Photoluminescence Properties of Lanthanide doped Wide Gap Compounds of Interest in Photonics

The subject of this Ph. D. thesis is the characterization of the photoluminescence properties of lanthanide doped wide band gap compounds of interest in photonics and optoelectronics. Wide gap compounds doped with rare earth elements are of great relevance in science and technology, with applications ranging from solid state lasers for industry, medicine and environmental monitoring, to active optical fibers for telecommunication purposes and phosphors displays and lightning applications. Among the materials currently evaluated as host for lanthanide ions, alkaline earth thiogallates are attracting increasing interest due to a number physical and chemical properties that suggest their employment in efficient and low-cost devices. The experimental investigation of the photoluminescence properties of alkaline earth thiogallates doped with lanthanides ions presented in this work, was carried-out characterized by means of time resolved photoluminescence measurements as a function of excitation wavelength and as a function of temperature. Phosphorescence and thermoluminescence properties were also investigated. In particular three main issues of basic research and technological relevance were addressed: the interactions between the rare earth elements and the thiogallate matrix, the interactions between the REE and the defects of the host, the interactions between rare earth elements in codoped samples

Light-Induced Charged and Trap States in Colloidal Nanocrystals Detected by Variable Pulse Rate Photoluminescence Spectroscopy

<p>Intensity instabilities are a common trademark of the photoluminescence of nanoemitters. This general behavior is commonly attributed to random fluctuations of free charges and activation of charge traps reducing the emission yield intermittently. However, the actual physical origin of this phenomenon is actively debated. Here we devise an experiment, variable pulse rate photoluminescence, to control the accumulation of charges and the activation of charge traps. The dynamics of these states is studied, with pulse repetition frequencies from the single-pulse to the megahertz regime, by monitoring photoluminescence spectrograms with picosecond temporal resolution. We find that both photocharging and charge trapping contribute to photoluminescence quenching, and both processes can be reversibly induced by light. Our spectroscopic technique demonstrates that charge accumulation and trap formation are strongly sensitive to the environment, showing different dynamics when nanocrystals are dispersed in solution or deposited as a film.</p>

Charged excitons, Auger recombination and optical gain in CdSe/CdS nanocrystals.

CdSe/CdS colloidal nanocrystals are members of a novel class of light-emitting nanoparticles with remarkable optical properties such as suppressed fluorescence blinking and enhanced emission from multiexciton states. These properties have been linked to the suppression of non-radiative Auger recombination. In this work we employ ultrafast spectroscopy techniques to identify optical signatures of neutral and charged excitonic and multiexcitonic states. We show that Auger recombination of biexcitons is not suppressed, while we observe optical gain and amplified spontaneous emission from multiexciton states and from long-lived charged-exciton states

Acute Delta Hepatitis in Italy spanning three decades (1991–2019): Evidence for the effectiveness of the hepatitis B vaccination campaign

Updated incidence data of acute Delta virus hepatitis (HDV) are lacking worldwide. Our aim was to evaluate incidence of and risk factors for acute HDV in Italy after the introduction of the compulsory vaccination against hepatitis B virus (HBV) in 1991. Data were obtained from the National Surveillance System of acute viral hepatitis (SEIEVA). Independent predictors of HDV were assessed by logistic-regression analysis. The incidence of acute HDV per 1-million population declined from 3.2 cases in 1987 to 0.04 in 2019, parallel to that of acute HBV per 100,000 from 10.0 to 0.39 cases during the same period. The median age of cases increased from 27 years in the decade 1991-1999 to 44 years in the decade 2010-2019 (p &lt; .001). Over the same period, the male/female ratio decreased from 3.8 to 2.1, the proportion of coinfections increased from 55% to 75% (p = .003) and that of HBsAg positive acute hepatitis tested for by IgM anti-HDV linearly decreased from 50.1% to 34.1% (p &lt; .001). People born abroad accounted for 24.6% of cases in 2004-2010 and 32.1% in 2011-2019. In the period 2010-2019, risky sexual behaviour (O.R. 4.2; 95%CI: 1.4-12.8) was the sole independent predictor of acute HDV; conversely intravenous drug use was no longer associated (O.R. 1.25; 95%CI: 0.15-10.22) with this. In conclusion, HBV vaccination was an effective measure to control acute HDV. Intravenous drug use is no longer an efficient mode of HDV spread. Testing for IgM-anti HDV is a grey area requiring alert. Acute HDV in foreigners should be monitored in the years to come

