Investigation of thermoluminescence response and kinetic parameters of CaMgB2O5: Tb3+ phosphor against UV-C radiation for dosimetric application

The thermoluminescence (TL) response and kinetic parameters of CaMgB₂O₅:Tb³⁺ phosphor against UV-C radiations (λ?=?254 nm) had been investigated. The powder X-ray diffraction results confirm the formation of the monoclinic phase. TL results depict that the glow curve exhibited a broad peak centered at 430 K. The position and the shape of the curve were not influenced by the increase in dose, which is one of the requirements for dosimetric application. TL response curve was studied and showed a linear behavior against the studied dose (10–180 min). The effect of different heating rates on the TL intensity and the position of the glow peak were discussed in detail. In addition to this, the detailed examination of the glow peaks using variable heating rate and glow curve deconvolution methods was done to reveal the trapping parameters and to check the suitability of the present nanophosphor for UV-C dosimetry application.

     

Synthesis and luminescence properties of a novel Eu-doped γ-LiAlO2 phosphor

A novel phosphor, Eu³⁺-doped γ-LiAlO₂, was successfully prepared by a facile sol-gel process. The synthesis, characterization and luminescence properties of the phosphor were detailed investigated. Based on powder X-ray diffraction and scanning electron microscopy results, pure phase tetragonal LiAlO₂ was obtained by sol-gel process at 800 °C and the sphere-like particles have the diameter of 1 μm and suffer from little aggregation. Luminescence test indicated that the γ-LiAlO₂:Eu³⁺ phosphor exhibited an intense characteristic luminescence of Eu³⁺ ions, and the luminescence intensity of samples enhanced with the Eu/Li molar ratio increasing from 0.005 to 0.1.     

Development of a new-double perovskite type Sr2YZrO5.5:Eu3+ red phosphor for latent fingerprint applications

Latent fingerprint applications are playing a major role in forensic science investigations, in which the hidden impressions are illuminated using phosphors. In the present paper, a new double perovskite Eu³⁺-doped Sr₂YZrO_5.5:Eu³⁺ red phosphor was prepared through a modified solid-state reaction method and characterized by XRD, SEM and PL analysis. From XRD results, the structural phase was confirmed and further, Rietveld refinement clarified the structure. The PL emission spectra of the Sr₂YZrO_5.5:Eu³⁺ phosphors give an intense red emission at 612 nm when excited by 275 nm (CTB). The optimum dopant concentration of the Eu³⁺ ions in the present phosphor was determined. Using Ozawa’s and Dexter’s theories, the concentration quenching mechanism was obtained. The CIE values of Sr₂YZrO_5.5:Eu³⁺ (7 mol%) phosphor is found to be (0.6320, 0.3662). It has a high colour purity of 99.6%. The obtained outcomes of the present phosphor can be employed as a capable red component in latent fingerprint detection applications.

     

Combustion synthesis and luminescence properties of yellow-emitting phosphors Ca2BO3Cl:Eu2+

Yellow-emitting phosphor Ca₂BO₃Cl:Eu²⁺ was synthesized by a solution-combustion method. The phase structure and microstructure were determined by the X-ray diffraction (XRD) and scanning electron microscope (SEM) analysis, respectively. The as-prepared Ca₂BO₃Cl:Eu²⁺ phosphor absorbed near ultraviolet and blue light of 320–500 nm, and showed an intense yellow emission band centered at 569 nm with the CIE coordinate of (0.453, 0.526). The lifetime of Eu²⁺ ions in Ca₂BO₃Cl:Eu²⁺ phosphor was measured, furthermore the temperature dependent luminescence property and mechanism were studied, which also testified that the present phosphor had a promising potential for white light-emitting diodes.     

