Photoluminescence and piezoelectric behaviour of Y2Zr2O7 pyrochlore‐based multifunctional materials and the influence of Eu3+ and Sm3+

Y₂Zr₂O₇‐doped with Eu³⁺ and Sm³⁺ phosphors were prepared for the first time as multifunctional smart materials using a solid‐state reaction method at 1400^oC. Thermal behaviour, crystal structure, surface morphology, and elemental analysis were characterized using thermogravimetric (TG) and differential thermal (DTA) analyses, X‐ray diffraction (XRD) and scanning electron microscope equipped with energy‐dispersive X‐ray spectroscopy (SEM‐EDX). Experimental results revealed that both phosphors have a pyrochlore structure with a cubic crystal system. Photoluminescence properties were also measured and red emission was observed from Y_1.90Eu_0.10Zr₂O₇ and Y_1.90Sm_0.10Zr₂O₇ phosphors. Dielectric constant, loss tangent, piezoelectric charge constant, and Curie temperature of all the samples were determined using an LCR‐meter, d₃₃‐meter, and TG/DTA. Eu doping in Y₂Zr₂O₇ resulted in a high dielectric constant (9.61) and low loss tangent (1.67%) values, whereas high piezoelectric charge constant (0.68 pC/N) and high Curie temperature (820°C) could be obtained using Sm‐doped Y₂Zr₂O₇.     

Synthesis and characterization of novel europium β‐diketonate organic complexes for solid‐state lighting

Volatile Eu complexes, namely Eu(TTA)₃Phen, Eu_(x)Y_(1‐x)(TTA)₃ Phen; Eu_(x)Tb_(1‐x)(TTA)₃Phen; Eu, europium; Y, yttrium; Tb, Terbium; TTA, thenoyltrifluoroacetone; and Phen, 1,10 phenanthroline were synthesized by maintaining stichiometric ratio. Various characterization techniques such as X‐ray diffraction (XRD), photoluminescence (PL) and thermo gravimetric analysis/differential thermal analysis (TGA/DTA) were carried out for the synthesized complexes. Diffractograms of all the synthesized complexes showed well‐resolved peaks, which revealed that pure and doped organic Eu³⁺ complexes were crystalline in nature. Of all the synthesized complexes, Eu_0.5 Tb_0.5(TTA)₃Phen showed maximum peak intensity, while the angle of maximum peak intensity for all complexes was almost the same with slightly different d‐values. A prominent sharp red emission line was observed at 611 nm when excited with light at 370 nm. It was observed that the intensity of red emissions increased for doped europium complexes Eu_(x)Y_(1‐x)(TTA)₃Phen and Eu_(x)Tb_(1‐x)(TTA)₃ Phen, when compared with Eu complexes. Emission intensity increased in the following order: Eu(TTA)₃Phen > Eu_0.5 Tb_0.5(TTA)₃Phen > Eu_0.4 Tb_0.6(TTA)₃Phen > Eu_0.5Y_0.5(TTA)₃Phen > Eu_0.4Y_0.6(TTA)₃Phen, proving their potential application in organic light‐emitting diodes (OLEDs). TGA showed that Eu complexes doped in Y³⁺ and Tb³⁺ have better thermal stability than pure Eu complex. DTA analysis showed that the melting temperature of Eu(TTA)₃ Phen was lower than doped Eu complexes. These measurements infer that all complexes were highly stable and could be used as emissive materials for the fabrication of OLEDs. Copyright © 2012 John Wiley & Sons, Ltd.     

