Synthesis and optical properties of europium doped zinc silicate prepared using low cost solid state reaction method

This paper presents a study on synthesis and optical properties of Zn₂SiO₄:1 wt% Eu³⁺ at different heat treatments. The objective of the research is to synthesize Zn₂SiO₄:1 wt% Eu³⁺ phosphor by using low cost solid state reaction method with recycled waste bottle glasses as the silicate source. The X-ray diffraction results showed that the prepared Zn₂SiO₄:1 wt% Eu³⁺ phosphors have a sharp diffraction peak as the heat treatment temperatures were increased from 600 to 1000 °C. Furthermore, the morphology from the Field emission scanning electron microscope analysis were shown the formation of well crystalline samples with dense packed grains due to the increment of heat treatment temperatures. Fourier transform infrared spectra has confirmed the present elements in Zn₂SiO₄:1 wt% Eu³⁺ phosphors while the narrow width of Raman line spectra were observed at temperatures ranging from 700 to 1000 °C indicates good homogeneity and crystallinity of synthesized powders. In addition, the energy band gap of europium doped zinc silicate increased dramatically up to 3.62 eV at temperature of 1000 °C. Photoluminescence measurements has also exhibited the red emission corresponding to the ⁵D₀ → ⁷F₂ (600 nm) when viewed under blue excitation.     

Synthesis and characterizations of Dy3+ doped Sr3Al2O6:Eu2+ powder phosphors through citric acid precursor

Sr₃Al₂O₆:Eu²⁺, Dy³⁺ phosphors were synthesized by the polymer precursor method. The X-ray powder diffraction patterns show that the samples have a cubic structure with a space group of Pa3. In the excitation spectrum, the phosphors show a wide absorption in the UV region from 250 to 450 nm, which corresponds to the crystal field splitting of the Eu²⁺ d-orbital. All the emission spectrum of Sr₃Al₂O₆:Eu²⁺, Dy³⁺ phosphors show the broad band emission peaked at about 518 nm, which can be ascribed to the typical 4f⁶5d¹ → 4f⁷ transitions of Eu²⁺ ions. And the best dopant concentration of Dy³⁺ ions for Sr₃Al₂O₆:2 mol%Eu²⁺, xDy³⁺ phosphors is 2 mol%. The excitation wavelengths have no influences on emission peaks, but have clear influences on emission intensities.     

Enhanced luminescence in CaMoO4: Eu3+ red phosphor nanoparticles prepared by mechanochemically assisted solid state meta-thesis reaction method

For the first time, CaMoO₄: xEu³⁺ (x = 0.02, 0.04, 0.06, 0.08, 0.1) red phosphor nanoparticles were synthesized using the simple mechanochemically assisted solid state meta-thesis (SSM) reaction method and the luminescence properties as a function of Eu³⁺ ion concentration was investigated. The characteristics of the phosphor materials were analyzed using X-ray diffraction, fourier transform infrared spectroscopy, photoluminescence (PL) and diffuse reflectance spectroscopy. For 8 mol% of Eu³⁺ concentration, the phosphor shows an intensified excitation peak at 392 nm indicating a strong absorption. The PL emission spectra of CaMoO₄: Eu³⁺ phosphors showed an intense peak at 615 nm (red) which corresponds to ⁵D₀ → ⁷F₂ transition of Eu³⁺. The optimal Eu³⁺ concentration in CaMoO₄ phosphors for enhanced red emission occurs for 8 mol% and above this concentration, the emission intensity decreases due to quenching effect. The CIE colour coordinates of the CaMoO₄: 0.08Eu³⁺ red phosphor coincide very well with the standard values of NTSC. The red emission intensity of the SSM prepared CaMoO₄: 0.08Eu³⁺ red phosphor is 4.7 times greater than that of the commercial Y₂O₂S: Eu³⁺ red phosphor and 1.6 times more than the same phosphor prepared by the solid state reaction method.     

