The gadolinium effect on crystallization behavior and luminescence of β-NaYF4:Yb,Er phase

Single phase β-NaY_0.8-xGd_xYb_0.18Er_0.02F₄ nanoparticles with different concentrations of gadolinium ions were prepared via PVP-assisted solvothermal treating at 200°C (PVP- polyvinylpyrrolidone). With the increase in Gd³⁺ concentration, size of the nanoparticles decreased. The up-converting spectra recorded upon 980 nm irradiation showed the green (510-560 nm) and red (640-690 nm) emissions, due to ²H_11/2, ⁴S_3/2 → ⁴I_15/2 and ⁴F_9/2 → ⁴I_15/2 transitions, respectively. The strongest up-conversion luminescence was detected in 15 mol% Gd³⁺-doped nanoparticles obtained after 20 hours of solvothermal treating. With the rise of Gd³⁺ content up-conversion emission decreased due to increased defect concentration in the NaYF₄ matrix. Fourier transform infrared spectroscopy proved in situ generation of hydrophilic nanoparticles as a result of PVP ligands retention at the particle surface.     

Broadband near-infrared emission enhancement in K2Ga2Sn6O16:Cr3+ phosphor by electron-lattice coupling regulation

Cr³⁺-doped phosphors have recently gained attention for their application in broadband near-infrared phosphor-converted light-emitting diodes (pc-LEDs), but generally exhibit low efficiency. In this work, K₂Ga₂Sn₆O₁₆:Cr³⁺ (KGSO:Cr) phosphor was designed and synthesized. The experimental results show that the Cr³⁺-doped phosphor exhibited broadband emissivity in the range 650-1300 nm, with a full width at half maximum (FWHM) of approximately 220-230 nm excited by a wavelength of 450 nm. With the co-doping of Gd³⁺ ions, the internal quantum efficiency (IQE) of the KGSO:Cr phosphor increased from 34% to 48%. The Gd³⁺ ions acted neither as activators nor sensitizers, but to justify the crystal field environment for efficient Cr³⁺ ions broad emission. The Huang-Rhys factor decreased as the co-doping of Gd³⁺ ions increased, demonstrating that the nonradiative transitions were suppressed. An efficient strategy for enhancing the luminescence properties of Cr³⁺ ions is proposed for the first time. The Gd³⁺–co-doped KGSO:Cr phosphor is a promising candidate for broadband NIR pc-LEDs.     

Synthesis and characterization of Tb/Gd dual-doped multifunctional hydroxyapatite nanoparticles

Tb³⁺/Gd³⁺ dual-doped multifunctional hydroxyapatite (Tb³⁺/Gd³⁺-HAp) nanoparticles with magnetic and luminescent properties were prepared by the co-precipitation method using CaCl₂ and Na₂HPO₄·12H₂O as raw materials and CTAB as a template in alkaline conditions. The products were characterized by X-ray diffractometry (XRD), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM). Single hexagonal phase Tb³⁺/Gd³⁺-HAp nanoparticles were obtained by the co-precipitation method and the products were sphere-like morphology with particle sizes ranging from 40 to 100 nm. Crystallinity degree of the products decreased with the Tb³⁺/Gd³⁺ substitute increasing. Photoluminescence (PL) and magnetic properties of the products were also investigated. The results show Tb³⁺/Gd³⁺-HAp nanoparticles are endowed with strong luminescence at 544 nm and prominent paramagnetic behavior, allowing their potential applications in biological labeling. Gd³⁺ ions sensitize the ⁵D₄-⁷F₅ transition emission of Tb³⁺ ions in HAp nanoparticles, and the PL emission intensity increases along with increasing concentration of Gd³⁺ ions. Concentration quenching occurs when the Gd³⁺ concentration exceeds 10 mol%. The magnetization level of Tb³⁺/Gd³⁺-HAp increased steadily with the doping concentration of Gd³⁺ ions.     

Study on luminescence properties of co-doped nanoparticles Gd2O3:Tb3+, Eu3+ synthesized by polyol route

Spherical-like Tb³⁺ and Eu³⁺ co-doped Gd₂O₃ nanoparticles with a particle size around 5.5 nm were synthesized by a polyol route. The optimized luminescence property was obtained when 5 mol% Tb³⁺ and 2 mol% Eu³⁺ were co-doped. The influence of different polyalcohol solvents (DEG/PEG) on particle size and luminescence properties was investigated. The results show that the nanoparticles Gd₂O₃:5%Tb³⁺ prepared in PEG presented greater particle size (around 79 nm) and higher luminescence intensity.     