Luminescence properties of barium – gadolinium–titanate ceramics doped with rare‐earth ions (Eu3+ and Tb3+)

Barium‐gadolinium‐titanate (BaGd₂Ti₄O₁₂) powder ceramics doped with rare‐earth ions (Eu³⁺ and Tb³⁺) were synthesized by a solid‐state reaction method. From the X‐ray diffraction spectrum, it was observed that Eu³⁺ and Tb³⁺:BaGd₂Ti₄O₁₂ powder ceramics are crystallized in the form of an orthorhombic structure. Scanning electron microscopy image shows that the particles are agglomerated and the particle size is about 200 nm. Eu³⁺‐ and Tb³⁺‐doped BaGd₂Ti₄O₁₂ powder ceramics were examined by energy dispersive X‐ray analysis, Fourier transform infrared spectroscopy, photoluminescence and thermoluminescence (TL) spectra. Emission spectra of Eu³⁺‐doped BaGd₂Ti₄O₁₂ powder ceramics showed bright red emission at 613 nm (⁵D₀ → ⁷F₂) with an excitation wavelength λ_exci = 408 nm (⁷F₀ → ⁵D₃) and Tb³⁺:BaGd₂Ti₄O₁₂ ceramic powder has shown green emission at 534 nm (⁵D₄ → ⁷F₅) with an excitation wavelength λ_exci = 331 nm ((⁷F₆ → ⁵D₁). TL spectra show that Eu³⁺ and Tb³⁺ ions affect TL sensitivity. Copyright © 2014 John Wiley & Sons, Ltd.     

Structural,morphological and steady state photoluminescence spectroscopy studies of red Eu3+‐doped Y2O3 nanophosphors prepared by the sol‐gel method

Europium trivalent (Eu³⁺)‐doped Y₂O₃ nanopowders of different concentrations (0.5, 2.5, 5 or 7 at.%) were synthesized by the sol‐gel method, at different pH values (pH 2, 5 or 8) and annealing temperatures (600°C, 800°C or 1000°C). The nanopowders samples were characterized by X‐ray diffraction (XRD), field emission scanning electron microscopy (FE‐SEM), Fourier transform infrared spectroscopy (FT‐IR) and steady state photoluminescence spectroscopy. The effect of pH of solution and annealing temperatures on structural, morphological and photoluminescence properties of Eu³⁺‐doped Y₂O₃ were studied and are discussed. It was found that the average crystallite size of the nanopowders increased with increasing pH and annealing temperature values. The Y₂O₃:Eu³⁺ material presented different morphology and its evolution depended on the pH value and the annealing temperature. Activation energies at different pH values were determined and are discussed. Under ultraviolet (UV) light excitation, Y₂O₃:Eu³⁺ showed narrow emission peaks corresponding to the ⁵D_0–⁷F_J (J = 0, 1, 2 and 3) transitions of the Eu³⁺ ion, with the most intense red emission at 611 assigned to forced electric dipole ⁵D₀→⁷F₂. The emission intensity became more intense with increasing annealing temperature and pH values, related to the improvement of crystalline quality. For the 1000°C annealing temperature, the emission intensity presented a maximum at pH 5 related to the uniform cubic‐shaped particles. It was found that for lower annealing temperatures (small crystallite size) the CTB (charge transfer band) position presented a red shift. Copyright © 2015 John Wiley & Sons, Ltd.     

The structure and luminescence properties of Mn2+/Eu2+/Er3+‐doped MgO‐Ga2O3‐SiO2 glasses and glass‐ceramics

The MgO–Ga₂O₃–SiO₂ glasses and glass‐ceramics samples doped with Eu²⁺/Mn²⁺/Er³⁺ and heated in reductive atmosphere were prepared by the sol–gel method. The structure, morphology and the luminescence properties were studied using X‐ray diffraction, high‐resolution transmission electron microscope, fluorescence spectra, and up‐conversion emission. The luminescence characteristics of doped ions could be influenced by temperature and matrix component. The characteristic emission of Mn²⁺, Eu²⁺ and Er³⁺ were seen and the energy transfer efficiency from Eu²⁺ to Mn²⁺ was enhanced as Mn²⁺ concentration was increased. In addition, the two‐photon process was determined for the Er³⁺‐doped samples.     

