Characteristic Emission Of Eu3 Research Articles

Designing Tb3+‐Sensitized Silica‐Nanoparticles‐Aided Eu3+‐Doped Sr2SiO4 Phosphors with Enhanced Luminescence for Anti‐Counterfeiting Applications

Silica‐nanoparticles‐assisted Eu3+‐doped Sr2SiO4 and Tb3+‐ and Eu3+‐co‐doped Sr2SiO4 phosphors, as potential phosphors for anti‐counterfeiting application are synthesized via a solid‐state reaction technique. The crystal structure, photoluminescence, and decay times are investigated. The characteristic emission of Eu3+‐doped Sr2SiO4 phosphors exhibits two major peaks at 617 and 595 nm under an excitation wavelength of 394 nm, which corresponds to 5D0 → 7F2 and 5D0 → 7F1 electron transitions of Eu3+ ions. Upon co‐doping with Tb3+, the red emission intensities of the Eu3+‐doped Sr2SiO4 phosphors are enhanced by 1.78‐fold times through an energy‐transfer process. The optimized Tb3+‐ and Eu3+‐co‐doped Sr2SiO4 phosphors show a decay time of 0.49 ns and an energy‐transfer efficiency of 73%. The calculated International Commission on Illumination value (x, y) and color purity are (0.63, 0.37) and 94%, respectively. Subsequently, a luminescent ink is formulated using the optimized phosphor and tested for efficiency on currency notes. Additionally, a flexible film is fabricated, and its luminescence properties are studied. The formulated ink can serve as security ink in the anti‐counterfeiting application.

Plasma‐Generated Luminescent Coatings: Innovations in Thermal Sensitivity and Corrosion Resistance

AbstractThe strategic design of traditional coating materials has long been pivotal in broadening their range of applications. In this work, europium‐doped TiO2 coatings are grown in situ on the surface of titanium substrate using plasma electrolytic oxidation technology. The core reaction took no more than five minutes. Incorporating europium into the coating preserved the inherent corrosion resistance of PEO coatings while imparting anticipated thermal‐sensitive luminescence capabilities. The intrinsic emission of TiO2 and the characteristic emission of Eu3+ (5D0 → 7F2) are employed as the self‐reference for the LIR thermometry. The absolute and relative temperature sensitivity of the coating reached 0.0087 K−1 and 0.739% K−1, respectively. Notably, the coating exhibited a signal discriminability of up to 5100 cm−1 and a temperature uncertainty of only 0.18 K, which is comparable to some TiO2: Eu nanoparticles. The ingenious fusion of corrosion resistance and thermal‐sensitive luminescence of the coating not only makes it a classic protective structure but also facilitates its applicability to diverse scenarios, including optical thermometry in extreme environments.

Efficient Multi-stimulus-Responsive Luminescent Eu(III)-Modified HOFs Materials: Detecting Thiram and Caffeic Acid and Constructing a Flexible Substrate Anti-counterfeiting Platform.

The powerful capability of multi-stimulus-responsive luminescent hydrogen-bonded organic frameworks (HOFs) to respond to external chemical or physical stimuli in various manners makes them appealing in the luminescence anti-counterfeiting field. Herein, a novel Eu3+-functionalized HOF (Eu@GC-2) that combines the emission of HOFs with the characteristic emission of Eu3+ ions has been successfully synthesized, which can generate various fluorescence at different excitation wavelengths. Eu@GC-2 has enormous potential as a raw material for a paper-based sensor that is designed for detecting the pesticides thiram and caffeic acid in crops with favorable selectivity, anti-interference, and high efficiency. Based on the above excellent properties, Ln3+-functionalized HOFs (Ln@GC-2) were then employed to produce four luminescent anti-counterfeiting inks. With the incorporation of back-propagation neural network and Gray code conversion functions, a multi-stimulus-responsive luminescent anti-counterfeiting platform, coregulated by the excitation light and the chemical reagent, has been constructed. This approach can not only achieve multiple encryptions and fast information identification but also enhance the code-breaking complexity, making it an efficient strategy for information encryption and decryption.