Perfectly transparent pore-free Nd3+-doped Sr9GdF21 polycrystalline ceramics elaborated from single-crystal ceramization

An Nd³⁺-doped Sr₉GdF₂₁ (SGF) transparent pore-free polycrystalline ceramic is produced by the ceramization of single crystals. The average transmittance (T_A) of the Nd³⁺-doped SGF ceramic (8-mm thick) is about 90.6% in the visible region and more than 92% in the near-IR region. The fracture toughness of the Nd³⁺-doped SGF ceramic is up to 1.28 MPa m^1/2, which is significantly higher than that of similar types of ceramics. Gd³⁺ ions, acting as both buffer ions and pinning ions, effectively improve the optical and mechanical properties of the SGF ceramic, implying that the sample is a promising candidate for high-power lasers. Moreover, the SGF ceramic shows a high mid- and far-infrared (up to 9 μm) transmittance, low phonon energy, and high density (ρ = 4.8466 g/cm³), which pave the way for a wide range of applications such as infrared windows, mid- and far-infrared lasers, scintillators, and in photonics.     

Gd3+ doping induced microstructural evolution and enhanced visible luminescence of Pr3+ activated calcium fluoride transparent ceramics

Transparent Pr³⁺ doped Ca_1-xGd_xF_2+x (x = 0, 0.01, 0.03, 0.06, 0.10, 0.15) polycrystalline ceramics with fine-grained microstructures were prepared by the hot-pressing method. The dependence of microstructure, optical transmittance, luminescence performances and mechanical properties on the Gd³⁺ concentrations for Pr³⁺:Ca_1-xGd_xF_2+x transparent ceramics were investigated. The Gd³⁺ ions show positive effects on the microhardness of Pr³⁺:Ca_1-xGd_xF_2+x transparent ceramics as a result of the decrease in the grain sizes. Excited by the Xenon lamp of 444 nm, typical visible emissions located at 484 nm, 598 nm and 642 nm were observed. Furthermore, the incorporation of Gd³⁺ ions can greatly enhance the photoluminescence performance owing to the improvement in the concentration quenching effect. The quenching concentration of Pr³⁺ ions in CaF₂ transparent ceramics increased to 1 at.% as a result of the positive effect of Gd³⁺ codoping. The energy transfer mechanism of Pr³⁺ in the Pr³⁺:Ca_1-xGd_xF_2+x transparent ceramics has been investigated and discussed.     

Ag nanoparticles-polypyrrole-carbon black/mesoporous TiO2 novel nanocomposite as ultrafast visible-light-driven photocatalyst

Effective design and fabrication of novel visible light-oriented photocatalysts is an existing challenging task that requires further dedicated efforts, and it has been always a main concern among the scientific community. This study deals with the design and fabrication of an extremely active and ultrafast ternary photocatalyst based on Ag nanoparticles, polypyrrole doped carbon black (PPy-C) and mesoporous TiO₂ (m-TiO₂). Sol-gel methodology along with sonication and photodeposition routes have been employed for the successful creation of the ternary framework. Ternary photocatalyst composed of uniform spherical titania nanoparticles (10–15 nm in size) perfectly intermingled with the polymeric linkage of PPy-C. Fruitful creation of unique trio photocatalyst between AgNPs, PPy-C and m-TiO₂ was confirmed by XPS and XRD. FTIR analysis further supports the development of nanocomposite photocatalyst. TEM analysis showed uniform spherical m-TiO₂ nanoparticles (10–15 nm in size) covered by PPy-C with compact nodes like appearance interlocked very well among each other. The newly developed Ag@PPy-C/m-TiO₂ ternary photocatalyst exhibited band gap energy in desired visible range of spectra. The photocatalytic efficiency for all created photocatalysts has been evaluated taking Imidacloprid (insecticide derivative) and methylene blue (MB) dye as target pollutants. The novel Ag@PPy-C/m-TiO₂ photocatalyst produced astonishing results with ultrafast removal of both Imidacloprid as well MB dye under visible light irradiation. The newly created ultrafast Ag@PPy-C/m-TiO₂ photocatalyst has removed 96.0% of the insecticide Imidacloprid in only 25 min with almost ? 2.65 times more efficient than bare m-TiO₂ towards the removal of insecticide derivative. The present report offers a highly encouraging and vastly talented Ag@PPy-C/m-TiO₂ ternary photocatalyst, enabling the ideal management of extremely lethal and notorious chemicals.     