Luminescent properties of Ca2MgSi2O7 phosphor activated by Eu2+, Dy3+ and Nd3+

Long lasting alkaline earth silicates, Ca₂MgSi₂O₇:Eu,Dy,Nd was prepared under a reduction atmosphere through solid state reaction. The obtained phosphor was characterized by means of X-ray diffraction (XRD) and photoluminescence spectrum (PLS). The crystal structure of Ca₂MgSi₂O₇:Eu,Dy,Nd phosphor was refined by Rietveld analysis. The obtained Ca₂MgSi₂O₇:Eu,Dy,Nd phosphor showed a yellow–green emission peaking at 518 nm, which is ascribed to the luminescent emission of the Eu²⁺ that occupied the octa-coordinated Ca²⁺ sites in the Ca₂MgSi₂O₇ host. The electron affinity (ea) value for Eu²⁺ in [EuO₈] was calculated to 1.9 eV. The decay profile and the emission spectrum indicated that when the value of Dy/Eu is increasing, there is a concentration quenching of Eu²⁺.     

A new long persistent blue-emitting Sr2ZnSi2O7:Eu2+, Dy3+ prepared by sol–gel method

This paper reports the detailed preparation and long lasting properties of Eu²⁺-activated Sr₂ZnSi₂O₇ phosphor by sol–gel method. The preparation process of Sr₂ZnSi₂O₇ was complicated and several intermediate phases were formed during the reaction process. The obtained phosphor showed two emission peaks at 385 and 457 nm, and they were due to the different Eu²⁺ luminescent centers in Sr₂ZnSi₂O₇ host. Long afterglow was observed although the phosphor showed faint persistence. Investigation of thermoluminescence curve revealed one TL glow peak, which indicated the existence of the trap. The lifetime of the trap was calculated to be 212 s, which illustrated the faint afterglow.     

A novel blue-emitting Ca2B5O9Br:Eu2+ phosphor prepared by a microwave calcination route

A blue-emitting Ca₂B₅O₉Br:Eu²⁺ phosphor for white light-emitting diodes was synthesized via a microwave calcination route. The phosphor powders were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and fluorescence spectrophotometer, respectively. The obtained results revealed that the Ca₂B₅O₉Br:Eu²⁺ phosphor prepared by the microwave calcination route possessed a rod-like morphology with the single phase orthorhombic structure. Based on the photoluminescence analysis, it was found that Ca₂B₅O₉Br:Eu²⁺ phosphor exhibited a broad excitation band chiefly in the near ultraviolet region (270–420 nm) and a blue broad emission band of main peak at 452 nm under the strongest excitation of 411 nm. Further investigation on concentration-dependent emission spectra indicated that Ca₂B₅O₉Br:0.03Eu²⁺ phosphor exhibited the strongest luminescent intensity, and the concentration quenching for the two Eu-site emission centers was caused by dipole–dipole interactions.     

Influence of Zn2+ and Si4+ codoping on luminescence properties of CaWO4:Eu3+ phosphor

The red afterglow phosphors of CaWO₄ doped with Eu³⁺, Zn²⁺ or (and) Si⁴⁺ were prepared by solid state reaction. All crystalline phases were identified by the X-ray powder diffraction (XRD). The photoluminescence spectra and decay curves as well as thermoluminecence (TL) curves of all samples were also investigated. In comparison to CaWO₄:Eu³⁺ phosphor, the luminescence and afterglow properties could be improved greatly after being doped with Zn²⁺ or (and) Si⁴⁺ ions.     

Potential of Sr4Al14O25: Eu2+,Dy3+ inorganic oxide-based nanophosphor in Latent fingermark detection

In this paper, the potential of the Sr₄Al₁₄O₂₅: Eu²⁺,Dy³⁺ fluorescent nanophosphor is explored to visualize the latent fingermarks. The nanophosphor has been synthesized using self-propagating high temperature synthesis and shows intense luminescence and strong long after glow properties. These nano particles have been characterized for their particle size, crystalline phase, and photoluminescent properties. The calculated PL CIE co-ordinates (0.138, 0.359) correspond to the blue–green shade. Different porous, non-porous, as well as slightly non-smooth surfaces are taken and successfully tested for latent fingerprints development with the prepared Sr₄Al₁₄O₂₅: Eu²⁺,Dy³⁺ fluorescent nanophosphor powder. Present nano powder is advantageous to use on luminescent or multicolored surfaces as it gives greater contrast and also eliminates the problem of background interferences with the friction ridges due to its strong long after glow property. The results are very good when latent fingerprints were developed on the currency notes with optical variable ink and highly fluorescent pattern areas.     

