Nonlinear-optical refraction of silver nanoparticle composites

In this paper, the experimental data on nonlinear refraction of silver nanoparticle composites using a standard Z-scan technique are presented. It was found that the colloids of silver nanoparticles of various size possess a defocusing ability. Based on general considerations, one can conclude thermal lens nature of the nonlinear refraction of the colloids. Significantly different magnitudes of the nonlinear refractive index of silver nanoparticles suspended in water and in glycerol can be explained by differences in the specific heat capacity of mentioned fluids. The effective thickness for nonlinear-optical interaction of light with a two-dimensional silver nanoparticle array was estimated

Megahertz non-contact luminescence decay time cryothermometry by means of ultrafast PbI2 scintillator

Realtime in situ temperature monitoring in difficult experimental conditions or inaccessible environments is critical for many applications. Non-contact luminescence decay time thermometry is often the method of choice for such applications due to a favorable combination of sensitivity, accuracy and robustness. In this work, we demonstrate the feasibility of an ultrafast PbI2 scintillator for temperature determination, using the time structure of X-ray radiation, produced by a synchrotron. The decay kinetics of the scintillations was measured over the 8–107 K temperature range using monochromatic pulsed X-ray excitation. It is found that lead iodide exhibits a very fast and intense scintillation response due to excitons and donor-acceptor pairs, with the fast decay component varying between 0.08 and 0.5 ns – a feature that can be readily exploited for temperature monitoring. The observed temperature dependence of the decay time is discussed in terms of two possible mechanisms of thermal quenching – transition over activation barrier and phonon-assisted escape. It is concluded that the latter provides a better fit to the experimental results and is consistent with the model of luminescence processes in PbI2. We evaluated the sensitivity and estimated the accuracy of the temperature determination as ca. ±6 K at 107 K, improving to ±1.4 K at 8 K. The results of this study prove the feasibility of temperature monitoring, using ultrafast scintillation of PbI2 excited by X-ray pulses from a synchrotron, thus enabling non-contact in-situ cryothermometry with megahertz sampling rate

Optical Properties of LiNbO₃-Ag Nanocomposites

The article presents the experimental results of the investigation of the absorption spectra and nonlinear refraction of the metal-dielectric nanocomposite that contains the lithium niobate pyroelectric crystal coated with the silver nanofilms on its surface. The atomic force microscopy surface research of these crystals with and without films are also provided. The nanowidth silver films impact on optical spectra and nonlinear refraction of LiNbO₃-Ag nanocomposite was analyzed depending on the sign of the side charge of the crystal, that contain nanofilms

Scintillation properties and X-ray luminescence spectra of zinc telluride at cryogenic temperatures

The paper is devoted to the study of X-ray luminescence spectra, the scintillation light output and the decay time characterisation of undoped ZnTe at low temperatures down to 6 K. Also, the photoconductivity spectrum in a visible region has been investigated. Due to significant thermal quenching, the scintillations at α-particle excitation were detected in the sample only below T = 150 K. The emission of the crystal is attributed to the radioactive recombination of the holes trapped by Zn vacancies and electrons captured at the shallow levels of impurities or defects. The scintillation efficiency increased with further cooling. It has been found that at α-particle excitation undoped ZnTe exhibits a fairly competitive light output equal to 117 ± 20% of CaWO4reference scintillator. This finding underpins potential applications of ZnTe as a scintillation detector in the cryogenic experiments, particularly for the cryogenic search for neutrinoless double beta decay of130Te. It has been also found that ZnTe will be attractive as a conventional scintillation detector at the temperature of liquid nitrogen (T = 77 K). At this temperature, the scintillator exhibits a reasonably short decay time and a sufficient scintillation response to particle excitation. A practical implementation of this idea poses no real technical challenge since photomultipliers and Si-based photodetectors are proven to operate reliably and efficiently at this temperature

Scintillation properties and X-ray luminescence spectra of zinc telluride at cryogenic temperatures

The paper is devoted to the study of X-ray luminescence spectra, the scintillation light output and the decay time characterisation of undoped ZnTe at low temperatures down to 6 K. Also, the photoconductivity spectrum in a visible region has been investigated. Due to significant thermal quenching, the scintillations at α-particle excitation were detected in the sample only below T = 150 K. The emission of the crystal is attributed to the radioactive recombination of the holes trapped by Zn vacancies and electrons captured at the shallow levels of impurities or defects. The scintillation efficiency increased with further cooling. It has been found that at α-particle excitation undoped ZnTe exhibits a fairly competitive light output equal to 117 ± 20% of CaWO4reference scintillator. This finding underpins potential applications of ZnTe as a scintillation detector in the cryogenic experiments, particularly for the cryogenic search for neutrinoless double beta decay of130Te. It has been also found that ZnTe will be attractive as a conventional scintillation detector at the temperature of liquid nitrogen (T = 77 K). At this temperature, the scintillator exhibits a reasonably short decay time and a sufficient scintillation response to particle excitation. A practical implementation of this idea poses no real technical challenge since photomultipliers and Si-based photodetectors are proven to operate reliably and efficiently at this temperature

Formation of PbMnI2_2 alloys: Structural, photoluminescence and nuclear quadrupole resonance studies

The structural, optical and nuclear quadrupole resonance (NQR) measurements of PbMnI$_2$ alloys were carried out. This allows us to study the peculiarities of the formation of such alloys. It was found that pure PbI$_2$ and Pb$_{1-X}$Mn$_X$I$_2$ crystals with X = (0.03–0.05) have the phase of 2H-polytype. It was shown that the investigated alloys can be presented as the crystal regions of Pb$_{1-X}$Mn$_X$I$_2$ solid solutions, embedded in PbI$_2$ crystal matrix. These formations can be considered as platelet-shaped nanoparticles with a surface of several microns and a thickness of several tens of nm. Thus, PbMnI$_2$ alloys are heterogeneous PbI$_2$–PbMnI$_2$ nanocomposites. The results of NQR spectra measurements also show that Mn$^{2+}$ ions preferably replace Pb$^{2+}$ ions in the crystalline layers. Here, the local deformations occur because the radii of Pb$^{2+}$ and Mn$^{2+}$ ions differ significantly. The broadening of optical and NQR lines is due to the presence of both these deformations and the crystal field fluctuations, which are characteristic of semiconductor solid solutions