Cd-MOF and Its Ln3+-Post Modification Products: Regulation of Luminescence Properties and Improved Detection of Uric Acid, Quinine, and Quinidine.

One 3D Cd-MOF, namely, {[(HDMA)2][Cd3(L)2]·5H2O·2DMF}n (LCU-124, LCU indicates Liaocheng University), was synthesized from an ether-containing ligand 1,3-bis(3,5-dicarboxylphenoxy)benzene (H4L). Its Ln3+-postmodified samples, Eu3+@LCU-124 and Tb3+@LCU-124, were obtained through cation exchange of dimethylamine cation (HDMA) with Eu3+ and Tb3+. The successful entry of rare earth into LCU-124 by cation exchange modification was verified by IR, XRD, XPS, EDS mapping, and luminescence spectra. The proportion of Eu3+/Tb3+ was adjusted during the modification process, leading to fluorescent materials with different emissions. Luminescence measurements indicated that these complexes exhibited interesting multiresponsive sensing activities toward biomarkers urine acid (UA), quinine (QN), and quinidine (QND). First, LCU-124 has a pronounced quenching effect toward UA with the detection limit of 31.01 μM. After modification, the visualization of the detection was improved significantly and the detection limit of Eu3+@LCU-124 was reduced to 0.868 μM. Second, when QN and QND were present in the suspensions of Eu3+@LCU-124 and Tb3+@LCU-124, strong blue light emission peaks occurred, while the characteristic emission of Eu3+/Tb3+ decreased, forming ratiometric fluorescent sensors with the detection limit in the range of 0.199-9.49 μM. The fluorescent probes have high selectivity, excellent sensitivity recycling, and fast response time (less than 1 min). Besides, a simple logic gate circuit and a range of luminescent mixed matrix membranes were designed to provide simple and fast detection of above biomarkers. Our work indicated that modification of Eu3+/Tb3+ could improve the detection ability significantly.

Studies on a novel SrZr2 CaLa2 O8 :Eu3+ phosphor for lighting applications emitting direct white light.

Direct white light emitting phosphors play a significant role in the display industry due to their ability to improve the quality, efficiency, and versatility of lighting sources used in most of the displays. The currently investigated phosphor SrZr2 CaLa2 O8 :Eu3+ was prepared by a conventional solid-state reaction method. It has been observed that the stoichiometric ratio of all precursors plays an important role in determining the characteristics of the final phosphor. From X-ray diffraction (XRD) analysis, the phosphor was observed to have a hexagonal phase and a crystal size of ~28 nm. Scanning electron microscopy (SEM) observations revealed a cluster of rod-like structures with an average diameter of ~0.2μm. The excitation peak maximum observed at 280 nm is due to charge transfer between Eu3+ -O2- ions. The energy transitions 7 F0 → 5 L6 and 7 F0 → 5 D2 are responsible for the appearance of other excitation peaks at ultraviolet (UV) (395 nm), blue (~467 nm), green (~540 nm), orange (~590 nm), and red (~627 nm) attributed to 5 D0 → 7 FJ (J = 0-4) transitions of europium ion (Eu3+ ). The Commercial International de I'Eclairage (CIE) chromaticity coordinates were estimated to be (0.37, 0.0.33) and (0.67, 0.33) for the emissions corresponding to 395 and 590 nm, respectively. The characteristic emissions of Eu3+ ions allow this novel phosphor to be used to generate direct white light in light-emitting diodes (LEDs), which is otherwise difficult to achieve in single-component systems.

