Search

In this work, a series of Al2O3–Ce:YAG phosphor powders were synthesized by regulating the excess Al3+ of (Y,Ce)3Al5O12 via coprecipitation method for the first time, where Al3+, Ce3+, and Y3+ elements were uniformly distributed. With the increase of Al3+ content, the morphology of the powders changed from wormlike shapes to flaky shapes, and Y3Al5O12 phases had a tendency to convert to YAlO3 phases. The x wt.% Al2O3–(Y0.999Ce0.001)3Al5O12 (x = 20, 30, 40, 50, 60, and 70) composite phosphor ceramics (CPCs) were obtained by vacuum sintering (1775°C × 10 h), where Al2O3 and Ce:YAG phases were also well‐distributed. When the Al2O3 content was 30–40 wt.%, the average grain size of Al2O3 was close to that of Ce:YAG. A solid‐state laser lighting device was constructed by a 450 nm laser source and CPCs in a reflection mode. By adjusting the laser power, the correlated color temperature (CCT) values of white laser diodes (LDs) were achieved close to the standard white light of 6500 K. Impressively, the white LDs equipped with the 40 wt.% Al2O3‐containing CPCs showed the optimum CCT of 6498 K (color coordinates: 0.31 and 0.38), as well as a high luminous flux of 1169 lm and efficiency of 166 lm/W at the LD power of 7.05 W. This work has provided a potential idea to optimize the composition uniformity of Al2O3–Ce:YAG CPCs as also to explore their excellent performance in the application of white laser lighting. [ABSTRACT FROM AUTHOR]

Introducing Al 2 O 3 as a secondary phase into Ce:LuAG phosphor ceramics has been realized by solid-state reaction method, but there is much room for improvement on the ingredient uniformity and performance of Al 2 O 3 -Ce:LuAG composite phosphor ceramics (CPCs). In this work, the excess of Al3+ in (Ce,Lu) 3 Al 5 O 12 was regulated to synthesize a series of Al 2 O 3 -Ce:LuAG multiphase powders by the co-precipitation method, and homogeneous Al 2 O 3 -Ce:LuAG CPCs (the uniform volume fraction between Al 2 O 3 and Ce:LuAG phases) were obtained by vacuum sintering (1775 °C × 10 h). With an increase in the Al3+ content, the morphology of the multiphase powders changes from small irregular shapes to porous flocs and flakes interwoven, and Lu 3 Al 5 O 12 phases tend to convert to LuAlO 3 phases. When the Al 2 O 3 content is 78–89 mol% in the CPCs, the average grain sizes of Al 2 O 3 are close to those of Ce:LuAG. Among all CPCs with an Al 2 O 3 content of 68–95 mol%, the 85 mol% Al 2 O 3 -Ce:LuAG CPCs initially perform the best in terms of both excitation and emission intensity at room temperature, and their photoluminescence intensities only decrease 4.3% from 25 to 225 °C. A solid-state laser lighting device was constructed by using a 450 nm laser source and Al 2 O 3 -Ce:LuAG CPCs in a reflection mode. The CPCs with 85 mol% Al 2 O 3 content based on 0.9 W laser diodes (LDs) show the optimum luminous flux (LF) and luminous efficiency (LE) of 244 lm and 266 lm∙W−1, respectively. Additionally, the LF of all CPCs based on LDs continues to increase without showing luminescence saturation when the power density increases from 1 to 20 W mm−2. When the 85 mol% Al 2 O 3 -containing CPCs are excited by a 20 W mm−2 LD, the maximum LF reaches 3624 lm, and the LE decreases only by 12.4% (compared to the data under 1 W mm−2 excitation). Al 2 O 3 -Ce:LuAG CPCs have excellent luminescence properties and improved thermal stability, which are promising for the application in solid-state laser lighting. • Excess of Al3+ in (Ce,Lu) 3 Al 5 O 12 was regulated to synthesize multiphase powders by the co-precipitation method. • Al 2 O 3 -Ce:LuAG ceramics with homogeneous biphasic microstructures were sintered by using multiphase powders. • PL intensity of ceramics with 40 wt% Al 2 O 3 content from 25 to 225 °C only decreased by 4.3%. • Excited by the 1–20 W mm−2 LD, ceramics' maximum LF reach 3624 lm, and the LE decreased only by 12.4%. [ABSTRACT FROM AUTHOR]