Sol–gel preparation and luminescent properties of red‐emitting phosphor Sr‐Ba‐Mo‐W‐O‐(Eu3+,Sm3+)

Two series of red‐emitting phosphors Sr‐Ba‐Mo‐W‐O:Eu,Sm and Sr‐Ba‐Mo‐W‐O:Eu have been synthesized by a sol–gel method. The effects of the chemical composition, concentrations of Sm³⁺ and Eu³⁺, the Sr²⁺/Ba²⁺ ratio, and the W⁶⁺/Mo⁶⁺ ratio on the luminescent properties were investigated. The as‐prepared phosphors were characterized by X‐ray diffraction and Raman spectra. Results showed that single phases of the two series were prepared. The compositions of Sr_0.6Ba_0.13Mo_0.8 W_0.2O₄:Eu_0.10Sm_0.08 and Sr_0.75Ba_0.1Mo_0.8 W_0.2O₄:Eu_0.10 had the strongest luminescent intensity. The excitation spectra of Sm³⁺, Eu³⁺ co‐doped phosphors were broader and the strongest peak moved to 404 nm when compared with that of Eu³⁺ single‐doped phosphors. The luminescent intensity of the Sr_0.6Ba_0.13Mo_0.8 W_0.2O₄:Eu_0.10Sm_0.08 at 618 nm were 2.8 times greater than that of Sr_0.75Ba_0.1Mo_0.8 W_0.2O₄:Eu_0.10. The luminescent intensity of Sr_0.6Ba_0.13Mo_0.8 W_0.2O₄:Eu_0.10Sm_0.08 and Sr_0.75Ba_0.1Mo_0.8 W_0.2O₄:Eu_0.10 at 150 °C decreased to 56.8% and 50.3% of the initial value at room temperature, respectively. Copyright © 2015 John Wiley & Sons, Ltd.     

Molten salt synthesis and luminescence of Dy3+‐doped Y3Al5O12 phosphors

Dy³⁺‐doped Y₃Al₅O₁₂ phosphors were prepared at a relatively low temperature using molten salt synthesis. The phase of the prepared Dy³⁺‐doped Y₃Al₅O₁₂ phosphors was confirmed using X‐ray powder diffraction. Results indicated that Dy³⁺ doping did not change the Y₃Al₅O₁₂ phase. Following excitation at 352 nm, emission spectra of the Dy³⁺‐doped Y₃Al₅O₁₂ phosphors consisted of blue, yellow, and red emission bands. The influence of Dy³⁺ concentration and excitation wavelength on emission was investigated. The ratio of yellow light to blue light varied with change in Dy³⁺ doping concentration, due to changes in the structure around Dy³⁺. Emission intensities also changed when the excitation wavelength was changed. This variation is luminescence generated a system for tunable white light for Dy³⁺‐doped Y₃Al₅O₁₂ phosphors.     

Luminescence properties of green‐emitting Ca2MgSi2O7:Eu2+ phosphor by a solid‐state reaction method

A europium (Eu)‐doped di‐calcium magnesium di‐silicate phosphor, Ca₂MgSi₂O₇:Eu²⁺, was prepared using a solid‐state reaction method. The phase structure, particle size, surface morphology, elemental analysis, different stretching mode and luminescence properties were analyzed by X‐ray diffraction (XRD), transmission electron microscopy (TEM), field emission scanning electron microscopy (FESEM) with energy dispersive X‐ray spectroscopy (EDX), Fourier transform infrared (FTIR) spectroscopy, photoluminescence (PL) and mechanoluminescence (ML). The phase structure of Ca₂MgSi₂O₇:Eu²⁺ was an akermanite‐type structure, which belongs to the tetragonal crystallography with space group P4?2₁m; this structure is a member of the melilite group and forms a layered compound. The surface of the prepared phosphor was not found to be uniform and particle distribution was in the nanometer range. EDX and FTIR confirm the components of Eu²⁺‐doped Ca₂MgSi₂O₇ phosphor. Under UV excitation, the main emission peak appeared at 530 nm, belonging to the broad emission ascribed to the 4f⁶5d¹→4f⁷ transition of Eu²⁺. The ML intensity of the prepared phosphor increased linearly with increasing impact velocity. A CIE color chromaticity diagram and ML spectrum confirmed that the prepared Ca₂MgSi₂O₇:Eu²⁺ phosphor would emit green color and the ML spectrum was similar to that of PL, which indicated that ML is emitted from the same center of Eu²⁺ ions. Copyright © 2015 John Wiley & Sons, Ltd.     

