Search

A series of Eu-doped LaSr 2 AlO 5 phosphors were synthesized by high-temperature solid state reactions under oxidative and reductive atmospheres, respectively. The photoluminescence properties, fluorescence quenching mechanism and valence-change behavior of europium ions in the phosphor have been studied. For the samples prepared in oxidative atmosphere, the Eu 3+ ions occupy the La 3+ sites and exhibit characteristic sharp lines(500–750 nm) originating from the 5 D 1 and 5 D 0 levels to 7F transitions. With the increase of Eu 3+ concentration, the chromaticity coordinates of La 1− x Sr 2 AlO 5 : x Eu 3+ phosphors are turned from (0.479, 0.453) for x =0.005 to (0.621, 0.358) for x =1.0. The quenching process of 5 D 1 → 7 F 1 (533 nm) emission is attributed to cross-relaxation as the Eu 3+ concentration reaches 5 mol%. The dominant line emission 5 D 0 → 7 F 2 (619 nm) is quenched due to the exchange interaction as the Eu 3+ concentration reaches 75 mol%. For the sample prepared in reductive atmosphere, it shows the presence of both Eu 3+ and Eu 2+ . The Eu 2+ in LaSr 2 AlO 5 host lattice can be excited by a blue light with an intense broad red emission band centered at 610 nm (a full width at half maximum of 110 nm) with color coordinates of (0.611, 0.368). The internal quantum efficiency was measured to be ~42%, indicating that this phosphor has a great potential in blue-chip pumped white light emitting diodes (WLEDs). The conditions for the reduction process of Eu 3+ to Eu 2+ in solid state compounds were discussed. From the X-ray diffraction and Gaussian fitting of the emission spectra, we propose that Eu 3+ ions occupy the La 3+ sites while Eu 2+ ions occupy the two different Sr 2+ sites. [ABSTRACT FROM AUTHOR]

Abstract: Single-phase broad-band red-emitting Ca3Si2O7:Eu2+ phosphors, with photoluminescence features that qualify them as candidates for white light-emitting diodes applications, were successfully synthesized via a modified solid-state reaction method that employed H3BO3 as a flux. The phosphors produced have an intense broad red emission band, with a peak at 603nm, a full width at half maximum of 110nm, and color coordinates of (0.550, 0.438). Concentration quenching occurred at 0.01mol Eu2+. The discussion of the results shows that Eu2+ ions should be accommodated at the Ca-sites of the lattice, dipole–dipole interactions should predominantly govern the energy transfer mechanism among them, and the critical distance between them is ∼31Å. [Copyright &y& Elsevier]

Abstract: Divalent europium-activated strontium orthosilicate Sr2SiO4:Eu2+ and Mg0.1Sr1.9SiO4:Eu2+ phosphors were synthesized through the solid-state reaction technique. Their luminescent properties under ultraviolet excitation were investigated. The X-ray diffraction (XRD) results show that these phosphors are of α′-Sr2SiO4 phase with a trace of β-Sr2SiO4. Doping of Eu2+ ion into the crystal lattice results in the lattice constant being expended, while Mg2+ makes the lattice constant shrinking. A solid solution with the same crystal structure is formed when Eu2+ or Mg2+ substitutes part of Sr2+ ions and occupies the same lattice sites. The Sr2SiO4:Eu2+ phosphors show two emission spectra peaked at 535 and 473nm originated from the 5d–4f transition of Eu2+ ion doped in two different Sr2+ sites in the host lattice. By substitution of 0.1mol of Sr2+ with Mg2+, these two emission bands are tuned to be in the blue and yellow region (459 and 564nm for Mg0.1Sr1.88SiO4:Eu0.02), respectively. The tuning effect is discussed. With a combination of the blue and yellow emission bands the phosphors show white color, indicating that these phosphors may become promising phosphor candidates for white light-emitting diodes (LEDs). [Copyright &y& Elsevier]

Phosphor layers are of vital importance for the development of advanced phosphor-converted light-emitting diodes (LEDs). However, owing to the fixed ratio of red-green-blue (RGB) phosphors, it has been difficult for the RGB phosphor layers with conventional structure to tune light emission colours. Herein, we have experimentally fabricated nine types of phosphor layers with patterned RGB pixel array, which consist of tuneable RGB ratio in a planar configuration. Moreover, we carried out optical simulation based on Monte-Carlo theory to assist in adjusting the light-emission colours and the corresponding chromaticity coordinates. The simulations were further verified by the experimental results via samples fabricated by the stencil printing technique. In accordance with the nine types of phosphor layers with patterned pixel arrays in various RGB ratios, we have finally obtained corresponding nine light-emission colours for the applications of LED light emission decoration. These designed advanced pixel-array phosphor layers demonstrate great potential for applications in decorated light emission and display devices with significant implications for industrial improvement in these research areas. • Nine patterned phosphor layers can realize nine output light colours. • With increasing mixing time of RGB phosphors, more output light colours of phosphor layers can be obtained. • The pixel-array phosphor layers was prepared via stencil printing method which is suitable for a large-scale production. [ABSTRACT FROM AUTHOR]