Yttrium (Y 2 O 3) nanopowders were synthesized via the precipitation method using ammonium hydrogen carbonate (AHC) as the precipitant. The influences of calcination temperature on the composition and morphology of the powders were investigated. Fine Y 2 O 3 powders with low-agglomeration were obtained by calcining the precursor at 1100 °C for 4 h. The primary crystallites were calculated to be ∼47 nm in size and weakly agglomerated to particles with size of ∼79 nm. Using the synthesized powders as the starting materials, Y 2 O 3 ceramics were fabricated by vacuum sintering at different temperatures combined with HIP post-treatment. The densification and micro-structure evolution of the Y 2 O 3 ceramics were systematically investigated. The ceramic sample vacuum sintered at 1500 °C for 2 h and post-HIPed at 1550 °C for 3 h exhibited a uniform and fine microstructure with the average grain of about 1.0 μm. The in-line transmittance of the ceramic sample reached 80.1% at 1100 nm. • Y 2 O 3 transparent ceramics were prepared by two-step sintering from the precipitated nano-powders. • Y 2 O 3 ceramics with the average grain size of 1.0 μm and in-line transmittance of 80.1% at 1100 nm were obtained. • The prepared Y 2 O 3 transparent ceramics are attractive for host materials without any sintering additives. [ABSTRACT FROM AUTHOR]

Ba0.65Sr0.35TiO3-x Bi3NbZrO9(BST-x Bi3NbZrO9, x = 0.5, 1, 3, 5, 7 wt.%) ceramics sintered at low temperature were prepared by traditional solid state reaction method. Influence of Bi3NbZrO9doping amount on the dielectric properties and microstructure of (Ba, Sr)TiO3(barium strontium titanate, BST) capacitor ceramics by means of X-ray diffraction(XRD), Scanning electron microscopy (SEM) and traditional solid state sintering method. The results showed that the impurity materials phase were appeared when Bi3NbZrO9doping amount increased. When Bi3NbZrO9doping amount increased, dielectric constant(ϵr)increased firstly and then decreased and then increased, dielectric loss(tanδ) decreased firstly and then increased, the capacitance temperature changing rate(ΔC/C) decreased. When Bi3NbZrO9doped amount was 1 wt.% and the sintered temperature was 1280°C, the BST ceramics possessed good comprehensive property with ϵrof 2325, tanδ of 0.0048, Ebof 7.8 kV/mm(AC), ΔC/C of −12.9∼14.3% in the temperature range of −30°C∼85°C and the capacitance temperature characteristic was consistent with Y5R. [ABSTRACT FROM PUBLISHER]

(1-x) Ba0.65Sr0.35TiO3-xCaCu3Ti4O12(BST-CCTO) ceramics was prepared by traditional solid-state reaction method, the effect of CaCu3Ti4O12(CCTO) doped on microstructure and phase composition and dielectric properties of BST ceramics were investigated by X-ray diffraction(XRD), scanning electron microscope(SEM) and other analytical methods. The results show that the microstructure and the dielectric properties and the optimum sintered temperature of BST ceramic materials would be greatly affected by the CCTO doped amount. Appropriate doping amount can be fully incorporated into the perovskite lattice of BST and had the excellent performance. While excessive CCTO doping could lead to the appearance of second phase, and the second phase was coexisted with BST in the ceramics. BST ceramics had the optimum properties, ϵrof 1992, tan δ of 0.006, Ebof 5.5 kVmm−1(Alternating Current, AC) and the value of ΔC/C ranges was 13.6% and −14.1% in −55°C∼+125°C temperature range and its capacitance temperature property was suited for X7R, the curie temperature was 15°C and the optimum sintered temperature was 1260°C when CCTO doped amount was 1 wt.%. [ABSTRACT FROM AUTHOR]

Single-phase 2Gd 2 O 3 ·(Gd,Tb) 2 (SO 4) 3 ·nH 2 O precursor with strong crystallinity was synthesized by the water-bath method through optimizing the introducing method of Tb3+ doping, where Tb3+ was introduced from Tb(NO 3) 3. The formation process and phase evolution of the precursor were analyzed in detail. Compared with the conventional method of introducing Tb3+ via Tb 4 O 7 , the inhomogeneous doping caused by the appearance of 2Tb 2 O 3 ·(Gd,Tb) 2 (SO 4) 3 ·nH 2 O in the precursor was avoided. Pure Gd 2 O 2 S:Tb nanopowders with layered structure were obtained after calcination in flowing H 2 -Ar. The Gd 2 O 2 S:Tb powder prepared with Tb(NO 3) 3 has higher XEL intensity than that with Tb 4 O 7. Using the synthesized powders as starting material, Gd 2 O 2 S:Tb scintillation ceramics with high relative density (over 99% of the theoretical value) were fabricated by vacuum pre-sintering and HIP post-treatment in an argon atmosphere. The influences of the introducing method of Tb3+ doping on the microstructure, photoluminescence and X-ray excited luminescence of the Gd 2 O 2 S:Tb ceramics were studied. The ceramic sample prepared with Tb(NO 3) 3 has better luminescence properties due to the homogeneous doping in the ceramics. Temperature-dependent XEL measurements imply that the green emission of the ceramic sample is always dominant with the increase of temperature from 77 K to 340 K, attributed to the cross-relaxation between 5D 3 and 5D 4 levels of Tb3+. • A new introducing method of Tb3+ doping was proposed to optimize the doping uniformity in water-bath method. • Gd 2 O 2 S:Tb nanopowders with good luminescent properties were synthesized by reducing the single-phase precursor. • This method is promising for the preparation of Gd 2 O 2 S ceramics with good scintillation properties. [ABSTRACT FROM AUTHOR]