Synthesis and photoluminescence properties of red emitting phosphor La2–xEuxLi0.5Al0.5O4 [x = 0.2–2] with K2NiF4 structure

Europium (Eu)³⁺‐substituted La₂Li_0.5Al_0.5O₄ red emitting phosphors were prepared by a conventional high‐temperature solid‐state reaction method. Powder X‐ray diffraction, diffuse reflectance spectra and spectrofluorometry were used as vital characterizing tools for the phosphors. The Eu concentration dependence luminescence properties and Judd–Ofelt intensity parameters were investigated and calculated, respectively. All compositions showed an orange red emission (due to the magnetic and electric dipole transitions of the Eu³⁺ ion) with the appropriate Commission Internationale de l'Eclairage (CIE) colour gamut under near ultraviolet or blue ray light excitation. The calculated critical distance showed that the energy transfer occured between Eu to Eu via an exchange mechanism. The Eu_1.4La_0.6Li_0.5Al_0.5O₄ composition showed the highest red emission intensity with CIE colour saturation compared with that of the commercial Eu‐activated yttrium oxysulfide red phosphor.     

Synthesis and characterization of Y(1‐x)Eu(x)(TTA)3(Phen) organic luminescent thin films

Yttrium is stoichiometrically doped into europium by mole percentage, during the synthesis of Y_(1‐x)Eu_(x)(TTA)₃(Phen), using solution techniques (where x = 0.2, 0.4, 0.5, 0.6 and 0.8, TTA = thenoyltrifluoroacetone and Phen = 1,10‐phenanthroline).These complexes were characterized using different techniques such as X‐ray diffraction, thermogravimetric/differential thermal analysis, optical absorption and emission spectra. Thin films of the doped Eu–Y complexes were prepared on a glass substrate under a high vacuum of 10^‐6 Torr. The photoluminescence spectra of these thin films were recorded by exciting the sample at a wavelength of 360 nm. The emission peak for all the synthesized complexes centered at 611 nm; maximum emission intensity was obtained from Y_0.6Eu_0.4 (TTA)₃(Phen). The results proved that these doped complexes are more economical than pure Eu(TTA)₃(Phen) and are best suited as red emissive material for energy‐efficient and eco‐friendly organic light‐emitting diodes and displays. Copyright © 2013 John Wiley & Sons, Ltd.     

Synthesis and luminescence study of Eu3+‐doped SrYAl3O7 phosphor

Rare‐earth ions play an important role in eco‐friendly solid‐state lighting for the lighting industry. In the present study we were interested in Eu³⁺ ion‐doped inorganic phosphors for near ultraviolet (UV) excited light‐emitting diode (LED) applications. Eu³⁺ ion‐activated SrYAl₃O₇ phosphors were prepared using a solution combustion route at 550°C. Photoluminescence characterization of SrYAl₃O₇:Eu³⁺ phosphors showed a 612 nm emission peak in the red region of the spectrum due to the ⁵D₀→⁷F₂ transition of Eu³⁺ ions under excitation at 395 nm in the near‐UV region and at the 466 nm blue excitation wavelength. These red and blue emissions are supported for white light generation for LED lighting. Structure, bonding between each element of the sample and morphology of the sample were analysed using X‐ray diffraction (XRD) and scanning electron microscopy (SEM), which showed that the samples were crystallized in a well known structure. The phosphor was irradiated with a ⁶⁰Co‐γ (gamma) source at a dose rate of 7.2 kGy/h. Thermoluminescence (TL) studies of these Eu³⁺‐doped SrYAl₃O₇ phosphors were performed using a Nucleonix TL 1009I TL reader. Trapping parameters of this phosphor such as activation energy (E), order of kinetics (b) and frequency factor (s) were calculated using Chen's peak shape method, the initial rise method and Ilich's method.     