Luminescence and structural properties of Gd2SiO5:Eu3+ phosphors synthesized from the modified solid state method

This paper reports the preparation of Eu³⁺ doped Gadolinium oxyorthosilicate (Gd₂SiO₅:Eu³⁺) phosphor with different concentration of Eu³⁺(0.1–2.5 mol%) using the modified solid state reaction method. The synthesis procedure of the Gd₂SiO₅:Eu³⁺phosphor using inorganic materials such as Gd₂O₃, silicon dioxide (SiO₂), europium oxide (Eu₂O₃) and boric acid (H₃BO₃) as flux is discussed in detail. The prepared phosphor samples were characterized by using X-Ray Diffraction (XRD), Field Emission Gun Scanning Electron Microscopy (FEGSEM), Transmission Electron Microscopy (TEM), Fourier Transform Infrared Spectroscopy (FTIR), Photoluminescence (PL) and Thermoluminescence (TL). The Commission Internationale de l′Eclairage(CIE) coordinates were also calculated. The PL emission was observed in the 350–630 nm range for the Gd₂SiO₅:Eu³⁺ phosphor. PL excitation peaks were observed at 266, 275, 312 and 395 nm while the emission peaks were observed at 380, 416, 437, 545, 579, 589, 607, 615 and 628 nm. The emission peak at 615 nm was the most intense peak for all the different Eu³⁺ concentration samples. From the XRD data, using the Scherrer's formula, the average crystallite size of the Gd₂SiO₅:Eu³⁺ phosphor was calculated to be 33 nm. TL was carried out for the phosphor after both UV and gamma irradiation. The TL response of the Gd₂SiO₅:Eu³⁺ phosphor for the two different radiations was compared and studied in detail. It was found that the present phosphor can acts as a single host for red emission (1.5 mol%) for display devices and light emitting diode (LED) and white light emission for Eu³⁺(0.1 mol%) and it might be used as a TL dosimetric material for gamma dose detection.     

Embedding Gd2O3 nanoparticles hydrothermally prepared in a Fe3O4 shell and surface modification with a dextrose bio capping agent

The present work describes a multi-stage processing method for the hydrothermal synthesis of gadolinium oxide (Gd₂O₃) nanoparticles and subsequent surface modification with iron oxide (Fe₃O₄) and dextrose. To prepare gadolinium oxide nanoparticles, gadolinium chloride was reacted with sodium hydroxide, and the resulting precipitate was autoclaved. Subsequently, the product was calcined. Afterward, Gd₂O₃ nanoparticles were coated with a Fe₃O₄ nanolayer synthesized via coprecipitation, and the resulting core-shell nanocomposites were encapsulated in a dextrose capping agent for enhanced biocompatibility. The effect of various Gd₂O₃ synthesis parameters on particle size, structure, and magnetic properties was then investigated. These parameters included preliminary precipitation temperature (25, 90 °C) and stirring speed (400, 1000 rpm), hydrothermal temperature (150 and 180 °C) and pressure (5 and 10 bar), and final calcination temperature (600 and 1000 °C). For the investigation of nanocomposites, X-ray diffraction (XRD), scanning and transmission electron microscopy, dynamic laser scattering (DLS), Fourier-Transform infrared spectroscopy (FTIR), and magnetometry (VSM) techniques were used, while the viability of colloidal samples was determined using the MTT-assay method. The results indicated that increasing the steering speed and temperature of the precipitation process and raising the calcination temperature reduced the size of Gd₂O₃ nanoparticles. Autoclave dehydration had no discernible effect on Gd₂O₃ nanoparticles. TEM and SEM images confirmed the core/shell structure of Gd₂O₃/Fe₃O₄. The shell thickness of 74–95 nm core nanoparticles was in the range of 30–40 nm. With a saturation magnetization of 3.4 emu/g, the nanoparticles exhibited paramagnetic behavior. The 48-h MTT assay demonstrated excellent biocompatibility up to 285 μg solid concentrations containing 24.5 μg [Fe] and 91.2 μg [Gd], with viability remaining greater than 50% at 400 μg solid concentration.     