Terbium aluminum garnet (TAG) transparent ceramics were fabricated by solid-state reactive sintering in vacuum combined with hot isostatic pressing (HIP) post-treatment using tetraethoxysilane (TEOS) as sintering aid. The influences of TEOS amount on the densification, microstructure and optical properties of TAG ceramics were investigated. The in-line transmittance of the TAG ceramic with 0.2 wt% TEOS additive, which was fabricated by pre-sintering at 1700 °C for 20 h and HIP post-treating at 1700 °C for 3 h, can reach about 66% in the visible and near-infrared regions. With appropriate amount of sintering aid, the transmittance of TAG ceramics in the visible wavelength range can be improved significantly by prolonging the holding time. • TAG transparent ceramics were prepared by solid-state reactive sintering and HIP post-treatment. • Influences of TEOS amount on microstructure and optical quality of TAG ceramics were investigated. • Prolonging the pre-sintering time can improve the in-line transmittance of TAG transparent ceramics. [ABSTRACT FROM AUTHOR]

Gd 2 O 2 S:Tb nanopowders were synthesized in hot water-bath with the equal mole ratio of Gd 2 O 3 and H 2 SO 4 as raw materials. The influence of initial bathing temperature of Gd 2 O 3 and H 2 SO 4 , which was defined as initial temperature, on the properties of precursors and powders was investigated. The precursors and Gd 2 O 2 S:Tb powders showed a layered structure, and all the reduced powders exhibit a pure Gd 2 O 2 S phase. With the increase of the initial temperature, the size and thickness of the flakes in the precursors and Gd 2 O 2 S:Tb powders increased. Using the obtained powders as starting materials, Gd 2 O 2 S:Tb scintillation ceramics were successfully fabricated by vacuum pre-sintering at 1250 °C for 3 h, followed by HIP post-treatment at 1450 °C for 3 h. The Gd 2 O 2 S:Tb ceramics from the powders prepared at lower initial temperature show a rapid densification rate during pre-sintering. The Gd 2 O 2 S:Tb ceramics from powders synthesized at 7 °C show the highest optical transmittance and XEL intensity, and the total transmittance of the ceramics with the thickness of 1.0 mm is 25.5% at 545 nm. The microstructures of the Gd 2 O 2 S:Tb ceramics from powders synthesized at different initial temperatures were also studied. • Gd 2 O 2 S:Tb powders prepared at water-bath temperature of 7 °C exhibit the thinnest flake. • Gd 2 O 2 S:Tb ceramics were fabricated by vacuum pre-sintering and HIP post-treatment. • The total transmittance of Gd 2 O 2 S:Tb ceramics from the powders prepared at 7 °C reaches 25.5% at 545 nm. [ABSTRACT FROM AUTHOR]

The 1 at.% Er:CaF 2 transparent ceramics were prepared by the air pre-sintering and hot isostatic pressing (HIP) using nano-powders synthesized by the co-precipitation method. The influence of pre-sintering temperature and HIP post-treatment on the density, microstructures, optical and photoluminescence properties of Er:CaF 2 ceramics were investigated. After HIP post-treatment (650 °C × 2 h, 100 MPa Ar), the pores in the pre-sintering ceramics were gradually eliminated and high transparency was achieved. The maximum in-line transmittance of the HIPed 1 at.% Er:CaF 2 reaches 90.5% at 1600 nm (2.8 mm thickness) when the pre-sintered temperature is 625 °C.The absorption cross section was calculated. The strong absorption peak at 1530 nm reveals an unfavorable infrared emission. The main emission peak at 1530 nm, which is derived from the 4I 13/2 → 4I 15/2 transition of Er3+, can be observed under excitation of 980 nm. Owing to the long lifetime of 4I 13/2 (32.3 ms) and large emission cross section, the 1 at.% Er:CaF 2 transparent ceramics have great potential to achieve a good NIR laser performance in the 1.5 μm region. • Er:CaF 2 transparent ceramics were prepared by air pre-sintering and HIP post-treatment. • Fine-grain Er:CaF 2 transparent ceramics with uniform distribution were obtained. • Er:CaF 2 transparent ceramics showed high in-line transmittance of 90.5% at 1600 nm. [ABSTRACT FROM AUTHOR]