Structural and optical properties of Ag2SeTe nano thin films prepared by thermal evaporation

Semiconducting Ag₂SeTe thin films were prepared with different thicknesses onto glass substrates at room temperature using thermal evaporation technique. The structural properties were determined as a function of thickness by XRD exhibiting no preferential orientation along any plane, however the films are found to have peaks corresponding to mixed phase. The XRD studies were used to calculate the crystallite size and microstrain of the Ag₂SeTe films. The calculated microstructure parameters reveal that the crystallite size increases and micro strain decreases with increasing film thickness. The refractive index, dielectric constants and thereby the optical bandgap of the films were calculated from transmittance spectral data recorded in the range 400?C1200 nm by UV?CVIS-Spectrometer. The direct optical bandgap of the Ag₂SeTe thin films deposited on glass substrates with different thicknesses 50?C230 nm were found to be in the range 1.48?C1.59 eV. The carrier density value is estimated to be around 9.8 × 10²¹ cm^?1 for the film thickness of 150 nm. The compositions estimated from the optical band gap studies reveal a value of 0.75 for Tellurium concentration. These structural and optical parameters are found to be very sensitive to the thin film thickness.     

Investigation of spectral properties of Eu<Superscript>3+</Superscript> and Tb<Superscript>3+</Superscript> doped strontium zirconium trioxide orthorhombic perovskite for optical and sensing applications

In this paper, the structural, morphological and spectral properties of Eu³⁺ and Tb³⁺ doped strontium zirconium trioxide perovskite phosphors are reported. The samples were synthesized by solid state reaction route with different doping concentrations of Eu³⁺ and Tb³⁺ ions. These synthesized phosphors were characterized by PXRD for structural analysis. The phosphors report orthorhombic structure with average crystallite size of 48 nm. FESEM and HRTEM analysis were done here for topographical and morphological studies. Also, the FTIR spectra of synthesized samples were investigated for functional group analysis. Photoluminescence and thermoluminescence spectra of synthesized samples were studied. On subjecting to 230 nm excitation, the phosphors give three distinct emissions of 596, 610 and 690 nm in the visible region corresponding to ⁵D₀ → ⁷F₁, ⁵D₀ → ⁷F₂ and ⁵D₀ → ⁷F₄ of Eu³⁺ ions. The synthesized samples were also subjected to CIE and Afterglow decay analysis. The average decay lifetime is recorded as 56.24 ns confirming the luminescence decay characteristics of short duration. In TL analysis of these phosphors, second-order kinetics with low activation energy varying from 0.50002 to 0.65668 eV is reported. The enhanced optical characteristics of prepared perovskite phosphor substantiate it as a proficient alternative for photovoltaic, optical and sensing applications.     

Structural and spectroscopic effects of Ag–Eu3+ codoping of TeO2–PbO glass ceramics

Structural and spectroscopic behavior of TeO₂–PbO–Eu₂O₃ glass ceramics containing small amounts of Ag₂O (0.5 mol%) or metallic Ag nanoparticles (AgNPs) (0.33 mol%) have been studied by varying their Eu₂O₃ content (0–10 mol%). The structural behavior of these samples was investigated by means of X-ray diffraction (XRD), SEM microscopy, and Fourier transform infrared (FTIR) spectroscopy. The average unit-cell parameters, crystallites size, and the quantitative ratio of the crystallographic phases in the samples were evaluated based on XRD data. FTIR spectroscopy data revealed that the TeO₃ and TeO₄ are the main structural units of these glass ceramics and their ratio, TeO₃/TeO₄, changes as function of the europium oxide content and the codoping of the samples. Luminescence spectroscopy measurements evidenced the important peaks located at 438, 550, and 722 nm due to the Pb²⁺ ions and at 589 and 611 nm due to the Eu³⁺ ions present in the studied samples. The presence of AgNPs in the studied glass ceramics determines a considerable enhancement of the luminescence bands of Eu³⁺ ions from 589 and 611 nm.     

