Suzuki Phase Research Articles

Improved Lithium Iodide neutron scintillator with Eu[formula omitted] activation II: Activator zoning and concentration effects in Bridgman-grown crystals

We have previously reported on the formation of Suzuki Phase precipitate particles as a result of the addition of the divalent activator ion Eu 2+ to the monovalent alkali halide host LiI. [Boatner et al. (2017)]. These precipitates form during Bridgman or other melt-growth processes, even at low Eu2+ concentrations (e.g., 0.1% EuI2 doping), and scatter the scintillation light reducing the optical transparency of the scintillator and adversely affecting its radiation-detection performance. In our prior work, we developed a two-stage thermal-treatment method for the post-growth removal of the Suzuki Phase particles and the realization of a significant improvement in the optical transparency and associated neutron-detection of LiI:Eu2+ scintillators. These improvements resulted in neutron-detection performance that is superior to GS-20 glass and that allows for the application of pulse height gamma-ray discrimination over a wide range of gamma ray energies as opposed to pulse shape discrimination. Here, we apply the two-stage thermal-processing method for the removal of Suzuki phase precipitates and carry out an in-depth study, first, of the neutron scintillator performance versus the Eu2+ activator-ion-concentration spatial variation as a result of zoning effects during the Bridgman growth of LiI:Eu2+ and, second, of the effects of varying the initial Eu2+ activator ion concentration prior to crystal growth. The Eu2+ zoning variation results allow one to identify and select the most efficient location of the scintillation performance in a directionally solidified single-crystal boule. The present study of the initial activator concentration levels shows that there are, in fact, two distinct types of luminescence centers with varying performance properties — one that occurs only at low EuI2 addition levels (e.g., 0.01 to 0.06 %EuI2) and that is quickly replaced by a second luminescing center with increasing Eu2+ content (e.g., at ∼0.1% EuI2). The light yield for the luminescing center formed using a Eu activator in LiI is a critical function of the Eu concentration in the range of 0.01 to 0.1 % EuI2, and a high light yield of 100,000 photons/neutron is observed at the 0.06 %EuI2additive level prior to thermal processing.

Improved lithium iodide neutron scintillator with Eu2+ activation: The elimination of Suzuki-Phase precipitates

Monovalent alkali halides such as NaI, CsI, and LiI are widely used as inorganic scintillators for radiation detection due to their light yield, the capability for the growth of large single crystals, relatively low cost, and other favorable characteristics. These materials are frequently activated through the addition of small amounts (e.g., a few hundred ppm) of elements such as thallium - or sodium in the case of CsI. The monovalent alkali halide scintillators can also be activated with low concentrations of Eu2+, however Eu activation has previously not been widely employed due to the non-uniform segregation of the divalent Eu dopant that leads to the formation of unwanted phases during Bridgman or other solidification crystal-growth methods. Specifically, for Eu concentrations near and above ~0.5%, Suzuki Phase precipitates form in the course of the melt-growth process, and these Suzuki Phase particles scatter the scintillation light. This adversely affects the scintillator performance via reduction in the optical transmission of the material, and depending on the crystal thickness and precipitated-particle concentration, this reduction can occur up to the point of opacity. Here we describe a post-growth process for the removal of Suzuki Phase precipitates from single crystals of the neutron scintillator LiI activated with Eu2+ at concentrations up to and in excess of 3wt%, and we correlate the resulting neutron-detection performance with the thermal processing methods used to remove the Suzuki Phase particles. The resulting improved scintillator properties using increased Eu activator levels are applicable to neutron imaging and active interrogation systems, and pulse-height gamma-ray spectroscopy rather than pulse-shape discrimination can be used to discriminate between gamma ray and neutron interaction events.

Fano resonance-based highly sensitive, compact temperature sensor on thin film lithium niobate.