Continuous Measurement of the Temperature of an Industrial Plant Torch

The present invention concerns an apparatus (10) for continuous measurement of the temperature of an industrial plant or refinery torch, comprising an optical coupling system (11), i.e. a system of lenses and/or mirrors and optical fiber cables, and a spectroscopic analyzer, as well as an electronic processor (14), apt to the management of the data acquisition procedures and of the storage and transmission of the same, in connection with said spectroscopic analyser to enable the passage of data. The present invention additionally concerns methods of continuous measurement of the temperature of an industrial plant or refinery torch by means of said apparatus

The temperature dependence of Cr3+:YAG zero-phonon lines

This paper deals with the photoluminescence temperature dependence of the zero-phonon lines of Cr3+ ions in an yttrium aluminium garnet (YAG) matrix. Experimental data were analysed in the framework of electron-phonon coupling in the quadratic approximation and it was found that Cr3+ ions in the YAG matrix are strongly coupled with lattice vibrations, with a Debye temperature of about 550 K and a value of the quadratic coupling constant of 0.65. The analysis of both homogeneous and inhomogeneous contributions to the photoluminescence linewidth is performed and the results obtained are compared with previously reported data for Fe3+:YAG and discussed with respect to the different dependences of the two transition metal ions on the crystal field

Statistical Thermodinamics of Schottky Defects in Metal Nanoparticles

The controversy about the size dependence of the vacancy concentration in metal nanoparticles is here reconsidered in the framework of the statistical thermodynamics. The fractional concentration of vacancies in a spherically shaped metal nanoparticle is calculated by taking into account both the core and the surface defective systems. Notwithstanding the formation energies of core and surface defects are found to increase as the particle size decreases, it is shown that the fractional concentration reaches a maximum at s mall particle sizes, provided that the formation energy of the surface vacancies in macro-crystals is sufficiently smaller than that expected in the bulk. This apparently counterintuitive conclusion, which may reconcile early opposite views, is a mere consequence of the high surface to volume ratio in nanostructures. Numerical calculations performed for copper nanoparticles are presente

A Quantum Adaptation to Roll Truly Random Dice in Role Playing Games

In role-playing games (RPGs), players are called upon to assume the role of a character moving in an imaginary environment and facing several challenges. Their success or failure often depends on randomizers like cards or dice. Regarding the latter, the most commonly used in RPGs are the Platonic solids with the addition of the ten-sided die. They are commonly simulated through classical computers, however, since true randomness is not in their nature, they can only generate pseudorandom numbers. On the contrary, quantum computers exploit the nondeterministic nature of quantum mechanics, so they are perfect candidates for truly random simulations in games of chance. For this reason, this paper proposes and tests various quantum circuits for sampling uniformly distributed discrete values within a fixed range, corresponding to the number of faces of the dice. The simulations reveal the pure randomness of the output of the implemented circuits. They were then used to generate random numbers within a three-dimensional dice-rolling game

Energy transfer in Ce and Eu co-doped barium thiogallate: A photoluminescence characterization

In this work we report for the first time the fluorescence properties of Ce3+ single-doped and Ce3+/Eu2+ co-doped BaGa2S4 crystals, studied by means of time resolved measurements. The single-doped samples fluorescence was characterized by the Ce3+ radiative transitions from the 2D level to the 2F5/2 and 2F7/2 levels with a lifetime of 18 ns, and by a radiative transition from the Eg level to the ground state of Ce3+ ions with a lifetime of 11 ns. The co-doped samples fluorescence was characterized by Eu2+ radiative transition from 4f6d state to the ground state with a lifetime of 290 ns. Ce3+ emissions in co-doped samples are strongly quenched and a lifetime of 6 ns is observed. The reported data are discussed in the framework of energy transfer process between Ce and Eu. The rate of the energy transfer was estimated in 7.5 × 107 s-1 with efficiency of 66%

Donor-acceptor pairs and excitons recombinations in AgGaS2

Silver thiogallate (AgGaS2) is a ternary semiconductor which crystallizes in the chalcopyrite structure. Silver thiogallate has been widely used in different applications for its interesting physical properties: wide transparency range (from 0.5 to 12 mu m), high non-linear optical coefficient combined with good mechanical properties. The direct band gap in this compound is of about 2.7 eV and emissions due to free and bound excitons had been observed. Photoluminescence spectrum is also characterized by a wide emission band centred at 496 nm (2.50 eV) due to donor-acceptor pairs recombination (DAP). We performed photoluminescence (PL) measurements exciting with the third harmonic (3.5 eV) of a Nd:YAG laser from room temperature down to 10 K at different excitation power. In this work, we report the dependence of the photoluminescence features of AgGaS2 On the excitation power at various temperatures: ionization energy of defects are estimated on the basis DAP theoretical model and of thermal quenching of the photoluminescence; evidences of non-radiative processes competitive to DAP is also presented. (c) 2006 Elsevier B.V. All rights reserved