Synthesis and luminescence characterization of Pr3+, Gd3+ co-doped SrF2 transparent ceramics

Pr³⁺, Gd³⁺ co-doped SrF₂ transparent ceramic, as the potential material for visible luminescent applications, was prepared by hot-pressing of precursor nanopowders. The microstructure, phase compositions, and in-line transmittance, as well as the photoluminescence properties were investigated systematically. Highly optical quality Pr,Gd:SrF₂ transparent ceramic with nearly pore-free microstructure was obtained at 800°C for 1.5 hours. The average in-line transmittance of the x at.% Pr, 6 at.% Gd:SrF₂ (x = 0.2, 0.5, 1.0, 2.0) transparent ceramics reached to 87.3 % in the infrared region. The photoluminescence spectra presented intense visible light emissions under the excitation of 444 nm, the main intrinsic emission bands located at 483 and 605 nm, which were attributed to the transitions of Pr³⁺: ³P₀ → ³H₄ and ¹D₂ → ³H₄, respectively. With the co-doping of Gd³⁺ ions, the emission intensity of the Pr:SrF₂ transparent ceramic was greatly enhanced. All the emission bands of x at.% Pr, 6 at.% Gd:SrF₂ transparent ceramics exhibited the highest luminescence intensity with the 1.0 at.% Pr³⁺ doping concentrations, whereas the lifetimes decreased dramatically with the Pr³⁺ doping contents increasing from 0.2 to 2.0 at.% due to its intense concentration quenching effect. The 1 at.% Pr, 6 at.% Gd:SrF₂ transparent ceramic is a promising material for visible luminescent device applications.     

Preparation and characterizations of Pr3+:CaF2 transparent ceramics with different doping concentrations

0.2–5.0?at% Pr³⁺-doped CaF₂ transparent ceramics were fabricated by hot-pressed processing for the first time. The phase compositions, microstructure and optical characteristics of the presented transparent ceramics were examined systematically. The average in-line transmittance of Pr:CaF₂ transparent ceramics (2.0?mm thick) with high Pr³⁺ doping concentrations (1.0–5.0?at%) exceeds 86% at the wavelength of 1200?nm. The absorption spectrum manifests that the prepared Pr:CaF₂ transparent ceramics contain some absorption peaks overlapped with emission bands of the commercial InGaN laser diodes. Further, a detailed investigation on the visible emission properties as a function of Pr³⁺ concentrations in CaF₂ transparent ceramics was reported. The emission spectra presented two main characteristic peaks at 496?nm (bluish green) and 656?nm (red) corresponded to the transitions of ³P₀→³H₄ and ³P₀→³F₂ for Pr³⁺ activator ions. With the increase of the Pr³⁺ doping concentrations, the emission intensity and decay lifetimes decreased generally attributed to the concentration quenching effect. Details on energy transfer mechanism of Pr³⁺ in CaF₂ transparent ceramics were demonstrated and discussed.     

Effects of Gd3+ substitution on the structure,photoluminescence, scintillation,and thermometric features of Pr3+:Lu2Zr2O7 phosphors

In this study, it is shown how the photoluminescence, scintillation, and optical thermometric properties are managed via the introduction of Gd³⁺ ions into Pr³⁺:Lu₂Zr₂O₇. Raman spectra validate that partial replacement of Lu³⁺ with Gd³⁺ can promote the phase transition of Lu₂Zr₂O₇ host from the defective fluorite structure to the ordered pyrochlore one. Upon 289 nm excitation, all the samples emit the 483 (³P₀ → ³H₄), 581 (¹D₂ → ³H₄), 611 (³P₀ → ³H₆), 636 (³P₀ → ³F₂), and 714 nm (³P₀ → ³F₄) emissions from Pr³⁺ ions, which are enhanced with the addition of Gd³⁺ ions due to the modification of crystal structure. Dissimilarly, the X-ray excited luminescence spectra consist of a strong emission located at 314 nm from Gd³⁺ ions (⁶P_7/2 → ⁸S_7/2), together with the typical emissions from Pr³⁺ ions, which exhibit different dependences on the Gd³⁺ concentration. When the luminescence intensity ratio between the ³P₀ → ³H₆ (611 nm) and ¹D₂ → ³H₄ (581 nm) transitions is selected for temperature sensing, Pr³⁺:(Lu_0.75Gd_0.25)₂Zr₂O₇ shows the optimal relative sensing sensitivity of 0.78% K⁻¹ at 303 K, which is higher than that of the Gd³⁺-free sample. Therefore, the developed Pr³⁺:(Lu, Gd)₂Zr₂O₇ phosphors have the applicative potential for optical thermometry, X-ray detection, and photodynamic therapy.     