Ratiometric fluorescent sensor based on metal–organic framework for selective and sensitive detection of CO32–

Carbonate ion (CO32–) is an anion essential for the maintenance of life activities and is of great importance to human health. Here, a novel ratiometric fluorescent probe Eu/CDs@UiO-66-(COOH)2 (ECU) was prepared by introducing europium ions (Eu3+) and carbon dots (CDs) into the UiO-66-(COOH)2 parent framework under the guidance of a post-synthetic modification strategy and used for the detection of CO32– ion in the aqueous environment. Interestingly, when CO32– ions were added to the ECU suspension, the characteristic emission of carbon dots at 439 nm was significantly enhanced, while the characteristic emission of Eu3+ ions at 613 nm was reduced. Therefore, the detection of CO32– ions can be realized through the peak height ratio of the two emissions. The probe had a low detection limit (about 1.08 μM) and a wide linear range (0–350 μM) for the detection of carbonate. In addition, the presence of CO32– ions can cause a significant ratiometric luminescence response and resulted obvious red-to-blue color shift of the ECU under UV light, which will facilitate visual analysis by the naked eye.

Blue-Emitting Ligand-Mediated Assembly of Rare-Earth MOFs toward White-Light Emission, Sensing, Magnetic, and Catalytic Studies.

New lanthanide carboxylate compounds with two- (2D) and three-dimensional (3D) structures have been prepared by employing 2,5-bis(prop-2-yn-1-yloxy)terephthalic acid (2,5-BPTA) as an organic linker. The compounds, [Ln(C14H8O6)(C7O3H4)·2H2O]·4(H2O), Ln = Y, Pr, Nd, Sm, Eu, Gd, Tb, Dy and [Ln(C7O3H4)3·(C3H7ON)·(H2O)]·2(H2O)(C3H7NO), Ln = La, Ce, Pr, have two- and three-dimensional structures, respectively. In all compounds, lanthanide ions are connected together, forming a dimer, which is connected by the 2,5-BPTA ligand. In the two-dimensional structure, there are two 2,5-BPTA moieties present, and in the three-dimensional structure, there are three 2,5-BPTA moieties present. The lanthanide centers are nine-coordinated, the 2D structure has a tricapped trigonal prismatic arrangement, and the 3D structure has a monocapped distorted square antiprismatic arrangement. The Pr compound forms in both 2D and 3D structures, whose formation depends on the time of the reaction (2 days─2D and 5-6 days─3D). The ligand emits in the blue region, and using the characteristic emission of Eu3+ (red) and Tb3+ (green) ions, we achieve white light emission in the (Y0.96Tb0.02Eu0.02) compound. The overall quantum yield for the white light emission is 28%. The strong green luminescence of the Tb3+-containing compound was employed to selectively sense the Cr3+ and Fe3+ ions in aqueous solution with limits of detection (LODs) at 0.41 and 8.6 ppm, respectively. The Tb compound was found to be a good heterogeneous catalyst for the Ullman-type O-arylation reaction between phenol and bromoarene with yields of 95%. Magnetic studies on the Gd-, Tb-, and Dy-containing compounds showed weak exchange interactions within the dimeric Ln2 units. The present work demonstrates the many utilities of the rare-earth-containing MOFs, especially toward white-light emission, metal-ion sensing, and heterogeneous catalysis.

Photoluminescence and electrochemical performance evaluation of Eu3+ doped MgAl2O4 phosphors for LED and energy storage applications

Crystal structure of Eu3+ doped MgAl2O4 (MAO) phosphors synthesised by solid state reaction method was investigated using X-ray diffraction. Raman peaks appeared at 307 cm−1, 408 cm−1, 668 cm−1 and 767 cm−1 were assigned to F2g (1), F2g (2), Eg and A1g respectively. Spherical morphology and microstructural analysis of synthesised phosphors was analysed by Field emission scanning electron microscope (FESEM) high resolution transmission electron microscope (HRTEM) and energy dispersive X-ray analysis (EDAX) was used to establish the chemical composition of the phosphors. Optical properties were analysed by photoexcitation (394 nm) and photoluminescence (PL) spectra displayed all the characteristic emission of Eu3+ related to transition 5D0 to 7Fj (j = 0, 1, 2, 3, 4). The emission color was observed in red region and it was confirmed by the Commission Internationale de l’Eclairage (CIE) chromatic coordinate graph. The color purity and quality (correlated color temperature- CCT value) of red light was observed in 0.9% Eu3+ doped MAO to be 90.76% and 2097K respectively. Electrochemical evaluation of Eu3+ doped MAO was performed through cyclic voltammetry (CV) studies.

