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Highly transparent Ho:Y2O3 ceramics for laser diode lighting were prepared using the vacuum sintering method with 0.3 at.% Nb2O5 as a sintering additive. The microstructures, transmittance, and luminescence properties of the Ho:Y2O3 ceramic samples were investigated in detail. The transmittance levels of all samples with various Ho3+ concentrations reached ~81.5% (2 mm thick) at 1100 nm. Under the excitation of 363 nm (ultraviolet) or 448 nm (blue) light, Ho:Y2O3 transparent ceramic samples showed that green emission peaked at 550 nm. The emission intensity was strongly affected by the concentration of Ho3+ ions, reaching its highest level in the sample doped with 1 at.% Ho3+. The CIE coordinates of the luminescence were in the green region (i.e., the CIE coordinates of the sample doped with 1 at.% Ho3+ were [0.27, 0.53] and [0.30, 0.69], under the excitation of 363 nm and 448 nm light, respectively). The possibility of its application as laser diode lighting was reported. Under the excitation of 450 nm blue laser, the sample doped with 0.5 at.% Ho3+ had the best performance: the saturated luminous flux, lumen efficiency, and the luminescence saturation power densities were 800 lm, 57.7 lm/W, and 17.6 W/mm2, respectively. Furthermore, the materials have high thermal conductivity and mechanical strength due to their host of rare-earth sesquioxide. Thus, Ho:Y2O3 transparent ceramics are expected to be a promising candidate for green-light-emitting devices for solid-state lighting, such as laser diode lighting. [ABSTRACT FROM AUTHOR]

Three europium(III) complexes, Eu(ectfd)3 (Hectfd = 1-(9-ethyl-9H-carbazol-7-yl)-4,4,4-trifluorobutane-1,3-dione), Eu(tta)3 (Htta = 4,4,4-trifluoro-1-(thiophen-2-yl)-butane-1,3-dione), and Eu(dbt)3 (Hdbt = 2-(4',4',4'-trifluoro-1',3'-dioxobutyl)dibenzothiophene), were synthesized and employed to detect total bilirubin (BR) in blood-serum samples. UV-visible absorption and fluorescence (FL) spectroscopies were used to evaluate the selectivity of each europium (III) fluorescence probe to BR, which was shown to remarkably reduce the luminescence intensities of the europium(III) complexes at a wavelength of 612 nm. The luminescence intensity of each complex is linearly related to BR concentration. Eu(tta)3 was shown to be the more-appropriate fluorescence probe for the sensitive and reliable detection of total BR in blood serum samples than either Eu(ectfd)3 or Eu(dbt)3. This observation can be ascribed to special σ-hole bonding between Htta and BR. In addition, the optimal pH test conditions for the detection of BR in human serum by the Eu(tta)3 probe were determined. Sensitivity was shown to be dramatically affected by the pH of the medium. The experimental results reveal that pH 7.5 is optimal for this probe, which coincides with the pH of human serum. Furthermore, BR detection using the Eu(tta)3 luminescence probe is simple, practical, and relatively free of interference from coexisting substances; it has a minimum detection limit (DL) of 68 nM and is a potential candidate for the routine assessment of total BR in serum samples.ᅟ [ABSTRACT FROM AUTHOR]

Eu 3+ -doped Lanthanum gadolinium hafnates (La 0.8 Gd 1.2 Hf 2 O 7 ) transparent ceramics with different Eu 3+ concentration were fabricated by vacuum sintering. XRD results showed all the ceramics are cubic pyrochlore structure. The effects of annealing process on in-line transmittance and luminescence behavior of the Eu 3+ -doped La 0.8 Gd 1.2 Hf 2 O 7 transparent ceramics were investigated. Before annealing, the in-line transmittance of the ceramics was low and the luminescence intensity was weak. As Eu 3+ doping content increased, the transmittance as well as the luminescence intensity decreased. This was ascribed to oxygen vacancy and other defects in the ceramics resulted from the vacuum sintering. After annealing, the transmittance and luminescence intensity were raised, indicating the elimination of oxygen vacancy. Moreover, with the increase of Eu 3+ doping content from 1 at% to 10 at%, the luminescence intensity increased without concentration quenching. [ABSTRACT FROM AUTHOR]

3 at.% Eu3+-doped La2− 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. [ABSTRACT FROM AUTHOR]

Abstract: NaYF4 co-doped with Gd3+ and Mn2+ nanocrystals were synthesized by a solvothermal route with PEI as the surfactant. X-ray diffraction analyses evidenced that the phases of synthesized NaYF4: Gd3+, Mn2+ nanocrystals were all pure cubic structure. The luminescence intensity of 20mol% Gd3+ doped NaYF4 was stronger than that of any other concentration under the 272nm excitation. The photoluminescence emission intensity of NaYF4: Gd3+, Mn2+ at 561nm was increased with the increase of Gd3+ doping concentration. The energy transfer mechanisms between Gd3+ and Mn2+ were discussed. The results showed that the energy level of 6PJ of Gd3+ ions played a key role in the energy transfer process. Furthermore, the Mn2+ ions doped NaYF4: Gd3+ nanocrystals with a strong green emission and proper paramagnetism originated from Gd3+ and Mn2+ may find potential applications in bio-probes and magnetic resonance imaging. [Copyright &y& Elsevier]