Hydrothermal synthesis of NaLa(WO<Subscript>4</Subscript>)<Subscript>2</Subscript>:Eu<Superscript>3+</Superscript> octahedrons and tunable luminescence by changing Eu<Superscript>3+</Superscript> concentration and excitation wavelength

NaLa(WO₄)₂:Eu³⁺ phosphors with different Eu³⁺ concentrations have been synthesized by a hydrothermal method. The phase is confirmed by XRD analysis, which shows a pure-phase NaLa(WO₄)₂ XRD pattern for all of NaLa(WO₄)₂:Eu³⁺ phosphors. The SEM and TEM images indicate that all of NaLa(WO₄)₂:Eu³⁺ phosphors have a octahedral morphology. These suggest that the Eu³⁺ doping has no influence on the structure and growth of NaLa(WO₄)₄ particles. By monitoring the emission of Eu³⁺ at 615 nm, NaLa(WO₄)₂:Eu³⁺ phosphors show excitation bands originating from both host and Eu³⁺ ions. Under the excitation at 271 nm corresponding to WO₄ ^2? groups, emission bands coming from the ¹A₁ → ³T₁ transition with the WO₄ ^2? groups and the ⁵D₀ → ⁷F_j (j = 0, 1, 2, 3 and 4) transitions of Eu³⁺ are observed. The emission intensity relating to WO₄ ^2? groups decreases with increasing Eu³⁺ concentration. But emission intensities of Eu³⁺ increase firstly and then decreases because of concentration quenching effect. Under the excitation at 395 nm corresponding to ⁷F₀ → ⁵L₆ transition of Eu³⁺, only characteristic Eu³⁺ emission bands can be observed. The results of this work suggest that tunable luminescence can be obtained for Eu³⁺ doped NaLa(WO₄)₂ phosphors by changing Eu³⁺ concentration and excitation wavelength.     

Structural and luminescent properties of Eu3+-doped GdSrAl3O7 nanophosphor

Eu³⁺-doped GdSrAl₃O₇ nanophosphor with promising luminescent properties has been synthesized by low-temperature solution combustion synthesis. The structural properties examined by X-ray diffractometer, scanning electron microscopy, and transmission electron microscopy showed that pure tetragonal GdSrAl₃O₇: Eu³⁺ red nanophosphor having narrow size distribution in 50–55 nm range could be readily obtained at low temperature 550 °C. The photoluminescent excitation and emission spectra, life time, and concentration effect were studied in detail. Under excitation at 266 nm, Eu³⁺-doped GdSrAl₃O₇ nanophosphor revealed weak green emission and strong red emission attributed to ⁵D₁ → ⁷F_1–2 and ⁵D₀ → ⁷F_0–3 transitions of Eu³⁺ ion, respectively in the region of 525–700 nm. The red emission from ⁵D₀ → ⁷F₂ transition at 616 nm exhibits the highest intensity under the optimized concentration of 10 mol% after which the quenching mechanism became relevant. Quenching behavior of the europium in the GdSrAl₃O₇ host was explained by nonradiative cross-relaxation phenomenon. Moreover, Eu³⁺-doped GdSrAl₃O₇ nanophosphor can generate light from orange to deeper red by properly tuning the concentration of europium ions based on the energy transfer principle.     

Synthesis and luminescence properties of LaOCl:Eu3+ nanostructures via the combination of electrospinning with chlorination technique

LaOCl:Eu³⁺ nanofibers, nanobelts and nanotubes were prepared by electrospinning combined with a double-crucible chlorination technique using NH₄Cl as chlorinating agent. Different morphologies of LaOCl:Eu³⁺ were obtained via adjusting some of the electrospun parameters. X-ray powder diffraction analysis indicated that LaOCl:Eu³⁺ nanostructures were tetragonal with space group P4/nmm. Scanning electron microscope analysis and histograms revealed that diameters LaOCl:Eu³⁺ nanofibers and nanotubes, and the width of LaOCl:Eu³⁺ nanobelts were respectively 198.64 ± 15.07, 168.86 ± 24.70 and 2.103 ± 0.3345 μm under the 95 % confidence level. Transmission electron microscope observation showed that as-obtained LaOCl:Eu³⁺ nanotubes were hollow-centered structure. Photoluminescence (PL) analysis manifested that the LaOCl:Eu³⁺ with different morphologies emitted the predominant emission peaks at 616 and 618 nm originating from the transition ⁵D₀ → ⁷F₂ of Eu³⁺ ions under the excitation of 283-nm ultraviolet light. It was found that the optimum molar ratio of Eu³⁺/(La³⁺+Eu³⁺) ions was 5 %. LaOCl:Eu³⁺ nanobelts exhibited the strongest PL intensity of the three morphologies under the same doping concentration. CIE analysis demonstrated that color-tuned luminescence can be obtained by changing doping concentration of Eu³⁺ ions and morphologies of nanomaterials, which could be applied in the fields of optical telecommunication and optoelectronic devices. The possible formation mechanisms of LaOCl:Eu³⁺ nanofibers, nanobelts and nanotubes were also proposed.     