In this Letter, we report a Fano resonance-based highly sensitive and compact temperature sensor fabricated on thin film lithium niobate (TFLN) Suzuki phase lattice (SPL) photonic crystal. The experimental sensitivity is estimated to be 0.77 nm/°C with a photonic crystal size of only 25 μm × 24 μm. This sensitivity is 38 times larger than the intrinsic one of lithium niobate which is 0.02 nm/°C. The demonstrated sharp and high extinction ratio characteristics of the Fano lineshape resonance could be an excellent candidate in developing a high sensitivity temperature sensor, electric field sensor, etc.

Study of NaCl:Mn2+ nanostructures in the Suzuki phase by optical spectroscopy and atomic force microscopy

NaCl:Mn2+ nanostructures in the Suzuki phase have been studied by fluorescence (emission and excitation) spectroscopy and atomic force microscopy (AFM) as a function of temperature. The “as-grown” samples give rise to two broad emission bands that peak at 508 (green emission) and 610nm (red emission). The excitation spectrum shows peaks at 227nm and 232nm for emission wavelengths at 508nm and 610nm, respectively. When the samples are heated continuously from room temperature up to 220°C, the green emission (associated to the excitation peak at 227nm) disappears at a temperature close to 120°C, whilst only the red emission remains, which is characteristic of manganese ions. AFM images on the (001) surface (freshly cleaved) show several conformations of nanostructures, such as disks of 20–50nm in diameter. Particularly, the images also reveal nanostructures with rectangular shape of ~280×160nm2 and ~6nm height; these are present only in samples with green emission associated to the Suzuki phase. Then, the evidence suggests that this topographic configuration might be related to the interaction with the first neighbors and the next neighbors, according to the configuration that has been suggested for the Suzuki phase.

Formation of Structured Nanophases in Halide Crystals

When halide crystals KCl and NaCl are slightly doped by PbCl 2, (in orders of 10−4 mol / mol ) the structurally stable nanophases (“quantum dots”) are formed via nucleation within the bulks of their matrices. Using lattice modeling we have found in KCl–Pb system natural nucleation pathway from single impurity–vacancy complex to Suzuki phase, not demonstrated in previous analyses; further transition to PbCl 2 is difficult due to high stability of this phase. In the case of NaCl–Pb, no stable “end point” of aggregation was observed and our calculations suggest nucleation may readily proceed to large PbCl 2 clusters when initially formed platelike cluster reaches a certain critical thickness. These results coincide with our experimental data.

Formation of structured nanophases in halide crystals

When halide crystals KCl and NaCl are slightly doped by PbCl(2), (in orders of 10(-4) mol/mol) the structurally stable nanophases ("quantum dots") are formed via nucleation within the bulks of their matrices. Using lattice modeling we have found in KCl-Pb system natural nucleation pathway from single impurity-vacancy complex to Suzuki phase, not demonstrated in previous analyses; further transition to PbCl(2) is difficult due to high stability of this phase. In the case of NaCl-Pb, no stable "end point" of aggregation was observed and our calculations suggest nucleation may readily proceed to large PbCl(2) clusters when initially formed platelike cluster reaches a certain critical thickness. These results coincide with our experimental data.

ChemInform Abstract: Structure and Properties of NaCl and the Suzuki Phase Na6CdCl8

ChemInform Abstract: Structure and Properties of NaCl and the Suzuki Phase Na6CdCl8

Thermal dissolution of Eu2+ Suzuki phase nanostructures in KBr crystals monitored by pulsed photoacoustic and photoluminescence techniques

Abstract Suzuki-type precipitated phases are nanostructures that change the optical and mechanical properties of the crystal in which they have been formed. The dissolution process of the Europium Suzuki phase (SP) nanostructures was induced by continuous heating (1 °C/min) of KBr:Eu 2+ single crystals and it was simultaneously monitored by two techniques: photoacoustic (PA) and photoluminescence (PL). Each sample was heated from room temperature to 205 °C; meanwhile a focused laser pulse (355 nm) impinged on one crystal face to excite the low energy Europium absorption band and generate the photoacoustic signal. The correlation coefficients between subsequent PA signals were used to build a thermal profile and its behaviour was found to be directly related with the absorption coefficient of Eu 2+ ion in its crystalline environment. From correlation analysis and Fourier fast transform (FFT) applied to the PA signal data, the dynamical thermal dissolution process has been studied and compared with simultaneous emission spectrum data obtained by the PL technique. The results show good agreement with the literature.