Phosphor layer are essential in the application of phosphor-converted white light emitting diodes (pc-WLEDs). However, the conventional structure of red–green–blue (RGB) phosphor layers can cause severe re-absorption of blue light, resulting in low luminous efficiency and colour rendering index (CRI). In this paper, we fabricated a new WLEDs phosphor layer, which consisted of patterned RGB phosphor pixel arrays in a planar configuration, by the stencil printing technique. Optical simulation based on Monte-Carlo theory has been applied to assist designing the optimal pattern of the phosphor pixel arrays. By tuning the layout of the pixel arrays and the size of phosphor pixels, we achieved uniform output white light with high luminous intensity of 1.47 × 109 cd and CRI of 95.6, which are superior compared with the intensity of 1.11 × 109 cd and CRI of 93.5 obtained from WLEDs with conventional dispensing phosphor layer. Our newly-designed phosphor pixel-array layer possesses great potential for applications in advanced lighting and display devices with vast implications for industrial improvement in these research areas. [ABSTRACT FROM AUTHOR]

A multicolour LED is a miniaturized, long-lasting, and easy-to-achieve colour adjustable emission light source. It is widely used in outdoor displays and room lighting fields. However, the increase in the cost and the decrease in luminous efficiency when adjusting lighting colours have constrained the development of multicolour LEDs. In this study, we initially designed a phosphor conversion pixel array through optical simulation and then prepared the phosphor conversion pixel arrays with different layouts using a semi-cured template method. Finally, we packaged the phosphor conversion pixel array with the blue LED array as a remote phosphor LED. The measurement of the luminous performance indicated that the colour gamut of multicolour LEDs was included in the simulated colour gamut, and the colour of the light was consistent with the design guidelines. Notably, the multicolour LED emission efficiency packaged with a phosphor conversion pixel array could reach 125 lm/W, and the hexagonal phosphor conversion pixel array had better emission performance than the square phosphor conversion pixel array. • Based on the Monte Carlo principle, multicolour LEDs composed of array phosphor-converted film and blue-LED chip are designed. • Phosphor-converted pixel arrays are prepared by semi-cured template method with high moulding quality. • By comparing the experimental and simulation results, colour-tuneable characteristics of the multicolour LEDs is verified. • The luminous efficiency of multicolour LEDs reach up to 125.0 lm/W and changing pixel can reduce the secondary reabsorption of fluorescence. [ABSTRACT FROM AUTHOR]

Abstract: Ba2+-doped Sr2SiO4:Eu2+ phosphors were synthesized with the high-temperature solid-state reaction technique. The experimental results, summarized in the successful production of a single-phase powder with fine microstructure of spherical particles with smooth surface, suggest that Ba2+-doping favors the stabilization of α′-Sr2SiO4. Rietveld refinement of X-ray diffractograms suggests that Ba2+ and Eu2+ ions occupy the sites of Sr2+ in the lattice of α′-Sr2SiO4. The produced phosphors show two intense emission bands at green and yellow regions of spectrum, originated from Eu2+ ions accommodated at two different sites in the host crystal, whose peaks depend on the concentrations of Ba2+ and Eu2+. Intense and broad excitation spectra extend from ultraviolet to the blue region. [Copyright &y& Elsevier]

YAG:Ce3+ yellow phosphor are particularly used luminescent materials to produce white light in phosphor-converted white LED (pc-WLED). Surface coating of YAG phosphor is the main concern for desired optical performance of the phosphors. Many scholars conducted various experimental analysis on the surface coating of phosphors to improve yellow emission, but the theoretical explanation by which phosphor coating could help improving light efficiency has not yet been studied. In this paper, based on Mie theory, the optical constants such as scattering coefficient, absorption coefficient and asymmetry parameter of YAG:Ce3+ phosphor and YAG@SiO 2 (YAG:Ce3+ phosphor surface coated with nano-SiO 2 layer) were calculated. An optical configuration of chip scale packages (CSP) WLED was constructed by coupling YAG:Ce3+ or YAG@SiO 2 phosphors with a LED laser. Based on the optical parameters calculated by Mie theory, the luminescent properties of YAG:Ce3+ and YAG@SiO 2 WLED were simulated by Monte Carlo method. The results showed that a thin SiO 2 coating layer on YAG phosphor result in an overall increase in luminous performances compared with original YAG WLED. The absorption coefficient of phosphor is the main concern affecting the light emission in WLED. Due to the fact that YAG@SiO 2 possess higher 460 nm absorption coefficient (460 μ a b s) , it could absorb more blue light than YAG, thereby it has a 1.2% higher conversion efficiency than YAG, finally the enhanced luminous efficiency of YAG@SiO 2 WLED is obtained. The results obtained in this work provides a potential method in future WLED packaging designing. • We improve the overall light extraction efficiency from the perspective of adjusting the structure of a single phosphor particle. • The optical constants of YAG phosphor and YAG@SiO 2 (YAG surface coated with nano-SiO 2 layer) were calculated based on Mie theory. • The luminescence performances of YAG and YAG@SiO 2 CSP WLED were simulated, the results showed that the absorption coefficient of phosphor is the main concern affecting the light emission in WLED. [ABSTRACT FROM AUTHOR]