Luminescence and structural properties of Eu3+ doped BaY2ZnO5 for LED solid-state lighting application

Eu³⁺ doped BaY_2(1?x)ZnO₅ phosphor was successfully synthesized by a single step solution combustion process. The crystal structure and particle morphology were investigated by X-ray diffraction (XRD), scanning electron microscopy and transmission electron microscopy. The XRD results suggest that BaY₂ZnO₅ crystallizes in a single phased orthorhombic structure with space group Pbnm at 1,100 °C. The phosphor can be effectively excited by near-UV light, emitting intense red luminescence (628 nm) corresponding to the hypersensitive ⁵D₀ → ⁷F₂ transition of Eu³⁺ ions, located at low-symmetry site with no inversion center in BaY₂ZnO₅ crystal lattice. Fluorescence decay analysis was carried out to understand the energy transfer mechanism and quenching behavior of luminescence of Eu³⁺ ions in the BaY₂ZnO₅ phosphor. The BaY₂ZnO₅: Eu³⁺ emission (λ_ex = 395 nm) could be tuned from blue to white and red light by varying the Eu³⁺ ions concentration, making this phosphor as a promising candidate for LEDs application.     

Luminescence properties and energy transfer of Ba2Mg(PO4)2:Eu2+, Mn2+ phosphor synthesized by co-precipitation method

The Ba₂Mg(PO₄)₂:Eu²⁺, Mn²⁺ phosphor is synthesized by a co-precipitation method. Crystal phase, morphology, excitation and emission spectra of sample phosphors are analyzed by XRD, SEM and FL, respectively. The results indicate particles synthesized by a co-precipitation method have a smaller size in diameter than that synthesized by conventional solid-state reaction method. Emission spectra of BMP:Eu²⁺, Mn²⁺ phosphor show a broad blue and a broad yellow emission bands with two peaks at about 456 nm and 575 nm under 380 nm excitation. An overlap between Eu²⁺ emission band and Mn²⁺ excitation band proves the existence of energy transfer from Eu²⁺ to Mn²⁺. Emitting color of the BMP:Eu²⁺, Mn²⁺ phosphor could be tuned by adjusting relative contents of Eu²⁺ and Mn²⁺ owing to energy transfer formula. Therefore, BMP:Eu²⁺, Mn²⁺ may be considered as a potential candidate for phosphor for near-UV white LED.     

Optical properties of SrAl2O4: Eu2+ phosphor in glass

Phosphor-in-glass (PiG) typed robust color converters were fabricated using pb-free silicate glasses for luminescence materials applications. The PiG based on a SiO₂–B₂O₃–BaCO₃ ternary system and SrAl₂O₄: Eu²⁺ phosphor showed good transparency reached 99.50%, even if the GTP ratio is 25:1. By simply changing the mixing ratio of glass to SrAl₂O₄: Eu²⁺ phosphor, the emission color of PiG can be controlled from blue to bluish green. The results reveal that the luminescence properties of SrAl₂O₄: Eu²⁺ distinct from the phosphor in glass significantly. These suggest that PiG could provide potential application in a variety of luminescence materials.     

Synthesis and luminescent properties of SrAl2O4:Eu green-emitting phosphor for white LEDs

SrAl₂O₄:Eu²⁺ phosphor was prepared by a solid-state reaction in CO-reductive atmosphere. X-ray powder diffraction (XRD) analysis confirmed the formation of SrAl₂O₄:Eu²⁺. Field-emission scanning electron-microscopy (FE-SEM) observation indicated that the microstructure of the phosphor consisted of irregular fine grains with an average size of about 7–8 μm. Photoluminescence measurements showed that the phosphor can be efficiently excited by UV–visible light from 350 to 430 nm, and exhibited bright green emission peaked at about 516 nm. Bright green LEDs were fabricated by incorporating the phosphor with an InGaN-based UV chip. All the characteristics indicated that SrAl₂O₄:Eu²⁺ is a good candidate phosphor applied in white LEDs.     

Band gap and trapping parameters of color tunable Yb3+/Er3+ codoped Y2O3 upconversion phosphor synthesized by combustion route

This paper reports the structural, optical and luminescence properties of Yb³⁺/Er³⁺ codoped Y₂O₃ phosphor synthesized by combustion method. The prepared phosphor was characterized by X-ray diffraction (XRD). XRD studies confirm the body-centered cubic structure of the phosphor. The optical properties such as diffuse reflectance (DR), photoluminescence and thermoluminescence were studied. DR spectra were used to determine the bandgap of the phosphor. Mechanism of upconversion by two-photon and energy transfer processes are interpreted and explained. The color coordinates were measured and the color tunability was analyzed as a function of the 980 nm excitation source power. Different trapping parameters associated with the glow peak were calculated by various glow curve methods.     

