Scintillation and dosimeter properties of <Superscript>6</Superscript>LiF/CaF<Subscript>2</Subscript>:Eu eutectic composites

We investigated scintillation and dosimeter properties of ⁶LiF/CaF₂ eutectic composites doped with different concentrations of Eu (0.005, 0.02, 0.1, 0.3, and 1.0). In the photoluminescence (PL) and scintillation spectra, an emission peak at 430 nm due to the 5d–4f transitions of Eu²⁺ was observed. The intensity of PL and scintillation for ⁶LiF/CaF₂:0.005%Eu was the highest among the samples tested. In thermally stimulated luminescence (TSL), several glow peaks of ⁶LiF/CaF₂:0.005%Eu were observed after X-ray irradiation of 1000 mGy. The TSL response exhibited a linear response against X-ray dose over a dose range of 1–10,000 mGy. In optically stimulated luminescence (OSL), an emission peak was observed at 430 nm during a stimulation by 630 nm light after X-ray irradiation of 1000 mGy. The OSL intensity was the highest for ⁶LiF/CaF₂:0.005%Eu among all the samples investigated.     

Thermally stimulated luminescence studies in combustion synthesized polycrystalline aluminum oxide

Synthesis of materials by combustion technique results in homogeneous and fine crystalline product. Further, the technique became more popular since it not only saved time and energy but also was easy to process. Aluminum oxide phosphor was synthesized by using urea as fuel in combustion reaction. Photoluminescence (PL) and thermally stimulated luminescence (TSL) characteristics of γ-irradiated aluminum oxide samples were studied. A broad PL emission with a peak at ∼ 465 nm and a pair of strong and sharp emissions with peaks at 679 and 695 nm were observed in γ-rayed samples. The PL intensity was observed to increase with increase in γ-ray dose. Two prominent and well resolved TSL glows with peaks at 210°C and 365°C were observed in all γ-irradiated Al₂O₃ samples. The TSL intensity was also found to increase with increase in γ-ray dose. The TSL glow curves indicated second order kinetics.     

Thermally stimulated luminescence and photoluminescence investigations of Eu3+ and Eu2+ doped SrBPO5

Thermally stimulated luminescence (TSL) investigations of SrBPO₅:Eu^3?+ and SrBPO₅:Eu^2?+ phosphors were carried out in the temperature range of 300–650 K. In order to characterize the phosphors, X-ray diffraction and photoluminescence (PL) techniques were used. The emission spectrum of air heated SrBPO₅:Eu^3?+ phosphor exhibited emission bands at 590, 614, 651 and 702 nm under 248 nm excitation, assigned to transitions of Eu^3?+ ion. In phosphor prepared in reducing (Ar + 8% H₂) atmosphere, a broad emission band due to Eu^2?+ ranging from 350 to 400 nm was observed with 340 nm excitation. EPR studies have confirmed the presence of Eu^2?+ ions in the samples prepared in reducing atmosphere. TSL glow curve of SrBPO₅:Eu^3?+ had shown intense peaks around 397, 510, 547 K and a weak peak around 440 K whereas in case of SrBPO₅:Eu^2?+ system, glow peaks at 414, 478 and weak peak at 516 nm were observed. The shift in TSL glow pattern can be attributed to stabilization of different oxidation states of the dopant ion in the host lattice. Apart from this, TSL trap parameters such as trap depth and frequency factor were determined. Spectral characteristics of TSL emission have shown that Eu^3?+?/Eu^2?+ ion acts as the luminescent centre in the respective phosphors.     

Ionizing radiation induced luminescence properties of Mn-doped LiCa(Al,Ga)F<Subscript>6</Subscript>

Optical, scintillation and dosimeter properties of Mn 0.3 and 10 mol% doped LiCaAlF₆ and Mn 10 % doped LiCaAl_0.9Ga_0.1F₆ crystals were studied. Mn²⁺ emission appeared around 520 nm in the photoluminescence, scintillation and optically stimulated luminescence (OSL). As a dosimeter, the OSL and thermally stimulated luminescence (TSL) dose response functions were evaluated, and both the OSL and TSL showed a good linearity between the irradiated X-ray dose and response signal intensity from 1 to 1000 mGy. Compared with previously reported Ce- or Eu-doped LiCaAlF₆, OSL properties were improved.     