Pure rhombohedral Bi1‐xEuxPO4 nano‐/micro‐structures: fast synthesis,shape evolution and luminescence properties

BiPO₄ and Eu‐doped BiPO₄ crystals were synthesized via a simple precipitation route at room temperature , employing Bi ( NO₃ ) ₃ and ( NH₄ ) ₂HPO₄ as the reactants , Eu₂O₃ as the dopant and citric acid as a template . X‐ray powder diffraction analyses showed that pure rhombohedral BiPO₄ form was obtained , and was the preferential orientation growth of the crystal . Field emission scanning electron microscope observations showed that the concentration of Bi ^{3 +} obviously changed the products ' morphologies from nanosphere , hollow sphere to hexagonal prism . The acidity of the solution and the contents of citric acid and Eu ^{3 +} ion tailored the size of the final crystals . Effects of concentration of Eu ^{3 +} ion on the luminescence emission intensity were also investigated . Copyright © 2015 John Wiley & Sons, Ltd.     

Enhancement of the photoluminescence and long afterglow properties of Sr2MgSi2O7:Eu2+ phosphor by Dy3+ co‐doping

Sr₂MgSi₂O₇:Eu²⁺ and Sr₂MgSi₂O₇:Eu²⁺,Dy³⁺ long afterglow phosphors were synthesized under a weak reducing atmosphere by the traditional high temperature solid state reaction method. The synthesized phosphors were characterized by powder X‐ray diffraction (XRD), energy dispersive X‐ray spectroscopy (EDX), and photo‐, thermo‐ and mechanoluminescence spectroscopic techniques. The phase structure of the sintered phosphor was an akermanite type structure, which belongs to tetragonal crystallography. The thermoluminescence properties of these phosphors were investigated and compared. Under ultraviolet light excitation, the emission spectra of both prepared phosphors were composed of a broad emission band peaking at 470 nm. When the Sr₂MgSi₂O₇:Eu²⁺ phosphor was co‐doped with Dy³⁺, the photoluminescence (PL), afterglow and mechanoluminescence (ML) intensity were strongly enhanced. The decay graph indicated that both the sintered phosphors contained fast decay and slow decay processes. The ML intensities of Sr₂MgSi₂O₇:Eu²⁺ and Sr₂MgSi₂O₇:Eu²⁺,Dy³⁺ phosphors were increased proportionally with increasing impact velocity, a finding that suggests that these phosphors could be used as sensors to detect the stress of an object. Copyright © 2015 John Wiley & Sons, Ltd.     

Zn‐doped CaTiO3:Eu3+ red phosphors for enhanced photoluminescence in white LEDs by solid‐state reaction

Zn‐doped CaTiO₃:Eu³⁺ red phosphors for enhanced photoluminescence in white light‐emitting diodes (LEDs) were synthesized by a solid‐state method. The structure and morphology of the obtained phosphor samples were observed by X‐ray diffraction (XRD) and scanning electron microscopy (SEM), and the impact of Ca, Zn and Eu content on their photoluminescence properties was studied. The results indicated that Zn not only participates in the formation of defects in suitable lattice matrices but also has a role in flux in the transformation from ZnO to Zn₂TiO₄, which is beneficial for the enhancement of photoluminescence properties. Photoluminescence test data showed that the Zn‐doped phosphor is excited efficiently by near‐ultraviolet (NUV) light at wavelengths around 398 nm and emits an intense red light with a broad peak around 616 nm corresponding to the ⁵D₀→⁷F₂ transition of Eu³⁺. The intensity of this phosphor emission is three times stronger than that without Zn‐doping. Furthermore, this phosphor has very good thermal stability, high color purity and a low sintered temperature, all of which suggest its potential as a promising red phosphor for white LEDs. Copyright © 2015 John Wiley & Sons, Ltd.     