• Highly transparent and submicrometer-grained Yb:Y 2 O 3 ceramics were prepared only by hot pressing for the first time. • The mechanical properties of hot-pressed Yb:Y 2 O 3 transparent ceramics have better mechanical properties than pressureless sintered samples. • The highest transmittance of the Yb:Y 2 O 3 ceramic was 81.7% at 1100 nm and 77.2% at 600 nm, which is near the theoretical value. Highly transparent and submicrometer-grained Yb:Y 2 O 3 ceramics were obtained by hot-pressing method with ZrO 2 sintering additive. Hot-pressing method provides extra driving force to promote the densification of Yb:Y 2 O 3 transparent ceramics, resulting in high transmittance achieved. The transmittances of all samples were ranging from 80.5% to 81.8% at 1100 nm and 72.7–77.7% at 600 nm. The ceramic samples in this work were sintered at a low temperature of 1600 ℃ for 3 h, providing dense microstructures with average grain size less than 1 µm, which are smaller than those of Yb:Y 2 O 3 ceramics prepared by other traditional sintering techniques. The microhardness and fracture toughness were ranging from 8.16 to 7.99 GPa, and from 0.94 to 0.88 MPa·m1/2, respectively, which are higher than the comparison samples fabricated by pressureless sintering. The absorption cross-sections of the 1 at% Yb-doped sample at 950 and 976 nm were 0.93 × 10−20 and 1.22 × 10−20 cm2, respectively. The fluorescence decay lifetime at 1032 nm was in the range of 0.79–1.36 ms. According to the available literature, this is the first report about Yb:Y 2 O 3 transparent ceramics fabricated by hot-pressing sintering without any combined sintering process. The ceramics obtained may have potential use for solid-state lasers partly replacing single crystals. [ABSTRACT FROM AUTHOR]

Abstract: Spherical monodispersed, submicron-sized Er3+:Y2O3 powders were prepared via a homogeneous precipitation method using nitrates and urea as raw materials. The structure, phase evolution and morphology of Er3+:Y2O3 precursor and the calcined powders were studied by means of XRD, TG/DTA, FTIR and SEM methods. The upconversion spectra of spherical monodispersed Er3+:Y2O3 powders were excited with 980nm laser diode (LD) and measured by a spectrofluorometer. The results showed that monodispersed spherical powders with a particle size of 200–210nm were obtained after the precipitates were calcined at 800°C for 2h. The solution concentration of Er3+ and Y3+ had a significant impact on the morphologies of the precursor and powders. Low solution concentration such as 0.015M can promote precipitation precursor to keep uniform spherical shape. The resultant monodispersed Er3+:Y2O3 phosphors exhibit upconversion luminescence properties and the intensity of the upconversion luminescence reaches the maximum when the Er3+ concentration is 3at.%. [Copyright &y& Elsevier]

A new composition of phosphor material AlON:Er3+ codoped with Mg2+ were prepared by solid-state reaction method. The effect of Mg2+ dopants on upconversion luminescence properties of the AlON:Er3+ phosphor was investigated. At certain concentrations, Mg2+ dopants were found to greatly enhance the red emission intensity of AlON:Er3+ phosphors. From our results, the enhancement of the emission intensity by Mg2+ dopants was discussed in terms of the Er3+ distribution in crystal lattice and crystal symmetry by introducing oxygen vacancy. [ABSTRACT FROM AUTHOR]

Abstract 1 1 Dissolved oxygen, DO; gaseous oxygen, GO; metal-to-ligand charge transfer, MLCT; 2-thenoyltrifluoroacetonate, TTA; polystyrene, PS. A luminescent film comprising Eu (Ш)-doped yttrium oxide nanosheets was fabricated by electrophoretic deposition, modified by 2-thenoyltrifluoroacetonate, and coated with polystyrene to obtain a novel oxygen sensor capable of detecting both dissolved (DO) and gaseous (GO) oxygen based on luminescence intensity quenching. Based on the results of luminscence lifetime, the mechanism of molecular oxygen–induced luminescence quenching was discussed in detail. The above film exhibited high sensitivity and a well-linear response, with its high photostability making it a promising material for DO and GO sensing. [ABSTRACT FROM AUTHOR]