Microstructure and electrical properties of MgO-doped SnO2 varistor ceramics

The effect of MgO addition on the properties of (Co, Nb, Cr)-doped SnO₂ varistors was investigated. The samples with different MgO concentrations were fabricated by the conventional ceramic method and sintered at 1,250, 1,300, 1,350 and 1,400 °C for 2 h. It was found that the nonlinear coefficient presented a peak value of 28 and lowest leakage current density of 7 μA/cm² when 0.5 mol% MgO was added. The breakdown electrical field increased from 174 to 531 V/mm with increasing MgO from 0.0 to 2.0 mol%. The relative dielectric constant decreased with increasing MgO from 0.0 to 0.5 mol%, but increased with more MgO added. The dielectric loss decreased obviously in the case of low frequency with MgO added, and it had the lowest value when 0.5 mol% MgO added. The optimal samples were obtained by doping MgO with 0.5 mol% and sintering at 1,350 °C.     

Influence of substrate temperature on ultraviolet emission of ZnO films prepared by ultrasonic spray pyrolysis

ZnO films were deposited on MgO substrates (ZnO/MgO) by ultrasonic spray pyrolysis. Substrate temperature varied from 200 to 350°C. The crystallographic properties and surface morphologies of the ZnO/MgO films were studied by X-ray diffraction and scanning electron microscopy. The properties of photoluminescence (PL) for the films were investigated by dependence of PL spectra on the substrate temperature and the ambient temperature. Ultraviolet (UV) emission peak (3.37 eV) was dominantly detected at 18 K, which sustained at 300 K with a reduced value of the peak energy. The ZnO/MgO films prepared at 350°C showed the strongest UV emission peak at 18 and 300 K among the films in this study.     

Preparation,spectroscopic properties and enhanced luminescence of Tb<Superscript>3+</Superscript>-doped LuAG phosphors and transparent ceramics by introduction of Sc<Superscript>3+</Superscript>

Tb-doped LuAG(lutetium aluminum garnet) and LuSAG(lutetium scandium-aluminum garnet) precursors were synthesized through a co-precipitation process, using ammonium hydrogen carbonate as precipitator. Single-phase cubic LuAG/Tb and LuSAG/Tb phosphors were obtained after calcination at 1000 and 1200 °C, respectively. These powders could be easily sintered into corresponding transparent LuAG/Tb and LuSAG/Tb ceramics in H₂ atmosphere at 1850 °C. The PL excitation and emission spectra were recorded for both phosphors and ceramics. Emission spectra of all materials were found to be typical for Tb³⁺, resulting from radiative relaxation of D level. Both the Tb-doped LuSAG phosphors and ceramics show higher efficient luminescence than LuAG , especially the transparent Tb-doped LuSAG ceramic shows about 150% higher luminescence intensity than transparent Tb-doped LuAG ceramic.     

Annealing effects on structural and optical properties of ZnMgO films grown by RF magnetron sputtering

Two sets of ZnMgO thin films have been fabricated on Si (111) substrates by RF magnetron sputtering, and were annealed at air atmosphere afterwards. The effects of annealing temperature and time on structural and optical properties were also characterized by X-ray diffraction, scanning electron microscopy and photoluminescence (PL) spectra. For samples fabricated at a lower temperature (200 °C, defined as samples I), the experimental results revealed that only hexagonal phase was observed for the films annealed at the temperature range from 180 to 420 °C, and the best crystal quality for the films was found at 240 °C. For samples synthesized at 220 °C (defined as samples II), the crystal structures exhibited anneal-time dependent. The experimental results revealed coexistence of hexagonal and cubic phase when they were annealed at a set temperature of 220 °C with the different annealing time, and the best one can be observed when the anneal time was 30 min. PL spectra showed blue shift for UV peak with the increase of annealing temperature for samples I, and the UV emission occurred red shift and then blue shift when the anneal time increased from 20 to 30 min for samples II.     

Preparation,dosimetric characterisation and investigation of related TSL defect centres in Li3Po4:Mg,Cu phosphor

L3PO4:Mg,Cu, a low effective atomic number and high sensitivity TSL phosphor, has been prepared. Its TSL glow curve shows a major peak around 360 degrees C with minor peaks around 110 degrees C and 230 degrees C. The optimum concentrations of the dopants are found to be 200 ppm each. Its gamma sensitivity is 1.2 times as compared to CaSO4:Dy (0.1 mol%). The optimum preirradiation annealing treatment is found to be 650 degrees C, 15 min. Its PL emission shows a band at 370 nm with excitation band at 250 nm. Dose to TSL response shows that its response is linear up to the gamma dose of 100 Gy for irradiations carried out at RT. An irradiated sample shows a distinct new ESR signal, which is tentatively assigned to an electron/hole localised on one of the oxygen(s) of the phosphate group. Step annealing experiments show decay of the defect centre around 340 degrees C. This correlates well with the TSL peak around 360 degrees C.     