Studies of the thermal dissolution process of the Suzuki phase of theEu2+ ion in KBr single crystals by analysis of photoacoustic signals

An experimental investigation of the thermal behaviour of thedissolution process of the Suzuki phase (SP) by continuous heating(1 °C min−1)of KBr:Eu2+ crystals is reported in this work. The thermal profiles were determined by the correlation functionsbetween subsequent photoacoustic (PA) signals registered during the dissolution process.The behaviour of the thermal profile is directly related to the absorption coefficient of theEu2+ ion in precipitated states that are present in the crystal. The PA signal is detected as a consequenceof the non-radiative processes that take place after the excitation of the low-energy band of theEu2+ ion by means of a focused laser pulse at 355 nm. The results obtained bythis method are compared with those simultaneously obtained by thephotoluminescence (PL) technique. The samples were heated from room temperature to205 °C.The PA signal and PL spectrum were obtained every6 °C.The temperature range of the SP dissolution process was from 77 to115 °C.These results are in agreement with those obtained by the PL technique and with the datareported in the literature.

STE LUMINESCENCE FROM THE SUPERSTRUCTURE PHASE Na6CdCl8 IN NaCl:Cd2+ CRYSTALS

Optical Absorption and luminescence studies have been conducted in Nacl crystals contining various amounts of CdCl 2 in order to investigate the electronic excited states and their lattice relaxation processes in Suzuki superstructure lattice. X-ray diffraction measurements have been also made to confirm the presence of the Suzuki phase and to determine its detailed structure. Two broad absorption structures are observed in the energy region of 4.25-5.0 eV (LE) and of 5.0-6.0 eV (HE). With excitation in the LE region, three emission bands are produced at 2.64 (BG), 3.14 (V) and 3.56(UV1)eV. They are attribute to the Cd 2+ impurity-related centers. In case of excitation in the HE region, two prominent emission bands are observed at 2.76 (B) and 2.08 (Y) eV. Taking into consideration the experimental results of X-ray diffraction, thermal treatment and Cd 2+ concentration dependence, the B- and Y-emission are connected to the STE in Suzuki lattice of small and large sizes, respectively.

Suzuki phase in two-dimensional sonic crystals

In analogy with the structures discovered by Suzuki in alkali halides, in this article we introduce a twodimensional acoustic system consisting of a periodic distribution of impurities ~vacancies! in a host array. A triangular lattice of cylindrical sound scatterers is chosen as the host. The sonic crystal, called the Suzuki phase, shows extraordinary sound transmission properties: it holds the attenuation bands of the host structure and it also presents additional ones associated to the periodicity of the missing cylinders. The experiments agree with predictions based on the calculated acoustic band structure and they are explained by an analysis of eigenstates.

Structure and Properties of NaCl and the Suzuki Phase Na6CdCl8

Ab initio band structure calculations based on density functional theory were performed for NaCl, CdCl2, and the Suzuki phase Na6CdCl8. For Na6CdCl8 the structural parameters and physical properties, such as molar volume and the magnitude of the free internal coordinate and electric field gradients, together with their pressure dependence, were obtained. These results are compared to calculations for NaCl and CdCl2 to investigate the hypothesis that Na6CdCl8 can only exist as precipitates in a stabilizing surrounding NaCl matrix. From the present calculations it follows that the lattice parameters of NaCl and the Suzuki phase are identical within the accuracy of the calculations, and that therefore no “clamping” of the Suzuki phase occurs. However, it is found that Na6CdCl8 is only metastable with respect to the decomposition into solid sodium chloride and cadmium chloride. Calculations for NaCl were also used to evaluate the quality of different exchange-correlation functionals (LDA, GGA-PW91, GGA-PBE96)...