Photoluminescent and scintillant properties of highly transparent [(Y1-xGdx)0.99Dy0.01]2O3 (x = 0 and 0.4) ceramics

High-optical-quality ternary [(Y_1-xGd_x)_0.99Dy_0.01]₂O₃ (x = 0 and 0.4) ceramics were successfully fabricated by vacuum sintering with in-line transmittances of 71.4%-75.1% at 574 nm, the wavelength of Dy³⁺ emission (the ⁴F_9/2 → ⁶H_13/2 transition). Substitution of Gd³⁺ for Y³⁺ significantly affected the photoluminescent and scintillant properties of the ceramics. Gd³⁺ addition effectively increased lattice parameters and theoretical densities of the ceramic samples; this contributed to enhanced X-ray absorption coefficients. Both [(Y_1-xGd_x)_0.99Dy_0.01]₂O₃ (x = 0 and 0.4) ceramics displayed typical Dy³⁺ emissions from ⁴F_9/2 → ⁶H_J (J = 15/2, 13/2, 11/2) transitions under UV and X-ray irradiations. By incorporating Gd³⁺ into the lattice, a stronger excitation peak of Gd³⁺ due to internal f-f transitions relative to Dy³⁺ was observed at 276 nm; subsequent ceramics obtained a sharper PL intensity and a warmer hue via effective energy transfer from Gd³⁺ to Dy³⁺. Using a Gd³⁺ dopant generally reduces the total photoluminescence/photoluminescence excitation intensities and light output; it also delays the lifetime and afterglow of the transparent ceramics.     

The microstructure and magnetic properties of Ca2+ ion doped GdCrO3

In this paper, the crystal structure, vacancy defect, local electron density and magnetic properties of Gd_1-xCa_xCrO₃ (0 ≤ x ≤ 0.3) polycrystalline samples were investigated systematically. The crystal structural analyses show that all the samples are orthorhombic phase and a structural distortion happens around x = 0.3. Due to the formation of Cr⁴⁺ ions, both the lattice constant and the Cr–O bond length decrease. The results of positron annihilation spectrum reveals that the vacancy defect concentration increases and the local electron structure changes with the introduction of Ca²⁺ ions. The field-cooled (FC) and zero-field cooled (ZFC) curves of Gd_1-xCa_xCrO₃ samples measured under H = 100 Oe exhibits negative magnetization characteristics due to the interaction between Gd³⁺ and Cr³⁺ ions, and the magnetism can be affected by the structural distortion.     

Reversible luminescence modulation and temperature-sensing properties of Pr3+/Yb3+ codoped K0.5Na0.5NbO3 ceramics

In this work, we have prepared a novel (K_0.5Na_0.5)_0.99-xPr_xYb_0.01NbO₃ (abbreviated as KNN:xPr³⁺/0.01Yb³⁺, x = 0.0006, 0.0008, 0.001, 0.002, 0.003, and 0.004) ceramics, which possess visible UC emissions, photochromic (PC) and optical thermometric properties. Under the excitation of a 980-nm diode laser, all the samples show the featured emissions of Pr³⁺ ions and the UC emission intensity is greatly dependent on the Pr³⁺ doping content. The optimal UC luminescence intensity is obtained at x = 0.001. All the prepared samples show a strong PC reaction, and a large luminescence quenching degree (ΔR_t) of 74.94% is found. The optical thermometric properties of both the irradiated and unirradiated KNN:0.001Pr³⁺/0.01Yb³⁺ ceramics in the temperature range of 123-573 K have been investigated via measuring the temperature-dependent UC emission spectra of green emissions, which originate from the two ³P₁ and ³P₀ thermally coupled levels. It has been found that the prepared samples have both excellent PC behaviors and temperature-sensing performances. These results suggest that the KNN:xPr³⁺/0.01Yb³⁺ ceramics are promising candidates for the applications in PC reaction and thermometers.     