Effects of Li2O3–B2O3–SiO2 addition on dielectric properties and microstructure of MgO–TiO2–ZnO–CaO ceramics

The effect of Li₂O₃–B₂O₃–SiO₂ (LBS) liquid-phase additives on the sintering, microstructures, and dielectric properties of MgO–TiO₂–ZnO–CaO (MTZC) ceramics was investigated. It was found that the sintering temperature could be lowered easily, and the dielectric properties of MTZC ceramics could be greatly improved by adding a small amount of LBS solution additives. With the addition of 10 wt% LBS, the ceramics sintered at 900 °C showed favorable dielectric properties with ε_r = 21.7, Qf = 5.0 × 10⁴ GHz, and TCF = ?21.6 ppm/ °C. The distructive physical analysis showed an excellent co-firing interfacial behavior between the MTZC ceramic and the Ag electrode. It indicated that MTZC ceramics with LBS solution additives have a number of potential applications on passive integrated devices based on the low-temperature co-fired ceramics technology.     

Effects of annealing and deposition temperature on the structural and optical properties of AZO thin films

Al-doped ZnO (AZO) thin films were deposited on p- type Si(100) substrate by r.f magnetron sputtering at 200, 300 and 400 °C substrate temperatures. The deposited films were annealed in air atmosphere for 1 h at temperatures of 700, 800 and 900 °C. The deposition temperature and post-deposition annealing effects on structural and optical properties of the AZO samples were analyzed using X-ray diffraction, atomic force microscope and photoluminescence (PL). After annealing, the value of full width half maximum of the diffraction peaks was decreased as well as, the intensity of visible and strong UV PL emission peaks were increased with temperature. However, the deep-level emission related with zinc point defects was removed by annealing of the samples. Results revealed that all of the as-deposited and annealed AZO films have hexagonal structure along (002) direction and their crystallinity were improved with the increased deposition and post-growth annealing temperatures. In addition, the surface roughness and the particle size of the films were increased with increased deposition and annealing temperatures.     

Thermoluminescence and lyoluminescence in γ-ray irradiated and Ce3+-doped YCa4O(BO3)3 phosphors

YCa₄O(BO₃)₃ crystal having various concentration of Ce ions were synthesized by solid-state diffusion technique. XRD pattern of the sample confirmed the formation of the sample. Thermoluminescence (TL) and lyoluminescence (LL) of the γ-ray-irradiated sample were recorded. Two distinct peaks around 160 and 277 °C were observed in TL glow curves. TL intensity increased with increasing dopant concentration up to 2 mol%. A single sharp peak was observed in the LL glow curve of the sample. It was found that both TL and LL increased almost linearly with γ-ray doses up to 1.5 kGy. Photoluminescence (PL) of the sample was recorded to find the role of rare earth ion doped in YCa₄O(BO₃)₃. PL emission spectrum showed two peaks lying very close to each other around 390 nm which are characteristics of 5d → 4f transition of Ce³⁺ ions. When LL of samples was recorded after removing the TL peaks it did not show any emission. This indicates that emission centres responsible for TL are also responsible for LL.     

MgO–TiO2–ZnO–CaO ceramics: effect of milling process on dielectric properties

The effect of grain size on the dielectric properties of MgO–TiO₂–ZnO–CaO ceramics is investigated. Attrition milling is chosen to obtain nanometre particle size from micrometre particle size powders. Additionally, the present study is focused on the effect of the nature of milling balls on ε_r, tanδ, and the temperature coefficient of capacitance (abbreviated as TCC). For that, three kinds of balls are tested: Ф1, Ф2 or Ф5 mm stabilised zirconia balls. For the samples milled by Ф2 mm balls for 10 h, the ceramics sintered at 1,270 °C showed favorable dielectric properties with ε_r = 22.6, tanδ = 1.3 × 10^?5, and TCC = 19.1 ppm/°C.     