Optical properties of gadolinia-doped cubic yttria stabilized zirconia single crystals

Cubic zirconia single crystals stabilized with yttria and doped with Gd₂O₃ (0.10–5.00 mol%) were prepared by the optical floating zone method, and characterized by a combination of X-ray diffraction (XRD), and Raman, electron paramagnetic resonance (EPR), ultraviolet–visible (UV–Vis), photoluminescence excitation (PLE) and photoluminescence (PL) spectroscopic techniques. XRD and Raman spectroscopy showed that the crystal samples were all in the cubic phase, whereas the ceramic sample consisted of a mixture of monoclinic and cubic phases. The absorption spectrum showed four peaks at 245, 273, 308, and 314 nm in the ultraviolet region, and the optical band gap differed between samples with ≤3.00 mol% and those with >3.00 mol% Gd₂O₃. The emission spectrum showed a weak peak at 308 nm and a strong peak at 314 nm, which are attributed to the ⁶P_5/2 → ⁸S_7/2 and ⁶P_7/2 → ⁸S_7/2 transitions of Gd³⁺, respectively. The intensities of the peaks in the excitation and emission spectra increased with Gd³⁺ concentration, reached a maximum at 2.00 mol%, then decreased with higher concentrations. This quenching is considered to be the result of the electric dipole-dipole interactions, and this interpretation is supported by the Gd³⁺ EPR spectra, which showed progressive broadening with increasing Gd³⁺ concentration throughout the concentration range investigated.     

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.     

Achieving highly efficient far-red emission from luminescence-ignorable Ca2MgTeO6:Mn4+ to Ca2-zLnzMgTe1-yWyO6:Mn4+ (Ln = La,Y, Gd) phosphors via solid solution and impurity doping strategies

The Mn⁴⁺-doped Ca2MgTeO6 (CMTO) far-red emitting phosphors with double perovskite-type structure were successfully synthesized. Upon near-ultraviolet (n-UV, 300 nm) light excitation, the as-prepared phosphors showed far-red light at 700 nm attributed to the ²E_g→⁴A_2g transition of Mn⁴⁺ ion. The doping concentration of the CMTO:xMn⁴⁺ samples was optimized to be 0.8 mol%. The relevant mechanism of concentration quenching was demonstrated as the dipole-dipole interaction. Furthermore, solid solution and impurity doping strategies were adopted to improve the far-red emission of the luminescence-ignorable CMTO:Mn⁴⁺ phosphor. Series of Ca₂MgTe_(1−y)W_yO₆:0.8 mol%Mn⁴⁺ (y = 0–100 mol%) solid solution and Ca_2−zLn_zMgTe_0.6W_0.4O₆:Mn⁴⁺ (Ln = La, Y, and Gd, z = 10 mol%) phosphors were synthesized through the above two strategies. The luminescence intensity of the optimal Ca_1.9Gd_0.1MgTe_0.6W_0.4O₆:Mn⁴⁺ phosphor was 13.7 times that of the CMTO:Mn⁴⁺ phosphor and 2.51 times that of red commercial phosphor K₂SiF₆:Mn⁴⁺. Notably, both CMTO:Mn⁴⁺ and Ca_1.9Gd_0.1MgTe_0.6W_0.4O₆:Mn⁴⁺ phosphors exhibited remarkable thermal stability compared with most Mn⁴⁺-doped phosphors. Finally, the highly efficient Ca_1.9Gd_0.1MgTe_0.6W_0.4O₆:Mn⁴⁺ phosphor was successfully applied in fabricating the warm white light diode (w-LED). This working along both lines strategy exhibited great potential for luminescence optimization of Mn⁴⁺-doped oxide phosphors.     

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.     

Doping and luminescence mechanisms of broadband NIR-II emitting Zn2(1−x)Ni2xGa3Ge0.75O8 nanoparticles