Linear correlation of crystal structure and spectral properties of Nd3+ in Ca1-xSrxF2 mixed crystals

Crystal structure and the optical spectral properties of 0.5 at.% Nd³⁺, 5 at.% Gd³⁺-codoped Ca_1-xSr_xF₂ (0 ≤ x≤1) crystals grown by the temperature gradient technique (TGT) were investigated. The linear variations of the crystal structure and spectral parameters as a function of Sr²⁺ proportion (x) were observed and correlated with each other. The results indicated that Sr²⁺ ions introduced as matrix-substituted ions could regulate the crystal structures and the spectroscopic properties.     

Fabrication and phase transition of uranium-doped LaxGd2−xZr2O7 transparent ceramics: A prospective neutron detection material

Via vacuum sintering, 2 mol% uranium-doped La_xGd_2−xZr₂O₇ (x = 2, 1.6, 1, and 0.4) transparent ceramics with Ca²⁺ as charge compensator was first fabricated by solid-state reaction. X-ray diffraction results of as-prepared powders and ceramic samples demonstrate that the phase transition from defective fluorite to pyrochlore occurs with the increase of x. Optical in-line transmittance spectrum shows that four ceramic samples have good in-line transmittance (nearly 80% from 700 to 2200 nm), especially the U:La_1.6Gd_0.4Zr₂O₇ ceramics. The cut-off wavelength of four U-doped transparent ceramics shifted from 250 to near 460 nm, and it is believed that such phenomenon is related to the stable existence form of uranium in ceramics lattices. Observing the excitation emission spectra, the main excitation peaks of four ceramic samples are located at 458 nm, and the main emission peaks are located around 513 nm. In addition, there are low-intensity emission peaks around 520, 537, and 566 nm, and the related explanation is given in combination with the U⁶⁺ ion energy level diagram. Thus, uranium-doped La_xGd_2−xZr₂O₇ transparent ceramics have potential for novel neutron detection materials.     

Influence of Gd2O3 on the microstructure and properties of transparent MgAl2O4: Cr3+ ceramic

In this work, MgAl₂O₄: Cr³⁺ transparent ceramics have been synthesized by the hot press sintering techniques, and the effect of the sintering aid Gd₂O₃ and its content on the densification, microstructure, and optical, photoluminescence was studied and discussed. The relative density reached 99.29% with 0.8 wt% Gd₂O₃ as a sintering aid, and the optical transmittance at 686 nm and 1446 nm were approximately 76%. As Gd₂O₃ content continued to increase, the grain size of the ceramics became smaller and uniform, accompanied by some pores with the size of ～1 μm. The ceramics with 4.0 wt% Gd₂O₃ showed a higher transmittance, of 82% at 1446 nm. Additionally, Gd₂O₃ was helpful for Cr³⁺ in the sites of octahedral symmetry, which increased the quantum yield. The quantum yield of MgAl₂O₄: Cr³⁺ with 0.8 wt% Gd₂O₃ was about 0.175, which was 36% higher than that of ceramic without Gd₂O₃. In short, the sintering aid Gd₂O₃ not only contributed to improving the densification, homogenizing the grain size, and heightening the optical transmittance but also enhanced the quantum yield of Cr³⁺.     