Optical and structural investigations on iron-containing phosphate glasses

The article reports the preparation and complex characterization of iron-containing phosphate glasses considered to be ecological materials, as they contain non-toxic compounds related to environment. The oxide system Li₂O?CMgO?C(CaO)?CAl₂O₃?CP₂O₅?C(FeO/Fe₂O₃) was investigated in respect to its structural changes caused by MgO replacement with CaO and by the iron addition. UV?Cvis?CNIR (ultraviolet?Cvisible?Cnear infrared) spectroscopy as well as thermo-gravimetric (TG) measurements, differential thermo-analysis (DTA), X-ray diffraction (XRD) analysis, electronic paramagnetic resonance (EPR), and Mossbauer (nuclear gamma resonance) spectroscopy have been used to investigate redox states and coordination symmetry of iron, together with vitreous network changes during the heat treatment up to 1000 °C. UV?Cvis?CNIR transmission spectroscopy revealed no structural modifications when MgO was substituted by CaO, but noteworthy absorption bands attributed to Fe²⁺/Fe³⁺ species. TG analysis made in the 20?C1000 °C range shows low weight loss accompanied by several thermal effects, as evidenced by DTA. XRD patterns for the glass samples heat treated at about 700 °C revealed the presence of different phosphate crystalline phases containing Mg, Al, and Fe ions. EPR spectroscopy revealed the presence of paramagnetic Fe³⁺ ions and the change of the first coordination symmetry, when the samples are heated below the vitreous transition temperature. Mossbauer spectroscopy has evidenced two paramagnetic species, Fe²⁺ and Fe³⁺, both in octahedral coordination symmetry and a clustering process supported by only Fe³⁺ ions.     

Preparation of forsterite-based glass ceramics for LTCC from potassium feldspar

A forsterite-based glass ceramic material has been developed from potassium feldspar for low temperature co-fired ceramics (LTCC). The crystalline phases and microstructure of forsterite-based glass ceramics were investigated using X-ray diffraction (XRD) and field emission scanning electron microscopy (FESEM). The results show only forsterite was formed in temperature range 900–1,050 °C, and sapphirine was formed in temperature range 1,080–1,100 °C. The glass compact could be well densified at 950 °C, and full densification samples were obtained in temperature range 1,000–1,050 °C. The physical properties including dielectric properties, bending strength and thermal expansion of the specimens were also evaluated. The dielectric constants are in the range 7.00–8.25 and dielectric loss is below 0.01 in the frequency range 1–10 MHz. The specimens obtained in temperature range 950–1,100 °C are of high bending strength (69–106 MPa). The linear coefficient of thermal expansion of the specimen sintered at 1,080 °C is 9.76 × 10^?6 K^?1. All of these qualify the forsterite-based glass ceramic for further investigation as a candidate suitable for applications in LTCC field.     

Luminescence of heat-treated silicon-based polymers: promising materials for LED applications

A new strategy to obtain transparent, thermally stable, and formable photoluminescent materials for LED applications is presented. Starting from commercially available silicon-based polymers, luminescence properties are developed by means of simple heat treatment. Solid polymethylsilsesquioxane MK (Wacker-Besil^®PMS MK) and liquid poly(ureamethylvinyl)silazane Ceraset (Kion Ceraset^® PUVMS) were thermally treated between 200 and 700 °C for 2 h under Ar atmosphere. Photoluminescence properties were observed in all the samples. The structural rearrangements during thermal annealing were effective in order to red-shift the emission spectra of the untreated polymers to the visible range. The formation of dangling bonds and carbon sp², associated with the annealing procedure and confirmed by means of Electron Paramagnetic Resonance (EPR) spectroscopy and solid state Magic Angle Spinning NMR (MAS-NMR) contribute to the red-shift of the photoluminescence emissions of the polymers. After heat treatment at low temperatures (200, 300, and 400 °C), both the polymers show fluorescence in the UV range. While the polysiloxane reveals white luminescence after annealing at 500 and 600 °C, the polysilazane heat-treated at 500 °C exhibits emission in the blue-green range and is transparent. At higher temperatures the presence of free carbon counteracts the luminescence properties.     