Ca2SiO4:Ln (Ln = Ce3+, Eu2+, Sm3+) tricolor emission phosphors and their application for near-UV white light-emitting diode

Tricolor emission Ca₂SiO₄:Ln (Ln = Ce³⁺, Eu²⁺, Sm³⁺) phosphors were synthesized by the conventional solid-state reaction method, and their photoluminescence properties were investigated. Ce³⁺-, Eu²⁺-, or Sm³⁺-doped Ca₂SiO₄ phosphors showed typical blue, green, or red luminescence in the CIE1931 chromaticity diagram, respectively. In addition, the luminescence efficiency of the tricolor emission Ca₂SiO₄:Ln (Ln = Ce³⁺, Eu²⁺, Sm³⁺) phosphors was evaluated. A series of white light-emitting diode (LED) prototypes were fabricated by combining near-UV LED chip and the as-prepared tricolor emission phosphors with various ratios in weight. White LED prototypes with tunable correlated color temperature and color-rendering index values were realized by controlling the amount of phosphors. The presented results indicated the potential application of Ca₂SiO₄:Ln (Ln = Ce³⁺, Eu²⁺, Sm³⁺) phosphors in near-UV white LED.     

Effects of Eu3+ ions on the morphology and luminescence properties of hydroxyapatite nanoparticles synthesized by one-step hydrothermal method

In the present investigation, we have demonstrated the synthesis of sphere shaped HA phosphors by a simple one-step hydrothermal method, and the structural, morphological, textural and optical properties were characterized by XRD, TEM, XPS, ICP and PL spectroscopy. Results showed that the crystal size and the ratio of length to radius of Eu³⁺-doped HA particles decreased with the increasing of Eu³⁺doped concentration, and its PL emission intensities increased with the increase of Eu³⁺doped concentration. When the Eu³⁺ amount was 7.5 at.%, the HA particle showed sphere shape, and the actual doping concentration and the PL emission intensities reach the maximum. This indicated that sphere shaped HA phosphors can be obtained by adjusting the Eu³⁺ doping concentration without adding any other reagent. And it also indicated that the PL emission intensities were mainly dependent on the Eu³⁺ doped concentration, and the effect of morphology was very little.     

Influence of the Eu3+ dosage concentration on luminescence properties of YPO4:Eu3+ microspheres

In this study, YPO₄:Eu³⁺ microspheres with different Eu³⁺ dosage concentration were fabricated by a facile hydrothermal route at 200 °C for 10 h in the presence of citric acid. The YPO₄:Eu³⁺ samples were characterized by X-ray powder diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), and luminescence spectroscopy. The XRD results reveal that the YPO₄:Eu³⁺ samples presented a tetragonal structure. The TEM and SEM observations demonstrate that the YPO₄:Eu³⁺ samples with uniform sphere-like morphologies can be obtained at 200 °C for 10 h. The sizes of samples are in the range of 2–2.2 μm. The room temperature luminescence properties of YPO₄:Eu³⁺ samples were studied using an excitation wavelength of 227 nm. The emission spectrum displays the bands associated to the ⁵D₀ → ⁷F_J (J = 1, 2 and 4) electronic transitions characteristics of the Eu³⁺ cations at different positions. The influence of Eu³⁺ dosage concentration on luminescence properties of YPO₄:Eu³⁺ microspheres were studied carefully.     

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.     