Submicron-sized Dy 3+ : Y 2 O 3 particles were successfully prepared via an urea homogeneous precipitation method, followed by a calcination at 800 °C. TG-DSC, FT-IR, X-ray diffraction (XRD), Field emission scanning electron microscope (FE-SEM), scanning electron microscope (SEM), photoluminescence (PL), and photoluminescence excitation (PLE) spectra were used to characterize the prepared samples. The particles were spherical shape and monodispersed. More importantly, the spherical Y 2 O 3 particles were found to have significant changes in size with varying dopant concentration of the Dy 3+ ions, ranging approximately from 550 to 840 nm. The possible growth mechanism of the particles was proposed. Under 349 nm excitation, the crystalline powders exhibited blue and yellow emissions due to the 4 F 9/2 → 6 H 15/2 and 4 F 9/2 → 6 H 13/2 transitions of Dy 3+ ions, respectively. It was further found that with proper Dy 3+ doping concentration, the luminescence color hue was tuned close to the ideal white light with color coordinates of (0.33, 0.33). The submicron-sized Dy 3+ : Y 2 O 3 phosphor is a promising candidate for the white light emitting diodes (WLEDs). [ABSTRACT FROM AUTHOR]

Ce3+-doped Y 2 O 3 -Al 2 O 3 -Sc 2 O 3 ternary ceramics with varying Sc 2 O 3 were prepared via solid-state-reactive method. Their constitutions, crystal structures, microstructures and luminescence properties were thoroughly investigated by powder X-ray diffraction, 45Sc and 27Al solid-state nuclear magnetic resonance (NMR), scanning electron microscope (SEM) as well as photoluminescence (PL) characterizations. Single-phased YSAG transparent ceramics with garnet structure and homogeneous microstructures can be obtained. The NMR results suggest that partial [AlO 6 ] octahedrons are converted into [AlO 4 ] tetrahedrons with increased Sc3+. Partial Sc3+ occupies the remaining octahedral sites, the other Sc3+ occupies the dodecahedral sites. The luminescence spectra of the as-prepared ceramics show broadened emission bands with excessive Sc3+ incorporation. More significantly, the solubility of Ce3+ in garnet ceramics extensively increases due to the incorporation of Sc3+, leading to a considerable red- shift and broadening of emission spectra with little luminescence decline, indicating that the new ceramic phosphors are promising for white- light illumination with improved color rendering index. [ABSTRACT FROM AUTHOR]

Abstract A series of red-emitting Mn4+ doped Lu 3 Al 5 O 12 (LuAG) ceramic phosphors were successfully prepared by a simple solid-state reaction method in a high-temperature muffle. MgO was co-doped as sintering aids and Mg2+ ions helped to realize the charge balance. The relations between the luminescence properties, crystal structures and the microstructures were well established. Results indicated that MgO promoted the densification of the ceramics as the specimens' relative densities were up to 99%. Moreover, the substitution of Al3+ with Mg2+ have changed crystal structures and further affected the luminescent properties. Overall, the obtained ceramic phosphors showed strong red-light emission under excitation of ultraviolet and blue light. By optimizing the Mg2+ and Mn4+ concentration, a quantum efficiency (QE) as high as 47.8% can be achieved under the excitation of 460 nm light, indicating that the LuAG: Mn4+ ceramic phosphors are promising candidates for WLEDs applications. [ABSTRACT FROM AUTHOR]

Abstract: It is interesting that the natural phenomenon of chelator citrate stabilizing nanocrystals in bone could be learned and utilized in manipulating man-made nano-materials. During the synthesis of upconversion luminescent fluorides, it appeared that, the more citrate participated, the more difficult the resultant material transformed from cubic phase KY3F10 nanocrystals, through hexagonal KYF4, to orthorhombic YF3 crystals or mesocrystals, which clearly indicates the critical role of citrate in stabilizing KY3F10 nanocrystals. Particles with different size, morphology, composition, and phase were controlled through the only variation of citric acid content. Meanwhile, the self-assembled mesocrystals showed emergent luminescent property with 63 times higher intensity, compared with the nanocrystals. The same sized YF3 single crystals and YF3 mesocrystals also exhibited dramatic difference in luminescent intensity. [Copyright &y& Elsevier]

Red-emitting ceramic phosphors are significant for warm white light emitting diodes (WLEDs) with high color rendering index (CRI). In this work, Mn doped spinel ceramic phosphors were prepared via high temperature solid-state reaction sintering. The photoluminescence properties of the as-prepared ceramic phosphors were elaborately discussed. The Mn4+ doped spinel ceramics were successfully obtained by incorporating excessive Mg2+ as the charge compensator. They showed red emission peaking at 652 nm under 450 nm excitation. Furthermore, it's exciting to find that the red-emitting ceramic phosphors showed high thermal stability. As operated at 450 K, the emission intensity remained about 66% of the initial intensity operated at room temperature. The results indicate that the Mn4+ doped spinel ceramic phosphors are promising red color converters for warm-WLEDs. • Mn4+ doped red-emitting spinel ceramic phosphors were prepared by solid state reaction method. • The valence states of Mn ions were regulated by tailoring the composition of spinel. • The as-prepared red-emitting ceramic phosphors showed excellent thermal stability. [ABSTRACT FROM AUTHOR]