Blue-light excitable red-emitting Eu3+-doped TiO2 phosphor for WLED applications: Judd-Ofelt analysis and systematic investigation on its optical properties

Red-emitting Eu3+-activated TiO2 phosphors with excellent color purity of 99.9% have been successfully synthesized by a facile sol-gel method. PLE spectrum demonstrates that the obtained products have absorption bands ranging from 370 to 540 nm, with the highest band peaking at 464 nm. Under the blue excitation of 464 nm, the characteristic emissions of Eu3+ ions corresponding to the 5D0 → 7FJ transitions are observed, with the dominant emission peak at 614 nm. The optimal annealing temperature and dopant concentration are 5 h at 500 °C and 1.3 mol%, respectively. The PL quenching mechanism is attributed to the dipole-quadrupole interaction. The Judd-Ofelt analysis is carried out to explore the local structure environment around the Eu3+ ions. It is found that the highest asymmetry of the local environment surrounding Eu3+ ions and the strongest covalence Eu-O bond is attained at the annealing temperature of 500 °C and the activation energy is determined to be 0.385 eV. The fluorescence lifetime of the 614 nm emission was found to be 0.44 ms. These results indicate that the Eu3+-doped TiO2 phosphor may be a promising red-emitting phosphor for white light-emitting diodes.

A novel ratiometric fluorescence sensor based on lanthanide-functionalized MOF for Hg2+ detection

Post-synthesis modification is an effective strategy for the preparation of rare earth organic framework materials and the derivation of high-performance functional materials. Here, we report the preparation of a dual emission Ln-MOF material (Eu-Ca-MOF) using Ca-MOF as the parent framework and introducing Eu3+ ions into its channels through post-synthesis modification. Eu-Ca-MOF has good photoluminescence properties and can be used as a ratiometric fluorescence sensor (I381/I590) to detect Hg2+ ions in water sensitively. The characteristic of Eu-Ca-MOF obtained is that when the material is dispersed in an aqueous solution containing Hg2+ ions, the characteristic emission of the ligand at 381 nm is enhanced, while the characteristic emission of Eu3+ at 590 nm is quenched. The peak-to-height ratio of the two emissions can be used to achieve highly sensitive detection of Hg2+ ions even in the presence of other potentially competing analytes. In addition, Hg2+ induces Eu-Ca-MOF to produce a significant ratiometric luminescence response, which changes its luminescence color from red to blue, which is beneficial to visual analysis of naked eyes. At the same time, Eu-Ca-MOF has a wider detection range (0.02–200 μM), and a lower limit detection (2.6 nM) for Hg2+ ions. The lanthanide compounds prepared by post-synthetic modification provide an effective synthesis strategy for photoluminescent materials.

Three-step post-synthetic modification metal-organic framework as a ratiometric fluorescent probe for the detection of creatinine

Creatinine (Cre) measurement in biological fluids is an increasingly important clinical measure for evaluating renal insufficiency, thyroid dysfunction, and muscle injury. Therefore, a simple, fast, and reliable Cre analysis method is of great significance to human health. Herein, a novel ratiometric fluorescence sensor, Ag-Eu-MOF-808-EDTA, was synthesized by introducing ethylenediaminetetraacetic acid (EDTA), Ag+, and Eu3+ into the framework of MOF-808 through three steps of post-synthesis modification, and was used to detect Cre in PBS buffer of pH 7.2 at 35 °C with a “turn-on” ratio response in the presence of various interfering ions and several biomolecules. In this strategy, the characteristic emission of Eu3+ at 551 nm can be turned on due to coordination between Cre and Ag+, while emission at 613 nm is independent of Cre, which produces a significant ratio response change throughout the cycle. Experimental results showed that the ratio fluorescence sensor displayed a wide linear range for Cre from 0.5 to 350 μM with a low detection limit of 0.42 μM. Finally, a good recovery rate (96.7–102.9%) and appropriate relative standard deviation (RSD <2.39%, n = 3) were obtained during the determination of creatinine in real urine and serum. This work provides additional insights into the detection of creatinine in clinical blood samples.