Effect of replacement of Ca by Zn on the structure and optical property of CaTiO3:Eu3+ red phosphor prepared by sol‐gel method

Eu³⁺‐doped calcium titanate red phosphors, Ca_1‐xZn_xTiO₃:Eu³⁺, were prepared by the sol‐gel method. The structure of prepared Ca_1‐xZn_xTiO₃:Eu³⁺ phosphors were investigated by X‐ray diffraction and infrared spectra. Due to the ⁵D₀ → ⁷F_1–3 electron transitions of Eu³⁺ ions, photoluminescence spectra showed a red emission at about 619 nm under excitation of 397 nm and 465 nm, respectively. When zinc was added to the host, the luminescent intensity of Ca_1‐xZn_xTiO₃:Eu³⁺ was markedly improved several fold compared with that of CaTiO₃:Eu³⁺. Ca_0.9Zn_0.1TiO₃:Eu³⁺ also had higher luminescence intensity than the commercially available Y₂O₃:Eu³⁺ phosphors under UV light excitation. Copyright © 2014 John Wiley & Sons, Ltd.     

Synthesis and photoluminescence properties of Sm3+‐doped YAl3(BO3)4 phosphor

A near ultraviolet excitable phosphor based on Sm³⁺‐doped YAl₃(BO₃)₄ has been synthesized by modified solid‐state reaction at 1000°C. The phase purity and photoluminescence (PL) behavior of the phosphor are studied in detail using the powder X‐ray diffraction technique and PL measurements. X‐ray diffraction reveals that the phase purity of YAl₃(BO₃)₄ critically depends upon the boric acid concentration. The phosphor has strong excitation at 406 nm in the near ultraviolet region (350–420 nm) and its emission peaks were monitored at 564, 599 and 643 nm. Further, detailed PL analysis demonstrates that the substitution of Sm³⁺ ions at sites of Y³⁺ and Al³⁺ ions enhances the PL efficiency of the phosphor appreciably. First, the PL efficiency of YAl₃(BO₃)₄:Sm³⁺ was compared with commercial (Y,Gd)BO₃:Eu³⁺ red phosphor. The Fourier transform infrared study provides essential information regarding the change in metal–oxygen bond vibrations of the phosphor. The morphology of the phosphor was investigated through scanning electron microscopy, which reveals that the phosphor possessed distorted spherical and rectangular shapes with average grain sizes in the range 0.5–1 µm. Copyright © 2013 John Wiley & Sons, Ltd.     

Two‐ step synthesis and luminescent properties of BaB2O4:Eu3+ nano/microphosphors prepared from Ba‐B‐O:Eu3+ precursor

The BaB₂O₄:Eu³⁺ nano/microphosphors with sphere‐, rod‐, and granular‐like morphologies were successfully obtained by a two‐step method using Ba‐B‐O:Eu³⁺ as the precursor. The structure, morphology and photoluminescent properties of the products were characterized by Fourier transfer infrared spectroscopy (FT‐IR), X‐ray diffraction (XRD), thermogravimetry‐differential thermal analysis (TG‐DTA), scanning electron microscopy (SEM) and photoluminescence (PL). The formation mechanisms of Ba‐B‐O:Eu³⁺ and BaB₂O₄:Eu³⁺ were proposed. The results show that the BaB₂O₄:Eu³⁺ could retain the original morphologies of their respective precursors largely. The BaB₂O₄:Eu³⁺ prepared by this two‐step method exhibited better morphology, smaller particle size and better crystallinity than when prepared by a solid‐state method. The granular‐like BaB₂O₄:Eu³⁺ red phosphor prepared by this two‐step method exhibited stronger PL intensity and better red color purity than when prepared by a solid‐state method.     

Tunable luminescence properties and energy transfer in LaAl11O18:Eu,Tb phosphor

Eu²⁺ and Tb³⁺ singly doped and co‐doped LaAl₁₁O₁₈ phosphors were prepared by a combustion method using urea as a fuel. The phase structure and photoluminescence (PL) properties of the prepared phosphors were characterized by powder X‐ray diffraction (XRD), scanning electron microscopy (SEM), and photoluminescence excitation and emission spectra. When the content of Eu²⁺ was fixed at 0.01, the emission chromaticity coordinates could be adjusted from blue to green region by tuning the contents of Tb³⁺ ions from 0.01 to 0.03 through an energy transfer (ET) process. The fluorescence data collected from the samples with different contents of Tb³⁺ into LaAl₁₁O₁₈: Eu, show the enhanced green emission at 545 nm associated with ⁵D₄ –⁷F₅ transitions of Tb³⁺. The enhancement was attributed to ET from Eu²⁺ to Tb³⁺, and therefore Eu²⁺ ion acts as a sensitizer (an energy donor) while Tb³⁺ ion as an activator. The ET from Eu²⁺ to Tb³⁺ is performed through dipole–dipole interaction. The ET efficiency and critical distance were also calculated. The present Eu²⁺–Tb³⁺ co‐doped LaAl₁₁O₁₈ phosphor will have potential application for UV convertible white light‐emitting diodes. Copyright © 2015 John Wiley & Sons, Ltd.     