Synthesis and characterisation of LiB3 O5 nanophosphor as a TL dosimeter

In this work, lithium triborate (LiB₃ O₅) nanophosphor was synthesised by precipitation assisted high‐temperature solid‐state method followed by heating at different sintering temperatures. Then, its crystal structure and morphology were fully characterised. LiB₃ O₅ was doped with different concentrations of different dopants. To determine the thermoluminescence (TL) properties and structural specifications of doped lithium triborate, the sample was irradiated by photons and then, its TL glow curve was obtained using a TL dosimeter‐reader system. To study the effect of heating rate (HR) on TL characterisation of this nanophosphor, TL measurements were done at different HRs. The results showed that, sintering temperature can affect the morphology and structural properties of lithium triborate and consequently its TL intensity. The findings also showed that the LiB₃ O₅ :Al nanophosphor with the dopant concentration of 2 wt.% has the highest sensitivity and the best peak position among the studied activators. The results of the HR method showed that this method may be provided accurate calculations of the physical parameters of the TL process. These results may be helpful in the development of tissue equivalent TL nanocrystalline detectors usable in medical and personnel dosimetry.Inspec keywords: thermoluminescent dosimeters, sintering, phosphors, crystal structure, dosimetry, thermoluminescence, lithium compounds, nanostructured materials, nanofabrication, aluminiumOther keywords: high‐temperature solid‐state method, crystal structure, morphology, thermoluminescence properties, structural specifications, doped lithium triborate, TL glow curve, TL dosimeter‐reader system, heating rate, TL characterisation, TL measurements, sintering temperature, structural properties, TL intensity, nanophosphor, dopant concentration, HR method, TL process, tissue equivalent TL nanocrystalline detectors, LiB₃ O₅ :Al     

Synthesis of monodisperse spherical core-shell SiO2-SrAl2Si2O8: Eu2+ phosphors by hydrothermal homogeneous precipitation method

Abstract

Nanocrystalline SrAl₂Si₂O₈ :Eu²⁺ phosphor layers were coated on nonaggregated, monodisperse and spherical SiO₂ particles using a hydrothermal homogeneous precipitation. After annealing at 1100 °C, core-shell SiO₂@SrAl₂Si₂O₈ :Eu²⁺ particles were obtained. They were characterized with x-ray diffraction (XRD), scanning electron microscopy, transmission electron microscopy and photoluminescence techniques. XRD analysis confirmed the formation of SiO₂ @SrAl₂Si₂O₈ :Eu²⁺ particles; it indicated that the SrAl₂Si₂O₈ :Eu²⁺ shells on SiO₂ particles consisted of hexagonal crystallites. The core-shell phosphors obtained are well-dispersed submicron spherical particles with a narrow size distribution. The thickness of the coated layer is approximately 20–40 nm. Under ultraviolet excitation (361 nm), the particles emit blue light at about 440 nm due to the Eu²⁺ ions in their shells.     

Synthesis and efficient blue-emitting of Eu2+-activated borate fluoride BaAlBO3F2

Eu²⁺-doped borate fluoride BaAlBO₃F₂ was synthesized by the conventional high temperature solid state reaction. The crystal phase formations were confirmed by X-ray powder diffraction (XRD) measurements and the structure refinement. The photoluminescence (PL) excitation and emission spectra, and the decay curves were investigated. Eu²⁺-doped BaAlBO₃F₂ phosphor can be efficiently excited by near-UV light and presents narrow blue luminescence band centered at 450 nm. The maximum absolute quantum efficiency (QE) of BaAlBO₃F₂:0.05Eu²⁺ phosphor was measured to be 76% excited at 398 nm light at 300 K. The thermal stability of the blue luminescence was evaluated by the luminescence decays as a function of temperature. The phosphor shows an excellent thermal stability with high thermal activation-energy on temperature quenching effects because of the rigid crystal lattices.