltage of exciton ionization. From the transient spectrum of two kinds of luminescence (exciton emission and recombination radiation), it was demonstrated that recombination radiation should benefit from the exciton ionization.

Coherent Nature of the Radiation Emitted in Delayed Luminescence of Leaves

After exposure to light, a living system emits a photon signal of characteristic shape. The signal has a small decay region and a long tail region. The flux of photons in the decay region changes by 2 to 3 orders of magnitude, but remains almost constant in the tail region. The decaying part is attributed to delayed luminescence and the constant part to ultra-weak luminescence. Biophoton emission is the common name given to both kinds of luminescence, and photons emitted are called biophotons. The decay character of the biophoton signal is not exponential, which is suggestive of a coherent signal. We sought to establish the coherent nature by measuring the conditional probability of zero photon detection in a small interval Δ. Our measurements establish the coherent nature of biophotons emitted by different leaves at various temperatures in the range 15–50°C. Our set up could measure the conditional probability for Δ≤100 μs in only 100 ms, which enabled us to make its measurement in the decaying part of the signal. Various measurements were repeated 2000 times in contiguous intervals, which determined the dependence of the conditional probability on signal strength. The observed conditional probabilities at different signal strengths are in agreement with the predictions for coherent photons. The agreement is impressive at the discriminatory range, 0.1–5 counts per Δ, of signal strengths. The predictions for coherent and thermal photons differ substantially in this range. We used the values of Δ in the range, 10 μs–10 ms for obtaining a discriminatory signal strength in different regions of a decaying signal. These measurements establish the coherent nature of photons in all regions of a biophoton signal from 10 ms to 5 hr. We have checked the efficacy of out method by measuring the conditional probability of zero-photon detection in the radiation of a light emitting diode along with a leaf for Δ in the range 10 μs–100 μs. The conditional probability in the diode radiation was different from the prediction for coherent photons when the signal strength was less than 2.5 counts per Δ. Only the diode radiation exhibited photon bunching at signal strength around 0.05 count in Δ.

Self-trapped exciton and recombination luminescence in PbCl 2, PbBr 2 and their mixed crystals

Intrinsic luminescence of PbCl 2, PbBr 2 and their mixture have been investigated at low temperature. Two kinds of luminescence are observed in the pure crystals. The one is excited only in the excitonic absorption band and appears at 3.78 eV (UV) in PbCl 2 and at 2.75 eV (B) in PbBr 2. The other is excited only in the band-to-band region and is located at 2.62 eV (BG) in both crystals. In the PbCl 2(1− x) -PbBr 2 x mixed crystals, two additional bands appear at 3.20 eV ( V 1: x < 0.1) and at 2.95 eV ( V 2: 0.01 < x < 0.5) owing to the coexistence of Cl − and Br −. It is proposed that there are two types of self-trapped excitons (STE): the [Pb +(X −) 3+ hole] STE responsible for the UV−( X= Cl), B−( X= Br) and V 1 − , V 2 − ( X= Cl, Br) emission, and the [(Pb 2) 3++hole] STE responsible for the BG-emission.

The Kinetics of Excitonic Luminescence in Mixed Silver Halides

ABSTRACTTwo kinds of luminescence (excitonic luminescence and excitonic molecule luminescence) were investigated for solid solutions AgBr1-xClx after pulsed electron beam and N2 laser irradiation. Careful theoretical treatment of a set of experimental excitonic luminescence kinetics is presented. It is shown that the effective activation energy of Agoi migration is a linear function of the composition x. The narrow peak of the excitonic molecule luminescence shifts from 2.66ev in pure AgBr towards higher energies as x increases.

Simultaneous detection of native and luminol-dependent luminescence of stimulated human polymorphonuclear leukocytes

A method for investigating the cellular response of polymorphonuclear leukocytes to various stimuli was introduced using simultaneously native (luminol-independent) and luminol dependent luminescence as an indicator for myeloperoxidase (MPO)-H2O2-halide and O2- mediated reactions. In experimental systems containing low concentrations of luminol the total light emission was separated into contributions of native and luminol-dependent luminescence by making use of the different spectral behaviour of the two kinds of luminescence. Consequently the MPO-H2O2-halide system could be distinguished from the O2- dependent system by interpreting the recorded temporal traces of the emitted light.

On mechanism of recombination luminescence of alkali-halides doped by Eu2+

It is known that the ions of Eu2+ enter the lattice of alkali-halides together with the cation vacancies. The complex Eu2+Vc- is stable up to 200°C. It, at the same time, is the center of emission. We have found out that there is an electronic recombination mechanism of the luminescence upon the stimulation with light from F- or electronic activator bands in alkali-halides doped by Eu2+. Besides we have stated that there is a mechanism of emission like that mentioned above in X-ray induced and thermostimulated luminescence. The activator emission which is characteristic of Eu2+ is observed in all kinds of luminescence. Special test result is that Eu3+ is not produced under X-ray irradiation, hence the activator must form the hole recombination centers which are needed for the production of the electronic recombination mechanism of the luminescence. The study of the spectral characteristics of the investigated crystals indicates that the hole activator centers are produced under X-ray irradiation. These centers are observed in the induced absorption spectra in KI-Eu. If such centers are not observed in the crystal, photostimulated and thermostimulated luminescence does not take place.