Luminescence and crystallinity of flame-made Y2O3:Eu3+ nanoparticles

Cubic and/or monoclinic Y₂O₃:Eu³⁺ nanoparticles (10–50 nm) were made continuously without post-processing by single-step, flame spray pyrolysis (FSP). These particles were characterized by X-ray diffraction, nitrogen adsorption and transmission electron microscopy. Photoluminescence (PL) emission and time-resolved PL intensity decay were measured from these powders. The influence of particle size on PL was examined by annealing (at 700–1300°C for 10 h) as-prepared, initially monoclinic Y₂O₃:Eu³⁺ nanoparticles resulting in larger 0.025–1 μm, cubic Y₂O₃:Eu³⁺. The influence of europium (Eu³⁺) content (1–10 wt%) on sintering dynamics as well as optical properties of the resulting powders was investigated. Longer high-temperature particle residence time during FSP resulted in cubic nanoparticles with lower maximum PL intensity than measured by commercial micron-sized bulk Y₂O₃:Eu³⁺ phosphor powder. After annealing as-prepared 5 wt% Eu-doped Y₂O₃ particles at 900, 1100 and 1300°C for 10 h, the PL intensity increased as particle size increased and finally (at 1300°C) showed similar PL intensity as that of commercially available, bulk Y₂O₃:Eu³⁺ (5 μm particle size). Eu doping stabilized the monoclinic Y₂O₃ and shifted the monoclinic to cubic transition towards higher temperatures.     

Eu3+ concentration effect on luminescence properties of YAG:Eu3+ nanoparticles

Nanocrystalline Eu³⁺-doped YAG powders were prepared by modified Pechini method. The structural properties were investigated with XRD, SEM and Raman spectroscopy. XRD pattern indicated that the phase-pure YAG:Eu³⁺ crystallites were obtained without the formation of any other phases. Raman spectrum revealed good homogeneity and crystallinity of synthesized nanopowders. The luminescent properties were studied by measurement of excitation and emission spectra, quantum yields and decay curves. The effect of Eu³⁺ concentration on ⁵D₀ level lifetime was studied. The processes resulting in the relaxation of excited state (⁵D₀ level) were discussed and the probabilities of radiative and nonradiative processes were calculated using the model of f–f transition intensities. It was found that the observed shortening of ⁵D₀ level lifetime with Eu concentration is caused by increase of nonradiative process probability.     

Tunable luminescence properties and energy transfer of single-phase Ca<Subscript>4</Subscript>(PO<Subscript>4</Subscript>)<Subscript>2</Subscript>O: Dy<Superscript>3+</Superscript>, Eu<Superscript>2+</Superscript> multi-color phosphors for warm white light

The novel Ca_4?x(PO₄)₂O: xDy³⁺ and Ca_4?x?y(PO₄)₂O: xDy³⁺, yEu²⁺ multi-color phosphors were synthesized by traditional solid-state reaction. The crystal structure, particle morphology, photoluminescence properties and energy transfer process were investigated in detail. The X-ray diffraction (XRD) results demonstrate that the products showed pure monoclinic phase of Ca₄(PO₄)₂O when x < 0.1. The scanning electron microscopy (SEM) indicated that the phosphors were grain-like morphologies with diameters of ~ 3.7–7.0 μm. Under excitation of 345 nm, Dy³⁺-doped Ca₄(PO₄)₂O phosphors showed multi-color emission bands at 410, 481 and 580 nm originated from oxygen vacancies and Dy³⁺. Interestingly, Ca₄(PO₄)₂O: Dy³⁺, Eu²⁺ phosphors exhibited blue emission band at 481 nm and broad emission band from 530 to 670 nm covering green to red regions. The energy transfer process from Dy³⁺ to Eu²⁺ was observed for the co-doped samples, and the energy transfer efficiency reached to 60% when Eu²⁺ molar concentration was 8%. In particular, warm/cool/day white light with adjustable CCT (2800–6700 K) and high CRI (R_a > 85) can be obtained by changing the Eu²⁺ co-doping contents in Ca₄(PO₄)₂O: Dy³⁺, Eu²⁺ phosphors. The optimized Ca_3.952(PO₄)₂O: 0.04Dy³⁺, 0.008Eu²⁺ phosphor can achieve the typical white light with CCT of 4735 K and CRI of 87.     

Synthesis and annealing effects on the optical spectroscopy properties of red-emitting Gd(P<Subscript>0.5</Subscript>V<Subscript>0.5</Subscript>)O<Subscript>4</Subscript>: x at.% Eu<Superscript>3+</Superscript>