Influence of sintering temperature on microstructures and dielectric properties of ZnO-MgO-TiO<Subscript>2</Subscript>-CaO ceramics

Microwave dielectric properties of ZnO–MgO–TiO₂–CaO (ZMTC) ceramics were investigated as a function of sintering temperatures by the conventional solid-state method. Sintering characteristics, microstructures, and microwave dielectric properties of ZMTC ceramics were studied as a function of sintering temperature from 1210 to 1290 °C. The variation trend of ε_r and Q? value was in accordance with variation trend of relative density. With increasing sintering temperature, the density, ε_r and Q? values increased, saturating at 1230 °C with excellent microwave properties of ε_r = 22.5, Q? = 22.1 × 10⁴ GHz, and TCF = 23.1 ppm/°C.     

Low-temperature sintered pollucite ceramic from geopolymer precursor using synthetic metakaolin

In this article, pollucite ceramic with high relative density and low coefficient of thermal expansion (CTE) was prepared from Cs-based geopolymer using synthetic metakaolin. Crystallization and sintering behavior of the Cs-based geopolymer together with thermal expansion behavior of the resulted pollucite ceramic were investigated. On heating at 1200 °C for 2 h, the amorphous Cs-based geopolymer completely crystallized into pollucite based on crystal nucleation and growth mechanism. Selected area diffraction analysis and XRD results confirmed the resulted pollucite ceramic at room temperature was pseudo-cubic phase with superlattice structure. Compared with Cs-based geopolymer using natural metakaolin, geopolymer using synthetic metakaolin in this article showed a much lower viscous sintering temperature range, which started at 800 °C, reached a maximum value of ?7.47 × 10^?4/°C at 1121.9 °C, and ended at 1200 °C. Cesium volatilization appeared only when temperature was above 1250 °C. Therefore, densified pollucite ceramic can be prepared from Cs-based geopolymer using synthetic metakaolin without cesium volatilization. Abnormal thermal shrinkage of pollucite ceramic was observed at temperature range from 25.3 to 54.6 °C because of pseudo-cubic to cubic phase transition, and its average CTE was 2.8 × 10^?6/°C from 25 to 1200 °C.     

Effect of CaO addition on the firing voltage of MgO films in AC plasma display panels

In order to improve both operating voltage and memory coefficient of a protective layer for AC plasma display panels, controlled amount of alkaline earth oxide (CaO) was added to the pure MgO to replace the conventional pure MgO protective layer. The effects of CaO addition on both the electrical properties (V_f and V_s) and the microstructure of the Mg_1−xCa_xO thin films deposited on slide glass substrates by e-beam evaporation were investigated. Distinct changes in both peak intensity and diffraction peak positions of Mg–Ca–O films were observed with increasing [CaO/(MgO+CaO)] ratio owing to the strong atomic interaction between Mg and Ca. When the [CaO/(MgO+CaO)] ratio was increased to 0.1, the intensities of both (111) and (200) peaks were observed to increase with corresponding peak shift to lower diffraction peak positions as a result of the strong interdiffusion from the Ca and Mg atomic interactions. When the [CaO/(MgO+CaO)] ratio of 0.1 was used, the deposited films exhibited an enhanced operating performance with an improved memory coefficient. By adding a controlled amount of CaO, the deposited Mg–Ca–O films showed a firing voltage of 176 V that is lower than that of the conventional 100% MgO film.     

Synthesis of transparent Er-doped fluorotellurite glass–ceramics through controlled crystallization

This work presents a detailed study of the preparation and microstructure of transparent glass–ceramics obtained from a TeO₂?ZnO?ZnF₂ fluorotellurite glass doped with ErF₃. The determination of nucleation and crystal growth rate-like curves allows establishing a narrow temperature range (340–350 °C) for a controlled crystallization. Thereafter, a crystalline phase was grown through a two-step heat treatment: 10–20 h at a temperature slightly above the glass transition temperature, followed by a 2.5–3 h treatment at 340 °C. Structural analysis showed the nucleation of ErF₃ nanocrystals (NCs) with a typical size of ≈50 nm that were homogeneously distributed in the glass matrix. The resulting glass–ceramic material remains highly transparent, with a small crystalline to amorphous ratio; yet the presence of ErF₃ NCs has a large impact on the photoluminescence response of Er³⁺ ions. Upconverted visible emission is analyzed under 980 nm excitation: red emission from the ⁴F_9/2 level is dramatically enhanced with respect to green ²H_11/2, ⁴S_3/2 → ⁴I_15/2 hypersensitive transitions. The observed behaviour is attributed to the presence of Er³⁺ ions in the NCs, which are sites with lower phonon energy than the glass matrix. Moreover, the shorter inter-ionic distance between Er³⁺ ions in the NCs eases energy transfer between them.