The luminescence spectra of CaWO4, CaMoO4, and ZnWO4 scintillating crystals were investigated in the temperature range 8–400K The excitation photon energy was varied from the ultraviolet (45eV) to the hard x-ray region (35keV) It is found that as the excitation energy decreases the relative intensity of the low-energy luminescence band, attributed to the extrinsic emission of defect centers in CaWO4 and CaMoO4 crystals, increases This observation is interpreted in terms of the total absorption of incident radiation, ie, the variation of the mean penetration depth of the photons with their energy It indicates that the centers responsible for the extrinsic emission in the crystals with scheelite structure are mainly localized in a thin (∼100nm) surface layer On the other hand no noticeable changes with the excitation energy were found in the emission spectra of ZnWO4 crystals with wolframite structure The possible implication of this finding is discussed The light yield of the crystals is compared

Luminescence of CaWO4, CaMoO4, and ZnWO4 scintillating crystals under different excitations

Inorganic scintillators are important elements of a new type of cryogenic phonon scintillation detector (CPSD) being developed for single particle detection. These detectors, exhibiting superior energy resolution and the ability to identify the type of interaction in an event, are considered to be the next generation of instrumentation in the search for extremely rare events. This paper presents the latest results of our research on cryogenic scintillators for CPSD applications in the search for dark matter. The paper gives a description of the concept of direct dark matter detection and the operation principles of CPSD, discusses the major material requirements and summarizes the results of investigations over a wide temperature range of the luminescence and scintillation properties of tungstates (CaWO4 and ZnWO4), molybdates (CaMoO4, MgMoO4 and CdMoO4) and Ti-doped Al2O3.

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Cryogenic scintillators in searches for extremely rare events

Features of the reflectivity spectra in the fundamental absorption region were analysed for a series of tungstates. The contribution of electronic states of cations to the formation of the bottom of the conduction band and the top of the valence band is demonstrated. Its relation with the dominant mechanism of the energy transfer to the emission centres and the nature of these centres is discussed.

Optical and luminescent properties of anisotropic tungstate crystals

The colloidal synthesis of ZnO−WO3 heteroaggregates composed of 3−5 nm particles is presented. These sols can be used to prepare nanocrystalline ZnWO4 xerogels, powders, and thin films with strong blue fluorescence (quantum yield between 25 and 50% at room temperature). The conversion of the precursor aggregates into nano- and microcrystalline monoclinic ZnWO4 Sanmartinite has been followed by XRD, DTA−TG−MS, SEM, FTIR, optical absorption, and fluorescence methods. The ZnWO4 crystallites start to develop at 350 °C, and their mean crystal size increases with temperature to 35 nm at 400 °C and 120 nm at 600 °C. At the same time, the fluorescence intensity increases by 3 orders of magnitude within the aforementioned temperature regime, no matter whether X-rays or UV photons are used to excite the samples. In complementary time-resolved X-ray fluorescence investigations, two recombination processes in the micro- and millisecond range were detected. In weakly fluorescing ZnO−WO3 aggregate samples at sizes betw...

Conversion of Colloidal ZnO-WO3 Heteroaggregates into Strongly Blue Luminescing ZnWO4 Xerogels and Films

ZnWO4 nanoparticles (NPs) that are assembled and aggregated together as chain-like morphology have been synthesized via the reaction of Zn(II) salt solution with sodium tungstate in the presence of the DNA scaffold under 5 min of microwave heating. The reaction parameters have been tuned to control the size of the individual particles and diameter of the chains. The significance of different reaction parameters and specific growth mechanism for the formation of particles is elaborated. The DNA-ZnWO4 nanoassemblies have been used in two potential applications for the first time, namely, supercapacitor and catalysis studies. Supercapacitor study revealed that DNA-ZnWO4 nanoassemblies exhibited good electrochemical properties having high specific capacitance value ∼72 F/g at 5 mV s–1, and electrodes possessed a good cyclic stability with more than 1000 consecutive times of cycling. Catalysis studies have been done for benzyl alcohol oxidation, and it was observed that DNA-ZnWO4 nanoassemblies having smaller ...

Bio-molecule assisted aggregation of ZnWO4 nanoparticles (NPs) into chain-like assemblies: material for high performance supercapacitor and as catalyst for benzyl alcohol oxidation

The spectra of luminescence and photoexcitation as well as emission decay kinetics in various parts of spectra are investigated in ZnWO4 and CdWO4 crystals in a wide temperature range (4.2 to 300 K). The bands of red afterglow and of rapidly decaying violet luminescence are observed for the first time. The likeness of the emission properties of ZnWO4 and CdWO4 allows the explanation of the luminescence in these tungstenite type crystals in terms of configurational coordinate diagrams of self-activated radiation centre and of self-trapped exciton.



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Luminescence of ZnWO4 and CdWO4 Crystals

In the era of wireless technologies, orthogonal frequency division multiplexing (OFDM) techniques and their modifications gained huge popularity. Despite all their benefits they still have several Achilles' heels. One of them is the negative influence of a narrowband or continuous wave (CW) electromagnetic disturbance (EMD). In this paper, a specific CW EMD removal algorithm for OFDM communication systems was investigated for its stability when both a CW EMD and additive white Gaussian noise (AWGN) were affecting the OFDM communication system. By using the spectral leakage phenomenon, the algorithm estimates a mismatch between the sub carriers and CW EMD frequencies and subsequently calculates all the needed CW parameters, i.e. amplitude and phase. The goal of the investigation was to find out which modulation scheme gives the best algorithm's performance. Therefore after a number of simulations on the algorithm with different power variations of CW EMD and AWGN, the results turned out to be better when lower order modulation schemes were in use. These results were explained in the frequency domain as the AWGN's fraction with regard to the CW EMD error was minimum within the subcarriers close to the CW EMD's frequency bin and much higher for other subcarriers. In the end, prepositions on how to maximise the CW removal algorithm's performance under simultaneous CW EMD and AWGN were outlined.

Influence of AWGN on the Possibility to Remove a Continuous Wave EM Disturbance in OFDM systems

This paper presents a study on the electromagnetic robustness of IO-link Wireless and SmartMesh IP for their use on an agricultural vehicle. Especially the multipath fading due to the reflective nature of the agricultural vehicle is challenging for such wireless communication protocols. The electromagnetic robustness was tested in a double reverberation chamber as well as on an actual combine harvester. Detailed test setups and procedures are in the paper. Throughout the tests, several key parameters related to the quality of service (QoS) of both protocols were monitored with a specific focus on latency and packet error rate (PER). Test results show that both IO-link Wireless and SmartMesh IP experience a decrease in data throughput and an increase in latency in a (semi-)reverberant environment. In particular, transmission power needs to be carefully regulated for IOLW, while SmartMesh IP is dependent on the mesh formation and the distance between its Manager and Motes. Test results also show that a fully reverberant environment is harsher than the actual harvester. Thus, the initial steps were made to dampen the RC with absorbers to comply with the environment created in a harvester, resulting in a comparable PER of 4.1 %.

A. E. Ovechkin

Papers

Luminescence of ZnWO4 and CdWO4 Crystals

Influence of AWGN on the Possibility to Remove a Continuous Wave EM Disturbance in OFDM systems

A Study of Electromagnetic Robustness of IO-Link Wireless and SmartMesh IP for Applications on an Agricultural Vehicle