Realizing a novel dazzling far-red-emitting phosphor NaLaCaTeO6:Mn4+with high quantum yield and luminescence thermal stabilityviathe ionic couple substitution of Na++ La3+for 2Ca2+in Ca3TeO6:Mn4+for indoor plant cultivation LEDs

A novel dazzling far-red-emitting phosphor NaLaCaTeO6:Mn4+ (NLCTO:Mn4+) with superior photoluminescence properties was found via an ionic couple substitution strategy of Na+ + La3+ for 2Ca(2+) in non-luminous Ca3TeO6:Mn4+ for the first time, which is originated from the significant distortion of TeO6 octahedra. The results indicate that the ionic couple substitution strategy is a feasible guide to explore novel Mn4+-involved oxide phosphors for potential application in plant cultivation LEDs

Ca3La2Te2O12:Mn4+,Nd3+,Yb3+ : an efficient thermally-stable UV/visible-far red/NIR broadband spectral converter for c-Si solar cells and plant-growth LEDs

A series of novel Mn4+, Nd3+, Yb3+-doped Ca3La2Te2O12 (CLTO) phosphors were prepared by substituting Te6+ for W6+ in the Ca3La2W2O12 compound using a high-temperature solid-state reaction method. A Mn4+ singly-doped CLTO phosphor (CLTO:0.004Mn(4+)) showed a bright deep red-light emission corresponding to a narrow band around 707 nm (14144 cm(-1)) due to a Mn4+ E-2(g) -> (4)A(2g) spin-forbidden transition upon 365 nm UV excitation, which largely overlapped the absorption spectrum of plant phytochrome P-fr. The excitation spectrum (lambda(em) = 707 nm) presented a broad band ranging from 250 nm (40 000 cm(-1)) to 600 nm (16 667 cm(-1)), which can be decomposed into four Gaussian bands peaking at 318 nm (31 431 cm(-1)), 355 nm (28 148 cm(-1)), 410 nm (24 385 cm(-1)), and 476 nm (20 992 cm(-1)), corresponding to a Mn4+-O2- charge transfer (CT) transition, and Mn4+ transitions T-4(1g) Nd3+ -> Yb3+, was determined based on the simultaneous energy transfer processes Mn4+ -> Nd3+ and Nd3+ -> Yb3+ in the co-doped samples, further enhancing the broadband spectral conversion process of the UV/blue to NIR region, which can be absorbed by photosynthetic bacteria and show high response when applied to c-Si solar cells. More attractively, the luminescence thermal stabilities of both CLTO: 0.004Mn(4+) and CLTO:0.004Mn(4+), 0.04Nd(3+), 0.20Yb(3+) showed excellent performance, and the temperature-dependent luminescence properties of the Mn4+, Nd3+, Yb3+ tri-doped materials have been investigated for the first time. These results indicate that this kind of phosphor can be potentially applied to improving spectral conversion efficiency for c-Si solar cells and plant-growth far-red/NIR LEDs. In addition, this report provides a strategy wherein hosts for Mn4+ doping can be well enriched by substituting Te6+ for W6+ in certain tungstate compounds, which is highly desired in searching for novel red-emitting phosphors

Low-temperature solid-state synthesis and upconversion luminescence properties in (Na/Li)Bi(MoO4)2:Yb3+,Er3+ and Color Tuning in (Na/Li)Bi(MoO4)2:Yb3+,Ho3+,Ce3+ phosphors

In this Article, we reported the synthesis and the upconversion luminescence (UCL) properties of a series of novel (Na/Li)Bi(MoO4)(2):Yb3+,Er3+ [(N/L)BMO:Yb3+,Er3+] and (Na/Li)Bi(MoO4)(2):Yb3+,Ho3+,Ce3+ [(N/L)BMO:Yb3+,Ho3+,Ce3+] phosphors. X-ray diffraction patterns and Rietveld refinements for several representative samples indicated the pure phase of as-prepared samples. The Yb3+,Er3+ codoped (N/L)BMO presented bright green luminescence under 975 nm laser excitation with UCL spectra showing two main green bands around 529 nm (Er3+, H-2(11/2) -> I-4(15/2)) and 551 nm (Er3+, S-4(3/2) -> I-4(15/2)), in addition to a very weak one at 655 nm (Er3+, F-4(9/2) -> I-4(15/2)). The (N/L)BMO:Yb3+,Ho3+ mainly showed a green band around 544 nm (S-5(2),F-5(4) -> I-5(8)) and a red band around 654 nm (F-5(5) -> I-5(8)) upon 975 nm laser excitation. With increasing Yb3+ concentrations in (N/L)BMO:Yb3+,0.01Ho(3+), the red/green ratios decreased monotonously corresponding to the emission color variation from light red to light yellow. Both UCL mechanisms of Yb3+,Er3+ and Yb3+,Ho3+ were determined to be two-phonons absorption processes in (N/L)BMO:Yb3+,Er3+/Ho3+. The Ce3+ ions were introduced into Yb3+,Ho3+ codoped (N/L)BMO to show the color tuning from light yellow to light red originating from the cross relaxation processes of (CR1) Ho3+ (F-5(4), S-5(2)) + Ce3+ (F-2(5/2)) -> Ho3+ (F-5(5)) + Ce3+ (F-2(7/2)) and (CR2) Ho3+(I-5(6)) + Ce3+ (F-2(5/2)) -> Ho3+ (I-5(7)) + Ce3+ (F-2(7/2)), which is based on the energy matching of Ce3+2F7/2-F-2(5/2) level pairs with Ho3+5I6-I-5(7) and F-5(4),S-5(2)-F-5(5) level pairs and confirmed by the decay times. These results suggest good UCL properties of (N/L)BMO:Yb3+, Er3+ and (N/L)BMO:Yb3+, Ho3+, Ce3+ materials, and color modulation is easily controlled by varying Yb3+ concentration and a cross relaxation process between Ce3+ and Ho3+, which provides efficient methods to regulate the emission color of UCL phosphors