Spectral Properties of Pr3+‐Doped Transparent‐Glass‐Ceramic Containing Ca5(PO4)3F Nanocrystals

A Pr³⁺‐doped transparent oxyfluoride glass‐ceramic containing Ca₅(PO₄)₃F nanocrystals was prepared by melt quenching and subsequent thermal treatment. The crystallization phase and morphology of the Ca₅(PO₄)₃F nanocrystals were investigated by X‐ray diffraction and transmission electron microscope, respectively. The volume fraction of the Ca₅(PO₄)₃F nanocrystals in the glass‐ceramic is about 10% and the fraction of Pr³⁺ ions incorporated into the Ca₅(PO₄)₃F nanocrystals is about 22%. The peak absorption cross sections at 435 and 574 nm increase up to 128% and 132% after crystallization, respectively. The peak stimulated emission cross sections of the ³P₀→³H₄ blue laser channel and ³P₀→³F₂ red laser channel for the glass‐ceramic are 4.95 × 10^?20 and 29.8 × 10^?20 cm², respectively. The spectral properties indicate that the glass‐ceramic is a potential visible laser material.     

Effects of Gd Substitution on Sintering and Optical Properties of Highly Transparent (Y0.95−xGdxEu0.05)2O3 Ceramics

Highly transparent (Y_0.95?xGd_xEu_0.05)₂O₃ (x = 0.15–0.55) ceramics have been fabricated by vacuum sintering at the relatively low temperature of 1700°C for 4 h with the in‐line transmittances of 73.6%–79.5% at the Eu³⁺ emission wavelength of 613 nm (~91.9%–99.3% of the theoretical transmittance of Y_1.34Gd_0.6Eu_0.06O₃ single crystal), whereas the x = 0.65 ceramic undergoes a phase transformation at 1650°C and has a transparency of 53.4% at the lower sintering temperature of 1625°C. The effects of Gd³⁺ substitution for Y³⁺ on the particle characteristics, sintering kinetics, and optical performances of the materials were systematically studied. The results show that (1) calcining the layered rare‐earth hydroxide precursors of the ternary Y–Gd–Eu system yielded rounded oxide particles with greatly reduced hard agglomeration and the particle/crystallite size slightly decreases along with increasing Gd³⁺ incorporation; (2) in the temperature range 1100°C–1480°C, the sintering kinetics of (Y_0.95?xGd_xEu_0.05)₂O₃ is mainly controlled by grain‐boundary diffusion with similar activation energies of ~230 kJ/mol; (3) Gd³⁺ addition promotes grain growth and densification in the temperature range 1100°C–1400°C; (4) the bandgap energies of the (Y_0.95?xGd_xEu_0.05)₂O₃ ceramics generally decrease with increasing x; however, they are much lower than those of the oxide powders; (5) both the oxide powders and the transparent ceramics exhibit the typical red emission of Eu³⁺ at ~613 nm (the ⁵D₀→⁷F₂ transition) under charge transfer (CT) excitation. Gd³⁺ incorporation enhances the photoluminescence and shortens the fluorescence lifetime of Eu³⁺.     

Investigation on Crystallization and Optical Properties of Ca1−xLaxF2+x Glass‐Ceramics

Transparent oxyfluoride glass‐ceramics containing Er³⁺, Yb³⁺:Ca_1?xLa_xF_2+x nanocrystals, which may have potential applications in the fields of solid‐state laser and luminescence, were prepared. Crystallization of Ca_1?xLa_xF_2+x and behavior of Yb³⁺ and Er³⁺ during the heat treatment was investigated. Results showed that alumina content had a significant effect on crystallization of Ca_1?xLa_xF_2+x in the SiO₂–Al₂O₃–CaF₂–LaF₃ system. Due to the size of phase‐separated areas, the size of the crystals during the heat treatment did not change significantly. After crystallization of Ca_1?xLa_xF_2+x in the glass, the majority of Er³⁺ ions incorporated into the Ca_1?xLa_xF_2+x crystals during the heat‐treatment process. Time‐resolved luminescence of Er³⁺ ions in the samples around 842 nm showed that the solubility of Er³⁺ ions in Ca_1?xLa_xF₃ crystals is higher than pure CaF₂ crystals. The glass undergoes an enormous phase separation, which keeps the Yb³⁺ ions within the other separated phase. Therefore, only at high temperatures (790°C) or with a long heat‐treatment time (72 h), there is a possibility for Yb³⁺ ions to be incorporated into the fluorine phase.     