ZnWO4:Eu3+ phosphor with intense blue LED excitation: photoluminescence and electron density distribution analysis

A high intensity 464 nm excitable ZnWO₄:Eu³⁺ red‐emitting phosphor for warm white lighting applications was prepared using a solid‐state reaction method by varying the dopant Eu³⁺ concentration. Crystalline purity and phase identification was confirmed and revealed using powder X‐ray diffraction and Rietveld refinement analysis. The surface morphology of Zn_1‐xEu_xWO₄ (x = 0, 0.01, 0.02, 0.03, 0.04 and 0.05) was examined using scanning electron microscopy (SEM) techniques. From SEM analysis, the ZnWO₄:Eu³⁺ phosphor prepared at 1–3% molar Eu³⁺ concentrations exhibited a small pebble‐like morphology with a smooth surface. On increasing the molar concentration of Eu³⁺ to >3%, the pebble stone morphology disappeared and a large, smooth irregular polygon‐shaped granular‐like morphology was obtained. Of the higher mol% Eu³⁺, the 4% Eu³⁺‐doped ZnWO₄ showed the best photoluminescence properties with high intensity and sharp excitation at 395 and 464 nm, followed by red emission centred at 615 nm with excellent CIE coordinates (x = 0.58 and y = 0.41) in the core red region. Elemental composition and chemical state analysis were carried out for the 4% Eu³⁺‐doped ZnWO₄ phosphor using X‐ray photoelectron spectroscopy and energy dispersive X‐ray spectroscopy studies. Based on all the above analyses, the Eu³⁺‐doped ZnWO₄ phosphor was found to be a very efficient red‐emitting phosphor under near‐UV light as well as under visible light excitation and could be used for white LED and field emissive displays applications.     

Studies on the luminescence properties of cerium co‐doping on Ca2MgSi2O7:Eu2+ phosphor by solid‐state reaction method

Ca₂MgSi₂O₇:Ce³⁺, Ca₂MgSi₂O₇:Eu²⁺ and Ca₂MgSi₂O₇:Eu²⁺,Ce³⁺ phosphors were prepared using the solid‐state reaction method. The crystal structures of the sintered phosphors were of melilite type, which has a tetragonal crystallography. The chemical compositions of the sintered phosphors was confirmed by energy dispersive X‐ray spectroscopy. The different thermoluminescence kinetic parameters [activation energy (E), frequency factor (s) and order of the kinetics (b)] of these phosphors were evaluated and compared using the peak shape method. Under ultraviolet excitation, the emission spectra of both Ca₂MgSi₂O₇:Eu²⁺ and Ca₂MgSi₂O₇:Eu²⁺,Ce³⁺ phosphors were composed of a broad emission band peaking at 530 nm. When the Ca₂MgSi₂O₇:Eu²⁺ phosphor is co‐doped with Ce³⁺ ions, photoluminescence, afterglow and mechanoluminescence intensity was strongly enhanced. Ca₂MgSi₂O₇:Eu²⁺ showed some afterglow with a short persist time. On incorporation of Ce³⁺, efficient energy transfer from Ce³⁺ to Eu²⁺ was found and the emission intensity of Eu²⁺ was enhanced. The mechanoluminescence intensities of Ca₂MgSi₂O₇:Ce³⁺, Ca₂MgSi₂O₇:Eu²⁺ and Ca₂MgSi₂O₇:Eu²⁺,Ce³⁺ phosphors increased proportionally increased with the increase in impact velocity, which suggests that these phosphors can be used as sensors to detect stress in an object.