In this study, Zn_2(1−x)Ni_2xGa₃Ge_0.75O₈ (x = 0.0002, 0.001, 0.002, 0.010, 0.020, and 0.030) nanoparticles with broadband NIR-II emissions were synthesized by a hydrothermal synthesis combined with a vacuum annealing. For the Ni²⁺-doped ZGGO samples (x = 0–0.03), with increasing concentration, the particle shape gradually becomes spherical and the average particle size decreases from 124.4 to 74.2 nm. Meanwhile, for the ZGGO:Ni²⁺_0.01 nanoparticles, the asymmetrically broad emission peak around 1290 nm, which is the superposition of the two peaks locating at 1280 and 1450 nm, can be observed and the afterglow time exceeds 30 min. Based on the spectral data, luminescence decay curves, first-principles calculations, and Tanabe–Sugano theory, it is found that Ni²⁺ ions can occupy not only tetrahedral but also octahedral Zn²⁺ sites (locating in anti-site defects pair) in the spinel ZGGO host, and they have the contributions to the 1450 and 1280 nm emission peaks, respectively. Furthermore, the surface-modified ZGGO:Ni²⁺ nanoparticles exhibited good stability in the H₂O and HSA (5% human serum albumin, pH = 7.4) solutions and the occurred agglomeration sinking in the SLS (simulate lysosomal solution, pH = 4.7) solution. Compared to the narrow-band NIR-II emitting persistent luminescence nanoparticles (ZGGO:Cr³⁺,Er³⁺ and ZGGO:Cr³⁺,Nd³⁺), broadband NIR-II emitting persistent luminescence nanoparticles (ZGGO:Ni²⁺ NIR-II) possess stronger persistent luminescence intensity and can effectively avoid the water absorption of biological tissues. Our results suggest that ZGGO:Ni²⁺ persistent luminescence nanoparticles have a potential to become optical probes for deep-tissue autofluorescence-free bioimaging in the biomedical field.     

Structure,Judd-Ofelt analysis and spectra studies of Sm3+-doped MO-ZnO-B2O3–P2O5 (M = Mg,Ca, Sr,Ba) glasses for reddish-orange light application

In the present work, a series of Sm³⁺-doped MO-ZnO-B₂O₃–P₂O₅ (M = Mg, Ca, Sr, Ba) glasses were prepared. The glass structure and luminescence properties were investigated by XRD, DSC, IR, absorption spectroscopy, Judd-Ofelt theory and photoluminescence spectra. The J-O parameters of Sm³⁺-doped glasses follow the trend of Ω₄＞Ω₆＞Ω₂. Under the excitation of 401 nm Xenon lamp, Sm³⁺-doped glasses exhibited four emissions from the transitions of ⁴G_5/2→⁶H_J/2 (J = 5, 7, 9, 11) in the visible spectra. The luminous intensity of Sm³⁺ increases with the asymmetry in local environments and decreases with the increasing radius of the alkaline-earth cation. Among the as-prepared glass, the Sm³⁺-doped glass containing magnesium oxide exhibits higher values of stimulated emission cross-section (2.18 × 10⁻²¹ cm²), gain bandwidth (1.40 × 10⁻²⁷ cm³), and optical gain (3.83 × 10⁻²⁴ cm²). All the Sm³⁺-doped glasses show intense orange light in the CIE 1931 chromaticity diagram with a high color purity exceeding 99%. In addition, the time-resolved emission spectra reveal the decay process of the Sm³⁺ ions for the transitions ⁴G_5/2 → ⁶H_7/2 and ⁴G_5/2 → ⁶H_9/2 in the glass containing magnesium oxide. It suggests that Sm³⁺-doped alkaline-earth zinc borophosphate glasses could be a potential candidate for reddish-orange light-conversion fluorescent materials based on the ultraviolet light-emitting diode.     

Influence of Al3+ on the cross relaxation process and electrical properties of Dy3+ activated Gd2O3 phosphor for white LED application

Gd₂O₃:Dy³⁺ Al³⁺ phosphors is synthesised by a wet-chemical method for various concentrations of Al³⁺ ion. X-ray diffraction, photoluminescence and impedance spectroscopy are used to understand the physio-chemical properties of the phosphors. The emission spectra of Dy³⁺ ion exhibit transition peaks centred at 572 nm (yellow), 486 nm (blue) and 669 nm (red). Energy transfer from Gd³⁺ to Dy³⁺ is also verified by exciting the phosphors at 274 nm. Some of the Dy³⁺ ions occupy both C₂ and S₆ site of Gd³⁺ ion in Gd₂O₃ matrix. It is also revealed that the enhancement of Dy³⁺ emission is strongly correlated to the surface morphology of the phosphors. Introducing Al³⁺ ions in Gd₂O₃:Dy³⁺ phosphor affect the emission properties of Dy³⁺ ions and its influence is explored at various concentration of Al³⁺ ions. The energy level diagram is presented to explain the cross-relaxation process among Dy³⁺ ions and the energy transfer from Gd³⁺ to Dy³⁺ ion.     

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⁺.     