Two multifunctional LnMOFs as recyclable luminescent sensors for sensitive detection of nitro-aromatic compounds

Two isostructural lanthanide metal-organic frameworks (LnMOFs), MOF1 and MOF2, were synthesized by solvothermal reaction. The composition and morphology of MOF1 and MOF2 were characterized by FT-IR, EDX, TG, PXRD, et al. The fluorescence spectra show that MOF1 and MOF2 have the significant characteristic emission bands of Eu3+ and Tb3+ ions, respectively. Based on the characteristic emissions of Eu3+ and Tb3+ in MOF1 and MOF2, we studied the fluorescence sensing experiments of them to aromatic compounds. The results show that MOF1 and MOF2 both exhibit significant fluorescence quenching effect toward p-nitroaniline, o-nitrophenol and p-nitrophenol with good selectivity and sensitivity. Furthermore, the anti-interference and recyclability were carried out. All the results confirm MOF1 and MOF2 can be used as potential sensing materials for the selective detection of environment pollutants.

Photoluminescence and electrochemical performances of Eu3+doped La10Si6O27 nanophosphor: Display and electrochemical sensor applications

The current work involves the synthesis of a series of Eu3+ (1–11 mol%) doped La10Si6O27 nanophosphors (ELNPs) by solution combustion method using oxalyl dihydrozil (ODH) as a fuel for the first time. The PXRD studies revealed the average crystallite size in the range 15–35 nm for ELNPs. DRS studies revealed the energy gap of Eu3+ (1–11 mol %) doped La10Si6O27 is ~5.4 eV. The Photoluminescence (PL) studies of the ELNPs showed all the characteristic emission of Eu3+ cations and optimal emission intensity was observed for 5 mol % concentration of Eu3+ ions. The excitation maxima detected at 360 nm, 379 nm, 391 nm, 400 nm, 413 nm and 462 nm were conformed to transitions from 7F0→5G3, 5G4, 5L6, 5D4, 5D3 and 5D2 states of Eu3+ ions respectively. The observed intensities of PL transitions clearly indicated great potentiality for the fabrication of blue/near UV-LED excited phosphor for WLEDs. The calculated CIE chromaticity coordinates confirm the red emission and were depicted in the CIE diagram. The paracetamol and penegra materials were effectively sensed by the prepared carbon paste electrode of Eu3+ (3 mol %) doped La10Si6O27 as revealed by cyclic voltammetric and EIS studies. All the above results show that the synthesized ELNPs can be a potential candidate for display and electrochemical sensor applications.

Study of Radiophotoluminescence of Eu Doped CaSO4 Phosphor for Gamma Dosimetric Applications

CaSO4:Eu phosphor is synthesised by acid distillation method with varying synthesis parameters for studying its Radiophotoluminescence (RPL) properties for gamma absorbed dose measurements. Five phosphor samples are prepared by varying quantity of solvent, distillation temperature and reaction time. XRD, SEM, particle size analysis and photoluminescence studies are carried out. The characterisation study shows polycrystalline luminescent particles of average size varying from 35 μm to 55 μm. Characteristic emission of Eu3+ is observed around 590, 615 and 620 nm at 242 nm excitation. Gamma dose response of maximum Eu3+ PL intensity sample is studied in the range 10 cGy to 1000 cGy using Co-60 source. Gamma radiation exposure induces conversion of Eu3+ to Eu2+ giving luminescence at 385 nm with 320 nm excitation. Repetitive measurements of gamma exposed samples are carried out and no significant fading is observed within one week of post-irradiation. The phosphor has the potential to be used for gamma dosimetry.