Mutual energy transfer luminescent properties in novel CsGd(MoO4)2:Yb3+,Er3+/Ho3+ phosphors for solid-state lighting and solar cells

In this work, we prepared a novel kind of Yb3+, Er3+/Ho3+ co-doped CsGd(MoO4)(2) phosphors with a different structure from the reported ALn(MoO4)(2) (A = Li, Na or K; Ln = La, Gd or Y) compounds using a high-temperature solid-state reaction method. X-ray diffraction showed that the as-prepared samples had a pure phase. Based on the efficient energy transfer from Yb3+ to Er3+/Ho3+, the up-conversion (UC) luminescence of the optimal CsGd(MoO4)(2): 0.30Yb(3+), 0.02Er(3+) sample showed intensely green light with dominant emission peaks at 528 and 550 nm corresponding to Er3+ transitions H-2(11/2)-I-4(15/2) and S-4(3/2)-> I-4(15/2), respectively, as well as a weak emission peak originating from F-4(9/2)-I-4(15/2) at 671 nm, under 975 nm laser excitation. The CsGd(MoO4)(2): Yb3+, Ho3+ samples mainly displayed two emission bands around 540 and 660 nm together with a negligible one at 755 nm, which corresponded to Ho3+ transitions F-4(4),F-5(2)-> I-5(8), F-5(5)-> I-5(8) and F-4(4),F-5(2)-> I-5(7), respectively, under 975 nm laser excitation. With increasing Yb3+ concentration in CsGd(MoO4)(2): Yb3+, Ho3+ phosphors, the emission color could be tuned from orange red to light yellow due to the large energy gap between levels F-4(4),F-5(2) and F-5(5). In addition, the CsGd(MoO4)(2): Yb3+, Er3+ showed green light under 376 nm UV irradiation similar to that upon 975 nm laser excitation. However, the emissions for CsGd(MoO4)(2): Yb3+, Ho3+ samples under 358 nm UV or 449 nm blue excitation showed dominant emission peaks at 540 nm and weak 660 nm and 752 nm peaks, which were a bit different from those under 975 nm excitation. Interestingly, we observed efficient energy transfer phenomena (possible quantum cutting) from Er3+/Ho3+ to Yb3+ and a Yb3+-O2- charge transfer (CT) transition in the molybdates, which was deduced from the visible and near-infrared emission spectra and the decrease of the Er3+/Ho3+ luminescent lifetimes with increasing Yb3+ concentration in the CsGd(MoO (4))(2): Yb3+, Er3+/Ho3+ samples. The luminescence properties of these phosphors suggest their potential possibility for applications in solid-state lighting and displays as well as in c-Si solar energy conversion systems

Majorization algorithms for inspecting circles, ellipses, squares, rectangles, and rhombi

In several disciplines, as diverse as shape analysis, locationtheory, quality control, archaeology, and psychometrics, it can beof interest to fit a circle through a set of points. We use theresult that it suffices to locate a center for which the varianceof the distances from the center to a set of given points isminimal. In this paper, we propose a new algorithm based oniterative majorization to locate the center. This algorithm isguaranteed to yield a series nonincreasing variances until astationary point is obtained. In all practical cases, thestationary point turns out to be a local minimum. Numericalexperiments show that the majorizing algorithm is stable and fast.In addition, we extend the method to fit other shapes, such as asquare, an ellipse, a rectangle, and a rhombus by making use ofthe class of $l_p$ distances and dimension weighting. In addition,we allow for rotations for shapes that might be rotated in theplane. We illustrate how this extended algorithm can be used as atool for shape recognition.iterative majorization;location;optimization;shape analysis

A robust implementation of the Carathéodory-Fejér method

Best rational approximations are notoriously difficult to compute. However, the difference between the best rational approximation to a function and its Carathéodory-Fejér (CF) approximation is often so small as to be negligible in practice, while CF approximations are far easier to compute. We present a robust and fast implementation of this method in the chebfun software system and illustrate its use with several examples. Our implementation handles both polynomial and rational approximation and substantially improves upon earlier published software

Synthesis, structure and luminescence of novel lanthanide containing coordination polymers

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Holmium, thulium and lutetium-octamolybdate [Mo8O28](8-) 1D chains : luminescence investigation of europium doped lutetium-octamolybdate

In this work we report a novel lanthanide octamolybdate 1D chain type of structure formed with holmium, thulium and lutetium. This is a rare case of compounds built out of [Mo8O28](8-) units. These compounds were prepared in a mild reaction synthesis starting from the commonly used heptamolybdate polyoxometalate (POM) [(NH4)(6)[Mo7O24]. Interestingly, in our previous study we have employed a very similar synthesis route for lanthanides with a larger ionic radius and obtained heptamolybdate clusters. For the lanthanides with a smaller ionic radius (Ho3+, Tm3+ and Lu3+) no crystals could be obtained under those conditions. Only when doubling the amount of the lanthanide salt, single crystals suitable for measurements were obtained. These crystals revealed yet a very different structure from those previously observed. Lanthanide octamolybdate 1D chains were formed. Doubling the amount of the salt for other lanthanide ions still yielded heptamolybdate compounds previously reported by us. The lutetium octamolybdate compound was doped with 1-7.5% of Eu3+ ions yielding emission colors ranging from blue to strong red. Additionally in these materials the excitation wavelength was varied, and it was observed that the materials emission color was excitation-wavelength dependent