Lead emission from the cadmium Suzuki phase in NaCl:CdCl2:Pb2+

The system NaCl:CdCl2:Pb2+ has been studied by the photoluminescence technique. The results for quenched crystals consist of the usual emission bands of Pb2+ in a NaCl matrix: at room temperature, one intense band centred at 314 nm; at liquid-nitrogen temperature, two bands, one peaking at 312 nm and one weak band at 380 nm. The aging of these crystals at 355 K produces a cadmium Suzuki phase precipitate in which the minor impurity Pb2+ ions are incorporated. The emission of these incorporated lead ions into the Suzuki phase consist of two emission bands. These are centred at 388 and 460 nm; the latter is very intense even at room temperature. The temperature behaviour of these bands suggests that the former can be assigned to the AX band, while the latter to the AT emission band. This might be the result of a large coupling to the T2g vibrational modes of the Cd2+ Suzuki phase. In crystals annealed at higher temperatures the cadmium ions precipitate into the CdCl2 phase. For this case the lead emission consists of the usual high-energy AT band (390 nm) and the low-energy AX band (458 nm).

Energy Transfer in the Thermally Annealed KCI: Pb2+, Mn2+ System

physica status solidi (b)Volume 171, Issue 2 p. 517-521 Original Paper Energy Transfer in the Thermally Annealed KCI: Pb2+, Mn2+ System R. Cywiński, R. Cywiński Institute for Low-Temperuture und Structure Research, Polish Acudemy of Sciences, Wroclaw Search for more papers by this authorS. Bicliardi, S. Bicliardi Dipartmento di Fisica dell'Università di Purma , Gruppo Nuzionale di Struttura dellu Muteria del Consiglio Nuzionale delle RicercheSearch for more papers by this authorM. Manfredi, M. Manfredi Dipartmento di Fisica dell'Università di Purma , Gruppo Nuzionale di Struttura dellu Muteria del Consiglio Nuzionale delle RicercheSearch for more papers by this author R. Cywiński, R. Cywiński Institute for Low-Temperuture und Structure Research, Polish Acudemy of Sciences, Wroclaw Search for more papers by this authorS. Bicliardi, S. Bicliardi Dipartmento di Fisica dell'Università di Purma , Gruppo Nuzionale di Struttura dellu Muteria del Consiglio Nuzionale delle RicercheSearch for more papers by this authorM. Manfredi, M. Manfredi Dipartmento di Fisica dell'Università di Purma , Gruppo Nuzionale di Struttura dellu Muteria del Consiglio Nuzionale delle RicercheSearch for more papers by this author First published: 1 June 1992 https://doi.org/10.1002/pssb.2221710223Citations: 1 P.O. Box 937, PL-50-950 Wroclaw, Poland. Viale delle Scienze, 1-43 100 Parma, Italy. AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Citing Literature Volume171, Issue21 June 1992Pages 517-521 RelatedInformation

Structure and interaction of impurity-vacancy (Mg2+-Vc-) dipoles in crystalline LiF

Both the spatial and electronic structure of Mg2+, Vc- and (Mg2+-Vc-)n centres (n=1, 4) in a LiF crystal have been calculated by semiempirical techniques of pair potentials and INDO. Crystal polarization was taken into account in a self-consistent way in terms of the Mott-Littleton approach. It is shown that a consistent choice of parametrization of both methods gives rather close values for displacements of ions surrounding the centres under study. The Mg2+ compensation by a cation vacancy located in its nearest surrounding along the (110) axis is found to be most energetically favourable. It is shown that the aggregation of impurity-vacancy dipoles can lead to the formation of a phase with a periodical structure differing from the traditional Suzuki phase.

On the Energy Transfer in the Thermally Annealed KCl: Pb2+, Eu2+ System

AbstractPb → Eu energy transfer mechanisms in the thermally annealed KCl: Pb2+, Eu2+ system are examined by means of optical absorption, emission, and time decay spectra of the luminescence. The thermal annealing produced the formation of the Pb2+ Suzuki phase and the results show that the Eu2+ ions enter this phase by substituting for some Pb2+ ions. The Pb → Eu transfer is found to be a very efficient process, with a very short transfer time. The analysis of the time decay signals shows that the transfer is a single pair mechanism; no migration of the excitation energy is experimentally detected.