Color tunable luminescence and optical temperature sensing performance in a single-phased KBaGd(WO4)3:Dy3+, Eu3+ phosphor

Abstract Herein, a series of Dy3+, Eu3+ single/co-doped KBaGd(WO4)3 phosphors (KBGW:Dy3+, Eu3+ for short) were prepared by solid-state reaction method and investigated by means of X-ray diffraction, SEM, photoluminescence excitation and emission spectra, decay curves and thermal quenching behavior. The KBGW:xDy3+ phosphors exhibited a weak blue emission around 480 nm and a strong yellow emission around 580 nm, corresponding to the characteristic 4F9/2 → 6H15/2 and 4F9/2 → 6H13/2 transitions of Dy3+ ions respectively. The decay curves of the KBGW:xDy3+ phosphors were analyzed in the framework of the Inokuti-Hirayama (IH) model and the concentration quenching mechanisms were determined to be dipole-dipole interactions. Under the excitation of 250 nm and 352 nm, both the characteristic emissions of Eu3+ and Dy3+ ions were observed in the KBGW:Dy3+, Eu3+ phosphors. Furthermore, with the increasing concentration of Eu3+, color-tunable emissions from yellow to red were obtained in these samples. Based on the thermal quenching behavior, the optical sensitivity of the sample to temperatures, including absolute sensitivity (Sa) and relative sensitivity (Sr), were calculated and evaluated for the application in optical thermometry.

Synthesis and luminescence properties of novel host-sensitized germanate phosphors NaYGeO4:Ln (Ln = Eu3+, Sm3+, Dy3+)

The rare earth ions doped germanate phosphors NaYGeO4:Ln (Ln = Eu3+, Sm3+ and Dy3+) as well as pure NaYGeO4 host were synthesized by conventional high-temperature solid-state reaction method. The results of X-ray diffraction along with Rietveld refinement revealed the formation of the single orthorhombic phase of the as-prepared phosphors. The pure host NaYGeO4 showed broad excitation/emission band in UV–vis region, which could result from the transition of self-activated optical centers in the GeO4 anion. The host sensitization for Eu3+/Sm3+/Dy3+ emission in NaYGeO4 was confirmed and the energy transfer efficiency from the host to Eu3+/Sm3+/Dy3+ was calculated. Upon excitation with ultraviolet light (300 nm), the as-synthesized NaYGeO4:Ln (Ln = Eu3+, Sm3+ and Dy3+) phosphors showed both the blue broadband emission of the NaYGeO4 host and the characteristic emission of Eu3+/Sm3+/Dy3+ ions, which led to apparent change of the CIE chromaticity coordinates compared to the pure NaYGeO4 host. These results implied the potential application of the as-prepared phosphors in UV light-emitting diodes.

Structures and luminescence properties of y at.% Eu3+-doped Y(Ta1−xPx)O4 phosphors

UV-activated phosphors Y(Ta1−xPx)O4:y at.% Eu3+ for solid state lighting were synthesized by high temperature solid-state method. The crystal structures and luminescent characteristics of Y(Ta1−xPx)O4:Eu3+ phosphors were investigated in detail. It is found that PO43− can enter into YTaO4 crystal structure with a maximum doping concentration of 1%. And the luminescence performances of Y(Ta1−xPx)O4:Eu3+ can be continuously improved with the increase of PO43− doping. Gauss fitting analysis demonstrates that the excitation bands of Y(Ta1−xPx)O4:Eu3+ are mainly composed of charge transfer bands of TaO43− (peak center is located in 230 nm) and Eu3+ (peak center is located in 250 nm) which indicates that TaO43− has energy transfer effect on Eu3+ 615 nm emission. The characteristic emissions of Eu3+ excited by 250 nm ultraviolet light occurred at 595 nm (assigned to 5D0→7F1) and 615 nm (assigned to 5D0→7F2), respectively. It is of particular note that the color coordinates of Y(Ta0.99P0.01)O4:Eu3+ in the yellow-red region can be modulated by changing the doping concentrations of Eu3+. And the optimum doping concentration of Eu3+ with the strongest luminous intensity and the highest color purity is 7 at.%.

