Xuanyi Yuan

Enhanced Luminescence Performances of Tunable Lu3–xYxAl5O12:Mn4+ Red Phosphor by Ions of Rn+ (Li+, Na+, Ca2+, Mg2+, Sr2+, Sc3+)

A novel red-emitting Lu3Al5O12:Mn4+ (LuAG:Mn4+) phosphor was synthesized by a solid-state reaction. The emission-band position is shifted to red region by gradually increasing the amount of substitution of Lu3+ for Y3+, eventually yielding fully Y3Al5O12:Mn4+ (YAG:Mn4+). The compared structural and optical properties of the phosphors were investigated. From the experimentally measured spectroscopic data, crystal field parameter Dq and Racah parameters B and C are calculated to be 2127, 1464, and 3620 cm-1 in LuAG:Mn4+, respectively. In YAG:Mn4+, Dq, B, and C are calculated to be 2082, 1524, and 3740 cm-1, respectively. Impressively, Ca2+/Li+/Mg2+/Sr2+/Sc3+/Na+ dopants were found to be beneficial for enhancing Mn4+ luminescence, and the related mechanisms were systematically discussed.

M8MgSc(PO4)7:xDy3+ (M = Ca/Sr) Single-Phase Full-Color Phosphor with High Thermal Emission Stability

Two series of phosphors of Ca8MgSc(PO4)7:Dy3+ and Sr8MgSc(PO4)7:Dy3+ single-phase white-emitting phosphors with high thermal emission stability are synthesized by the high-temperature solid-state reaction. The crystal structure, photoluminescence (PL), PL excitation (PLE), and thermal PL quenching spectra of Ca8MgSc(PO4)7:xDy3+ and Sr8MgSc(PO4)7:xDy3+ were investigated and compared in detail. Upon excitation at 387 nm, M8MgSc(PO4)7:xDy3+ (M = Ca/Sr) showed white emission centered at 480, 571, 660, and 754 nm. The white-emitting Dy-phosphor Ca8MgSc(PO4)7:Dy3+ (CMSP:Dy) had good terminal stability. The emission intensity of Ca8MgSc(PO4)7:Dy3+ still remained 95.2% of that at room temperature at 160 °C, and remained 77.3% at 300 °C under 387 nm excitation.

Effect of starting composition and post-anneal on the structure and luminescence properties of Eu-doped Ca-α-SiAlON phosphors prepared by combustion synthesis

Abstract Eu-doped Ca-α-SiAlON yellow phosphors, with the compositions Ca0.72Eu0.08Si9.56Al2.44O0.84N15.16, were prepared by a highly efficient combustion synthesis method. By optimizing the starting compositions of reactants and choosing appropriate post-annealing conditions, phase-pure, uniform and fine Ca-α-sialon:Eu2+ phosphors possessing the particle size ranging ∼3–5 μm, and good luminescence properties with an intense emission band that peaks at 592 nm under n-UV or blue light excitation were obtained. The results indicated that combustion synthesis method was an energy efficient, time saving and low cost way to prepare Ca-α-SiAlON phosphors by controlling the mass ratio of comburents. A combination with post-annealing treatment was desired for further increase of the properties of Ca-α-SiAlON phosphors.

Strongly enhanced luminescence of Sr4Al14O25:Mn4+ phosphor by co-doping B3+ and Na+ ions with red emission for plant growth LEDs

Development of a more cost-effective radiation source for use in plant-growing facilities would be of significant benefit for commercial crop production applications. A series of co-doped B3+ and Na+ ions Sr4Al14O25:Mn4+ inorganic luminescence materials which can be used for plant growth were successfully synthesized through a conventional high-temperature solid-state reaction. Powder X-ray diffraction was used to confirm the crystal structure and phase purity of the obtained samples. Then scanning electron microscopy elemental mapping was undertaken to characterize the distribution of the doped ions. Detail investigations on the photoluminescence emission and excitation spectra revealed that emission intensity of tetravalent manganese ions can be well enhanced by monovalent sodium ions and trivalent boron ions under near-ultraviolet and blue excitation. Additionally, crystal field parameters and energies of states are calculated and discussed in detail. Particularly we achieve a photoluminescence internal quantum yield as high as 60.8% under 450 nm blue light excitation for Sr4Al14O25:Mn4+, Na+, B3+. Therefore, satisfactory luminescence properties make these phosphors available to LEDs for plant growth.

Longitudinally diode-pumped planar waveguide YAG/Yb:LuAG/YAG ceramic laser at 1030.7 nm.

Composite YAG/15 at. % Yb:LuAG/YAG transparent ceramic planar waveguide was fabricated by a tape casting method and vacuum sintering technology. Under a 970 nm diode laser pumping, the absorbed efficiency of 85.4% was achieved, and efficient CW laser operation at 1030.7 nm was accomplished with a good beam quality with Gaussian spatial profile. A maximum output power of 288 mW was obtained under a pump power of 4.69 W, corresponding to a slope efficiency of 9% and an O-O conversion efficiency of 5%.

Energy transfer properties and enhanced color rendering index of chromaticity tunable green-yellow-red-emitting Y 3 Al 5 O 12 : Ce 3+ , Cr 3+ phosphors for white light-emitting diodes

White light-emitting diodes using YAG: Ce3+ phosphors suffer from the deficiency of red component, leading to a low color rendering index (CRI) and a high correlated color temperature (CCT). Herein, a yellow-red single-phase YAG: Ce3+, Cr3+ phosphor was synthesized by a traditional solid-state reaction. Compared with Cr3+ ion single-doped YAG phosphor, the emission intensity in the far-red region of the co-doped YAG: Ce3+, Cr3+ sample increases because of the energy transfer from Ce3+ ions to Cr3+ ions. For sample Y3Al5O12: 0.02Ce3+, 0.008Cr3+ phosphor, the internal and external quantum efficiencies are 58.9% and 46.7%, respectively. And, the fabricated white LED shows a CCT of 6085 K at CIE 1931 coordinate (0.3208, 0.3273). Moreover, the CRI is as high as 77.9 while that of the corresponding Ce3+ single-doped YAG phosphor is only 63.2. Thus, the Ce3+ and Cr3+ co-doped YAG phosphors are suitable for white light-emitting diodes (WLEDs).

Investigation on transition behavior and electrical properties of (K0.5Na0.5)1-xLixNb0.84Ta0.1Sb0.06O3 around polymorphic phase transition region

(K0.5Na0.5)1-xLixNb0.84Ta0.1Sb0.06O3 (KNLNTS) lead free ceramics with different Li concentration were fabricated by conventional solid-state reaction method. By increasing Li ions in KNLNTS, the grains grow up and the crystal structure changes from orthorhombic to tetragonal. When 0.03 ≤ x ≤ 0.05, the ceramics structure lays in PPT region. Polarization versus electric field (P-E) hysteresis loops at room temperature show good ferroelectric properties and the remnant polarization decreases by increasing Li content while coercive electric keeps almost unchanged. In PPT region, taking x = 0.04 as an example, the sample shows excellent dielectric properties: the dielectric constant is 1159 and loss tangent is 0.04, while the piezoelectric constant d33 is 245 pC/N and kp is 0.44 at room temperature, it is promising for (K0.5Na0.5)1-xLixNb0.84Ta0.1Sb0.06O3 with 4 at. % Li to substitute PZT.