Dy3+/Ce3+ Codoped YAG Transparent Ceramics for Single‐Composition Tunable White‐Light Phosphor

Superior optical, thermal, and mechanical properties of transparent ceramics are very important in the applications of solid lasers, solid‐state lighting, and transparent armors. Herein, a series of (Dy_0.03Ce_xY_0.97?x)₃Al₅O₁₂ transparent ceramics were fabricated using vacuum reactive sintering method. Importantly, these Dy³⁺/Ce³⁺ codoped yttrium aluminum garnet (YAG) transparent ceramics served as single‐composition tunable white‐light phosphors for UV‐LEDs is developed for the first time. By combining with commercially available UV‐LEDs directly, the optimal chromaticity coordinates and correlated color temperature (CCT) are (x = 0.33, y = 0.35) and 5609 K, respectively. Notably, the codoping of Ce³⁺ enhances the luminescent intensity of Dy³⁺ ions while excited at 327 nm. The emission color of YAG transparent ceramics can be tuned from white to yellow through energy transfer between Dy³⁺ and Ce³⁺. These new phosphors, possessing of pure CIE chromaticity and environmentally friendly nature, are promising for applications in white UV‐LEDs.     

Effect of Y3+-O2- partial substitution with Ca2+-F- on the luminescence enhancement of Y2Mo3O12:Sm3+ red-emitting phosphors

To improve the luminescence property of Sm³⁺ in Y₂Mo₃O₁₂, partial Ca²⁺-F^- co-substituted Y₂Mo₃O₁₂:Sm³⁺ phosphor, namely Y_2-xCa_xMo₃O_12-xF_x:Sm³⁺, was prepared using a solid-state method. The effect of introducing Ca²⁺-F^- ion pairs on structure and luminescence properties of Y₂Mo₃O₁₂:Sm³⁺ was studied in depth. XRD patterns not only manifested that all as-prepared Y_2-xCa_xMo₃O_12-xF_x:Sm³⁺ samples had standard Y₂Mo₃O₁₂ structure, but also indicated the introduction of Ca²⁺-F^- ion pairs did not cause the change of crystal structure. Under the near ultraviolet excitation of 404 nm, the emission peaks of Y₂Mo₃O₁₂:Sm³⁺ were located at 567 nm, 605 nm and 652 nm, respectively, resulting from the 4f→4f electron transitions of Sm³⁺ ions. Furthermore, the luminescence intensity of Sm³⁺ was obviously enhanced through the co-substitution of Y³⁺-O^2- ions with Ca²⁺-F^- ions in Y₂Mo₃O₁₂ structure, and the chromaticity coordinates moved towards red region, which due to the environmental effect of crystal field around Sm³⁺. Besides, the red LED device was manufactured for suitable chromaticity parameters. All results indicated that the as-prepared Y_1.84Ca_0.06Mo₃O_11.94F_0.06:0.10Sm³⁺ red-emitting phosphor could become a promising candidate for application of white light-emitting diodes and plant illumination.     

Laser excitation-activated self-propagating sintering of NaYbF4:Pr3+/Gd3+ white light microcrystal phosphors