Photoluminescence and cathodoluminescence of spin coated ZnO films with different concentration of Eu3+ ions

ZnO thin films doped with Eu3+ up to 4 mol% were successfully prepared using a sol-gel spin coating technique. The structure, morphology, chemical analysis and luminescence of the films were studied. X-ray photoelectron spectroscopy (XPS) analysis for the Eu 3d core shells confirmed the presence of divalent (Eu2+) and trivalent (Eu3+) states. Time of flight secondary ion mass spectroscopy showed that the Eu3+ions were homogeneously distributed throughout the thin film with Eu2+ mainly only in the surface region of the thin films. The films exhibited ZnO exciton emission around 376 nm, broad defect related emission and the Eu3+ characteristic emission simultaneously when excited at 325 nm. For the excitation at 464 nm, the doped samples exhibited only the characteristic emissions of Eu3+ which were attributed to the 5D0-7FJ (J = 0, 1, 2, 3, 4) transitions, respectively. The film with a 3 mol% of Eu3+ has emitted the highest photo/cathodoluminescence (PL/CL) emission. Therefore, it was subjected to electron beam irradiation in vacuum for about 22 h to establish the effect of the electron beam on the film's surface state, chemical and luminescence stability. Minor surface modification during electron beam irradiation was observed. The O 1s XPS peak revealed the creation of new defects associated with oxygen deficiencies due to the irradiation. Surface modification and creation of defects were identified as the major mechanisms for the initial decrease in the CL intensity. This film was very stable during prolonged electron beam irradiation.

Novel synthesis of silica-coated Eu:Gd2O3 nanoparticles by polyol route at low temperature for bimodal cancer imaging

This article reports the novel synthesis of europium doped gadolinium oxide (Eu:Gd2O3) nanoparticles at low temperature by the polyol method for the first time. The role of triethylene glycol (TEG) on the magnetic and optical properties was studied. The cytotoxicity of the nanoparticles and their applications in magnetic resonance imaging (MRI) and optical imaging was also reported. Silica is coated over the nanoparticles to improve the biocompatibility. Spherical nanoparticles with an average diameter of ∼40 nm were synthesized and silica with thickness around 5 nm was coated on the nanoparticles. In the photoluminescence studies, the characteristic emission of Eu3+ ions at 612 nm due to the 5D0 → 7F2 transition was observed. The lifetime of the uncoated and silica-coated nanoparticles were found to be 1.14 and 0.83 ms respectively. The cell viability was assessed in MG63 osteosarcoma cell line by the MTT assay. The results show that the silica-coated nanoparticles possess negligible toxicity till the concentration of 200 μg ml−1. Within this limit, as the concentration of the nanoparticle is increased, the MRI results reveal bright contrast images with the relaxivity value of 4.8 mM−1 s−1, which is higher than the commercially available contrast agents.

Luminescence properties and energy transfer of a color-tunable Y2GeO5: Bi3+, Eu3+ phosphor

A series of Y2GeO5: Bi3+, Eu3+ phosphors were synthesized via a solid state reaction. Their crystal structures and luminescent properties were investigated. Under the 295 nm excitation of Bi3+, the Y2GeO5: Bi3+, Eu3+ phosphors presented a purplish-blue broad band at 369 nm from Bi3+ and some typical f-f characteristic emissions of Eu3+. The optimum co-dopant concentration of Eu3+ ion is 2%. Luminescence quenching of Eu3+ ions was demonstrated to be quenching interaction of Eu3+-Eu3+ and the quenching of the 5D0 state by Bi3+ ions. Energy transfer from Bi3+ to Eu3+ in Y2GeO5 efficiently occurred and the dipole-dipole interaction is the major energy transfer mechanism. With the increasing concentration of Eu3+, the luminous efficacy of the radiation increases and the luminescence colors can be tuned from purplish blue to reddish-orange. The Y2GeO5: Bi3+, Eu3+ phosphors are potential candidate materials for application in UV chip based W-LEDs with excellent thermal stability (0.2708 eV).