Precipitation-induced quenching of Eu2+ luminescence in potassium halides.

The effect of the ${\mathrm{Eu}}^{2+}$ precipitation state on the luminescence and decay time of europium-doped potassium halides has been systematically investigated. Each type of Eu precipitate is well characterized by a distinct lifetime. Nucleation of Eu${\mathit{X}}_{2}$-type precipitates (X=Cl, Br, or I) strongly reduces the lifetime of ${\mathrm{Eu}}^{2+}$ as compared to the lifetime of quenched samples (which is on the order of 1 \ensuremath{\mu}s). This reduction can be explained by a concentration quenching of emitted light in these types of precipitates. On the other hand, nucleation of the other type of Eu precipitates (which have been previously tentatively associated with Suzuki phase structures) does not produce this quenching of light, and only a slight increase in their lifetime value, due to the new environment, is now observed.

Characterization of the aggregated phase in KCl:Cd2+and KCl:Mn2+by Raman spectroscopy

Abstract The aggregated phase of the impurities in the systems KCl:Cd2+ and KCl:Mn2+ has been identified as the Suzuki phase by Raman spectroscopy. The linear increase in the integrated scattering intensities of the Raman lines with concentration of the impurities may be attributed to an increase in the mean precipitate size of the Suzuki phase.

Optical and EPR study of precipitated phases in NaBr:Mn2+

As-grown NaBr:Mn2+ crystals have been investigated using photostimulated luminescence, EPR and optical absorption techniques in the 6 K-300 K temperature range. Through them the formation of a precipitated phase involving Mn2+, whose magnetic phase transition temperature is well below 6 K, is established. This conclusion then supports the presence of the Suzuki phase previously inferred from Raman data. The value Omega * (A1g)=130+or-7 cm-1 derived at 14 K from the vibrational progression in the 4T1(G) band concurs with the corresponding Raman value. It is shown that, only through the 4A1(G), 4E(G) peak, lying at 419.6 nm at 14 K for the present case, the presence of MnBr64- cannot be definitely established. This situation is however improved by looking at the Stokes shifts, the 10 Dq values and also the optical bandwidths. The analysis of 10 Dq and Omega (A1g) suggests that the Mn2+-Br- distance R is higher than for MnBr2 or Cd0.85Mn0.15Br2. However, an increase Delta R=4.8 pm with respect to MnBr2 does not fully account for the 'anomalous' 4A1(G), 4E(G) peak position in the present case where a value J=0.014 cm-1 has been derived for the exchange constant from the EPR bandwidth Delta Hpp=117 G. Attention has been paid to the influence of temperature changes on the optical peak positions as well as to the effects of a quenching at 600 degrees C. Although Delta Hpp becomes 2.5 times higher, no evidence is obtained on the formation of isolated Mn2+ ions after quenching.

Pb2+-->Mn

The analysis of optical emission and excitation spectra of KBr single crystals doubly doped with ${\mathrm{Pb}}^{2+}$ and ${\mathrm{Mn}}^{2+}$ ions has been accomplished for different sample conditions. The results show that highly efficient nonradiative energy transfer occurs from ${\mathrm{Pb}}^{2+}$ to ${\mathrm{Mn}}^{2+}$ ions which then decay by giving orange-red (640 nm) emission. A comparison of excitation spectra for manganese emission of as-grown and annealed samples shows that ${\mathrm{Mn}}^{2+}$ excitation is associated with the aggregated phase of ${\mathrm{Pb}}^{2+}$ ions. The 640-nm emission has been explained on the basis of a model which proposes trapping of ${\mathrm{Mn}}^{2+}$ ions in the Suzuki phase of ${\mathrm{Pb}}^{2+}$ dipoles. The electron-paramagnetic-resonance results also support this model. The results for annealed and subsequently aged samples are further in conformity with the model. Finally, the observed 520-nm emission band in as-grown samples has been attributed to a Suzuki-type aggregated phase of ${\mathrm{Mn}}^{2+}$ ions.