We demonstrate that self-propagating sintering reaction could be activated and dramatically enhanced by laser excitation of ion dopants in the solid-state reactants. Near-resonant laser absorption and subsequent nonradiative decays make the solid-state reactants be sintered efficiently while ionic excitations catalyze self-propagating solid-state reactions. As a prototype demo, we synthesized white light upconversion phosphors NaYbF₄:Pr³⁺/Gd³⁺. A continuous-wave laser at 980 nm was used to populate Yb³⁺ ions in YbF₃ to excited level, which react with NaF to preform NaYbF₄ nuclei. The preformed nuclei enhanced laser excitation and energy transfer to those ions that could not be directly excited by the pump laser and thus enabled self-propagating solid-state sintering synthesis of NaYbF₄ microcrystals at quite low laser powers. Laser excitation of Yb³⁺ ions could also benefit facile rare-earth ion doping through activated self-propagating reactions. Gd³⁺ and Pr³⁺ ions were doped in NaYbF₄ by simply adding Gd³⁺ and Pr³⁺ ionic oxides or fluorides in the raw materials. In addition, Gd³⁺ ions doping in F⁻ anions ambient could transform the NaYbF₄ microcrystal phase from cubic to hexagonal and tune upconversion photoluminescence. This synthetic method can be widely applied to synthesize many other solid-state compounds, perovskite solar cells, photocatalysts, solid oxide fuel cells, and so forth.     

Structural,spectroscopic and thermal properties of hot-pressed Nd:(Ca0.94Gd0.06)F2.06 transparent ceramics

0.5–5.0?at.% Nd³⁺ doped (Ca_0.94Gd_0.06)F_2.06 transparent ceramics were fabricated by vacuum hot-pressing sintering. The structural, spectroscopic and thermal properties of Nd:(Ca_0.94Gd_0.06)F_2.06 transparent ceramics, as well as the influence of Nd³⁺ content on these properties were investigated. The as-fabricated ceramic samples exhibited high transparency and nearly pore-free microstructure. The absorption peaks located at 538?nm, 576?nm, 736?nm, 792?nm and 865?nm were attributed to the transitions from ground state to the excited states of Nd³⁺ ions, and the absorption coefficients increased linearly with Nd³⁺ content increasing. The emission band of the sample doped with 1?at.% Nd³⁺ concentration exhibited the highest emission intensity, while the lifetime decreased sharply with the increase of Nd³⁺ concentration. In addition, with Nd³⁺ content increasing from 0.5 to 5.0?at.%, the thermal expansivity coefficients increased slightly, while the thermal conductivity decreased from 4.21 to 2.36?W/m?K at room temperature.     

Effect of Gd Content on Luminescence Properties of Eu3+‐Doped La2−xGdxZr2O7 Transparent Ceramics

3 at.% Eu³⁺‐doped La_2?xGd_xZr₂O₇ (x = 0–2.0) transparent ceramics were fabricated by vacuum sintering. The effect of Gd content on crystal structure, in‐line transmittance, and luminescence property of the ceramics were investigated. The ceramics are all cubic pyrochlore structure with high transparency. The cut‐off edge of the transmittance curve of the ceramics varied with Gd content and was also affected by the annealing process. The luminescence intensity became stronger for the ceramics annealed in air. As Gd content increased, the energy band structure as well as the luminescence behavior of the ceramics was changed; in addition, the symmetry of the crystal lattice reduced, resulting in the shift of the strongest luminescence peak from 585 nm to around 630 nm.     

Synthesis and characterization of Ca3-xLaxCo4-yCuyO9+δ cathodes for intermediate temperature solid oxide fuel cells

The calcium cobaltite Ca_3-xLa_xCo_4-yCu_yO_9+δ with x and y = 0 and 0.1 were synthesized and the electrical, thermal, and catalytic behaviors for the oxygen reduction reaction (ORR) for use as air electrodes in intermediate-temperature solid oxide fuel cells (IT-SOFCs) were evaluated. X?ray diffraction confirms the Ca_3-xLa_xCo_4-yCu_yO_9+δ samples were crystallized in a monoclinic structure and scanning electron microscopic image shows lamella-like grain formation. Introduction of dopants decreases slightly the loss of lattice oxygen and thermal expansion co-efficient. The Ca_3-xLa_xCo_4-yCu_yO_9+δ samples exhibit good phase stability for long-term operation, thermal expansion, and chemical compatibility with the Ce_0.8Gd_0.2O_2-δ electrolyte. Among the studied samples, Ca_2.9La_0.1Co₄O_9+δ shows a maximum conductivity of 176 Scm^?1 at 800 °C. Although the doped samples exhibit a higher total electrical conductivity, an improved symmetrical cell performance is displayed by the undoped sample. Comparing the sintering temperatures, the composite cathode Ca₃Co₄O_9+δ + Ce_0.8Gd_0.2O_2-δ sintered at 800 °C exhibit the lowest area specific resistance of 0.154 Ω cm² at 800 °C in air. In the Ca_3-xLa_xCo_4-yCu_yO_9+δ + GDC composite cathodes, the charge-transfer process at high frequencies presents a major rate limiting step for the oxygen reduction reaction.     