In this work, Gd(P_0.5V_0.5)O₄: x at.% Eu³⁺ phosphors with different dopant concentrations (x?=?1, 3, 5, 6, 7, 9) were synthesized through chemical coprecipitation method. The phosphors were characterized by XRD, SEM, infrared spectroscopy, photoluminescence excitation, emission spectra and CIE. The results of XRD indicate that the obtained phosphors have the tetragonal phase structure. Eu³⁺ emission transitions arise mainly from the ⁵D₀ level to the ⁷F_J (J?=?0, 1, 2, 3, 4) manifolds. The emission intensity and crystalline of Gd(P_0.5V_0.5)O₄:x at% Eu³⁺ powders are increasing with annealing temperature at 600, 800, 1000, 1100, and 1200 °C, respectively. The introduction of VO₄^3? can broaden the range of UV excitation spectrum wavelength and enhance the transition between ⁵D₀ → ⁷F₁ to ⁵D₀ → ⁷F₂ for long wavelength emission. And the most dominant emission peak of Eu³⁺ for ⁵D₀ → ⁷F₂ transition is closer to pure red light at 622 nm. The maximum emission intensity of the phosphors is the concentration of 6 at.% Eu³⁺ because of the distance of the neighbor Eu³⁺ ions reaching a certain critical value and the influence of multipolar interaction. Compared to commercial phosphors Y₂O₃:Eu³⁺ and (Y,Gd)BO₃:Eu³⁺, our work yielded a longer wavelength red light emission intensity and a higher proportion of red light to orange light. All our results indicate that color purity of this phosphor turns it into a promising red phosphor in ultraviolet-pumped light-emitting diodes.     

Molten salt synthesis,characterization, and luminescence of SrWO4, SrWO4:Tb3+ and SrWO4:Eu3+ powders

SrWO₄, SrWO₄:Tb³⁺, and SrWO₄:Eu³⁺ powders were synthesized by a method of molten salt. XRD patterns showed that the synthesized powders have a pure tetragonal scheelite structure without the presence of deleterious phases. Scanning electron microscopy images show that powders are in the range of 20–35 nm. The emission spectrum of SrWO₄ shows the emission peak in the blue spectral region. The excitation spectra of SrWO₄:Tb³⁺ and SrWO₄:Eu³⁺ show the energy transfer from WO₄ ^2? group to Tb³⁺ and Eu³⁺ ions with a high efficiency. The emission spectrum of SrWO₄:Tb³⁺ shows the green emission at 545 nm corresponding to the ⁵D₄ → ⁷F₅ transition of Tb³⁺. The emission spectrum of SrWO₄:Eu³⁺ shows the red emission located at 612 nm corresponding to the ⁵D₀ → ⁷F₂ transition of Eu³⁺. The asymmetry ratio of SrWO₄:Eu³⁺ is found to be 5.54, which indicates that the Eu³⁺ ions are located in a lower symmetric site.     

Photoluminescence properties of a novel red-emitting phosphor Ba<Subscript>2</Subscript>LaV<Subscript>3</Subscript>O<Subscript>11</Subscript>:Eu<Superscript>3+</Superscript>

Ba₂LaV₃O₁₁:Eu³⁺ phosphors were firstly synthesized by the traditional solid-state reaction method at 1100 °C. Their luminescence properties were investigated by photoluminescence excitation and emission spectra. The excitation spectrum shows a broad band centered at about 275 nm in the region from 200 to 370 nm, which is attributed to an overlap of the charge transfer transitions of O^2??→?V⁵⁺ and O^2??→?Eu³⁺. The phosphors exhibit the red emissions of Eu³⁺ and the emission intensity ratio of ⁵D₀?→?⁷F₂ to ⁵D₀?→?⁷F₁ is dependent on the Eu³⁺ concentration due to an environment change about Eu³⁺ ions. Concentration quenching occurs at 30 mol% in the phosphors and exchange interaction is its main mechanism. Ba₂LaV₃O₁₁:Eu³⁺ displays tunable CIE color coordinates from yellow orange to red depended on Eu³⁺ content, which may have a potential application for illuminating and display devices.     

Uniform lanthanide-doped Y2O3 hollow microspheres: Controlled synthesis and luminescence properties

Lanthanide-doped uniform pure cubic phase Y₂O₃ hollow microspheres have been successfully synthesized via a facile, high yield urea-based coprecipitation route with assistant of carbon spheres templates. The diameter and shell thickness of the microspheres can be manipulated by adjusting carbon sphere templates. Under a 980 nm excitation, Yb³⁺/Er³⁺, Er³⁺, Yb³⁺/Tm³⁺-doped Y₂O₃ hollow microspheres emit bright upconversion red, green, blue light with high purity, respectively, while Eu³⁺, Eu³⁺/Tb³⁺-doped Y₂O₃ hollow microspheres exhibit intense downconversion red light under the excitation of 254 nm ultraviolet light. Especially, the 610 nm emission intensity of Eu³⁺ in the Eu³⁺/Tb³⁺-codoped Y₂O₃ hollow microspheres is almost 5 times of that in the Y₂O₃:Eu³⁺ hollow microspheres indicating the occurring of the energy transfer from Tb³⁺ to Eu³⁺ ions.     