Enhanced photoluminescence quantum yield of Ce3+-doped aluminum–silicate glasses for scintillation application

Ce³⁺-doped 20Gd₂O₃–20Al₂O₃–60SiO₂ (GAS:xCe³⁺) glasses (x = 0.3, 0.7, 1.1, 1.5, 1.9 mol%) with Si₃N₄ as a reducing agent were prepared. The density of the glasses is around 4.2 g/cm³. With the increase in the Ce³⁺ concentration, both the photoluminescence (PL) and PL excitation peaks of GAS:xCe³⁺ glasses show a redshift because the 4f–5d energy levels of Ce³⁺ ions are narrowed. PL quantum yield and PL decay time of GAS:xCe³⁺ glasses are 28.32–50.59% and 43–64 ns, respectively. In addition, they both first increases and then decreases with the Ce³⁺ concentration increasing, reached the maximum when x = 1.1 mol%. The integrated X-ray excited luminescence (XEL) intensity of the GAS:1.1Ce³⁺ glass is 23.86% of that of Bi₄Ge₃O₁₂ (BGO) crystal, and the light yield reaches 1200 ph/MeV with an energy resolution of 22.98% at 662 keV when exposed to γ-rays. The PL and XEL thermal activation energies of GAS:xCe³⁺ glasses are independent of Ce³⁺ ions concentration. Scintillating decay time of the glasses exhibits two components consisting of nanosecond and microsecond levels, and the scintillating decay time gradually decreases with the Ce³⁺ concentration increasing. The difference between PL and scintillating decay time is discussed regarding the different luminescent mechanisms.     

Optical temperature sensor based on upconversion luminescence of Er3+ doped GdTaO4 phosphors

For the development of optical temperature sensor, a series of GdTaO₄ phosphors with various Er³⁺-doping concentrations (0, 1, 5, 10, 25, 35, 50 mol%) were synthesized by a solid-state reaction method. The monoclinic crystalline structure of the prepared samples was determined by X-ray diffraction (XRD). Under excitations of 980 and 1550 nm lasers, the multi-photon-excited green and red upconversion (UC) luminescence emissions of Er³⁺ were studied, and the critical quenching concentration of Er³⁺-doped GdTaO₄ phosphor was derived to be 25 mol%. By changing the pump power of laser, it was found that the two-photon and three-photon population processes happened for the UC emissions of Er³⁺-doped GdTaO₄ phosphors excited by 980 and 1550 nm lasers, respectively. Furthermore, based on the change of thermo-responsive green UC luminescence intensity corresponding to the ²H_11/2 → ⁴I_15/2 and ⁴S_3/2 → ⁴I_15/2 transitions of Er³⁺ with temperature, the optical temperature sensing properties of Er³⁺-doped GdTaO₄ phosphor were investigated under excitations of 980 and 1550 nm lasers by using the fluorescence intensity ratio (FIR) technique. It was obtained that the maximum absolute sensitivity (S_A) and relative sensitivity (S_R) of Er³⁺-doped GdTaO₄ phosphors are as high as 0.0041 K⁻¹ at 475 K and 0.0112 K⁻¹ at 293 K, respectively. These significant results suggest that the Er³⁺-doped GdTaO₄ phosphors are a promising candidate for optical temperature sensor.     

Novel coated graphite electrode for the selective determination of Gd(III) in rocks and waste water samples

A novel gadolinium selective coated graphite electrode based on 2,6-bis-[1-{N-cyanopropyl,N-(2-methylpridyl)}aminoethyl]pyridine [P] is described. The best performance was exhibited by the electrode having membrane composition P:NaTPB:PVC:NPOE as 8:4:30:58 (%, w/w). The electrode demonstrates excellent potentiometric characteristics towards gadolinium ion over several interfering ions. The electrode exhibited a Nernstian response to Gd³⁺ ion over a wide concentration range 2.8 × 10⁻⁷ to 5.0 × 10⁻² M with a detection limit (6.3 ± 0.1) × 10⁻⁸ M and slope 19.6 ± 0.1 mV decade⁻¹ of a_Gd³⁺. Furthermore, it showed a fast response time (12 s) and can be used for 2.5 months without significant divergence in its characteristics. Noticeably, the electrode can tolerate the concentration of different surfactants up to 1.0 × 10⁻⁴ M and can be used successfully in 30% (v/v) ethanol media and 10% (v/v) methanol and acetonitrile water mixture. The useful pH range of this sensor is 2.0 to 8.0. It is sufficiently selective and can be used for the determination of Gd³⁺ ions in waste water and rock samples. It also serves as a good indicator in the potentiometric titration of GdCl₃ with EDTA.