Enhanced negative thermal expansion of (KMg)3+-substituted Fe2Mo3O12 ceramics

Herein, we report the solid-state synthesis of (KMg)_xFe_2-xMo₃O₁₂ (0 = x ≤ 1.5) ceramics. Phase composition, crystal structure, morphology, phase transition and thermal expansion behavior of the (KMg)_xFe_2-xMo₃O₁₂ ceramics were investigated by XRD, Raman, XPS, HRTEM, EDX, SEM, TMA and high-temperature XRD. Results indicate that (KMg)³⁺ dual-cations have successfully replaced Fe³⁺ in Fe₂Mo₃O₁₂ ceramics and single-phase monoclinic (KMg)_xFe_2-xMo₃O₁₂ ceramics were prepared for 0.25 = x ≤ 1. (KMg)³⁺ introduction can increase the density of (KMg)_xFe_2-xMo₃O₁₂ ceramics and effectively improve their negative thermal expansion (NTE) performance. In addition, the phase transition temperature (Tc) of Fe₂Mo₃O₁₂ was reduced from 508.1 °C to room temperature with the increase of (KMg)³⁺-substitution. Monoclinic KMgFeMo₃O₁₂ ceramics was observed to show stronger NTE in a wider temperature range of 30–700 °C for the first time. Its corresponding coefficient of thermal expansion (CTE) is as high as ?17.21 × 10^?6 °C^?1. The distortion of [FeO₆/MgO₆] polyhedra in (KMg)_xFe_2-xMo₃O₁₂ caused by (KMg)³⁺-substitution contributed to the stronger NTE.     

Study of Eu3+–Gd3+ co-doped Ba–Bi–B glasses for red-laser applications: Physical,structural, photoluminescence and time-resolved spectral characteristics

A series of Eu³⁺ and Eu³⁺/Gd³⁺ co-doped barium-bismuth-borate (Ba–Bi–B) glasses were prepared by melt-quench technique. And deliberated the physical, structural, and spectroscopic properties of all glasses and explored the energy transfer process from Gd³⁺ to Eu³⁺ ions. The density of glasses increased with increasing of Gd³⁺ concentration in co-doped glasses. Characteristics of steady-state and time-resolved photoluminescence (PL) of Eu-doped and Eu³⁺-Gd³⁺ co-doped glasses under different excitation wavelengths suggested the prospects of the investigated glass system for display device applications. PL spectrum displays a strong red emission peak centered at 612 nm due to the Eu³⁺: ⁵D₀→ ⁷F₂ transition. Less intense emissions centered at 577 nm (⁷F₀), 590 nm (⁷F₁), 651 nm (⁷F₃) and 700 nm (⁷F₄) are also observed from the radiative transitions of the excited state ⁵D₀ of Eu³⁺ions. The values of radiative parameters such as transition probability, branching ratios, and stimulated emission cross-sections were obtained from Judd–Ofelt theory analysis and indicated the aptness of the Ba–Bi–B glasses for optical devices. A 5-fold enhancement in the PL intensity was observed in 1.0 mol% Eu³⁺ and 3.0 mol% Gd³⁺ co-doped glass under λ_Exci. = 394 nm excitation. The calculated commission Internationale de l'eclairage color coordinates and correlated color temperature values show that the Ba–Bi–B glasses are useful for red-laser and display device applications.