Fabrication and luminescence properties of YF3:Eu3+ hollow nanofibers via coaxial electrospinning combined with fluorination technique

Polyvinyl pyrrolidone (PVP)–PVP/[Y(NO₃)₃ + Eu(NO₃)₃] core–sheath composite nanofibers were prepared by coaxial electrospinning, and then Y₂O₃:Eu³⁺ hollow nanofibers were synthesized by calcination of the as-prepared composite nanofibers. For the first time, YF₃:Eu³⁺ hollow nanofibers were successfully fabricated by fluorination of the Y₂O₃:Eu³⁺ hollow nanofibers via a double-crucible method using NH₄HF₂ as fluorinating agent. The morphology and properties of the products were investigated in detail by X-ray diffraction, scanning electron microscope (SEM), transmission electron microscope (TEM), and fluorescence spectrometer. YF₃:Eu³⁺ hollow nanofibers were pure orthorhombic phase with space group Pnma and were hollow-centered structure with the mean diameter of 211 ± 29 nm. Fluorescence emission peaks of Eu³⁺ in the YF₃:Eu³⁺ hollow nanofibers were observed and assigned to the energy levels transitions of ⁵D₀ → ⁷F₁ (587 and 593 nm), ⁵D₀ → ⁷F₂ (615 and 620 nm), and the ⁵D₀ → ⁷F₁ hypersensitive transition at 593 nm was the dominant emission peak. Moreover, the emitting colors of YF₃:Eu³⁺ hollow nanofibers were located in the red region in CIE chromaticity coordinates diagram. The luminescent intensity of YF₃:Eu³⁺ hollow nanofibers was increased remarkably with the increasing doping concentration of Eu³⁺ ions and reached a maximum at 7 mol% of Eu³⁺. This preparation technique could be applied to prepare other rare earth fluoride hollow nanofibers.     

Photoluminescence of cubic BN doped with europium and codoped with europium and chromium

We have prepared cubic boron nitride samples doped with europium and codoped with europium and chromium. Their red photoluminescence is due to Eu³⁺ and Eu³⁺-Cr³⁺ electronic transitions involving Eu³⁺ in a noncentrosymmetric position in a field of cubic symmetry. Chromium is shown to have a positive effect on the incorporation of Eu³⁺ into lattice sites of c-BN. The photoluminescence spectrum of polycrystalline c-BN codoped with Eu³⁺ and Cr³⁺ is a combination of the spectra of Eu³⁺ in fields of cubic and monoclinic symmetries, the latter spectrum being blue-shifted relative to the spectrum of Eu³⁺-doped microcrystalline powder. The c-BN materials prepared in this study can be used as red phosphors and light emitters possessing high thermal stability, radiation hardness, and chemical resistance.     

Green synthesis of white-light-emitting ZnSe:Eu<Superscript>2+</Superscript>, Mn<Superscript>2+</Superscript> quantum dots in an aqueous solution

High-quality ZnSe:Eu, Mn quantum dots (QDs) with white light emitting were synthesized via a green preparation method in an aqueous solution using thioglycolic acid as a stabilizing agent. The composition of the QDs could be flexibly controlled by varying the amount of Eu or Mn cation. The effects of reflux time and Eu²⁺ ion dopant concentration on the luminescence properties were systematically investigated. The obtained QDs were characterized by photoluminescence spectrometry, X-ray powder diffraction, and high-resolution transmission electron microscopy. The proposed method formed cubic ZnSe:Mn²⁺, Eu²⁺ QDs with the maximum emission peak at 460 and 580 nm. In the optimal condition, the quantum yields of ZnSe:Mn²⁺, Eu²⁺ QDs could reach 27.68%. The CIE color coordinates were (0.328, 0.334), which agreed with those of pure white light (0.33, 0.33). The results verified that the ZnSe:Mn²⁺, Eu²⁺ QDs exhibited potential in light-emitting diode applications.