Won Bin Im

Tunable full-color-emitting La0.827Al11.9O19.09:Eu2+,Mn2+ phosphor for application to warm white-light-emitting diodes

La0.827Al11.9O19.09:Eu2+,Mn2+ showed three emission bands when excited by ultraviolet light. A blue emission originates from Eu2+, whereas both green and red emissions originate from Mn2+. The luminescent mechanism is explained invoking the energy transfer of Eu2+→Mn2+ and Mn2+(tetrahedralsite)→Mn2+(octahedralsite). This energy transfer was confirmed by faster decay times of the blue and green emissions as energy donors. The emitted color of La0.827Al11.9O19.09:Eu2+,Mn2+ can be easily tailored from blue to red through variations of the Mn2+ content. The white-light-emitting diode fabricated via a combination of an ultraviolet light-emitting diode (λpeak=385nm) with La0.827Al11.9O19.09:Eu2+,Mn2+ showed a warm white light (Tc=3559K).

Red-Emitting LiLa2O2BO3 : Sm3 + , Eu3 + Phosphor for Near-Ultraviolet Light-Emitting Diodes-Based Solid-State Lighting

A red-emitting LiLa 2 O 2 BO 3 :Sm 3+ ,Eu 3+ phosphor has been synthesized and characterized optically for white light-emitting diodes (LEDs). Because the oxyborate group (O 2 BO -7 3 ) can contain high Eu 3+ concentration without concentration quenching, LiLa 2 O 2 BO 3 is a suitable host material for red-emitting phosphor for near-ultraviolet (n-UV) LEDs. When LiLa 2 O 2 BO 3 :Eu 3+ was co-doped with Sm 3+ , emission intensity of Eu 3+ was enhanced by ∼ 30% than that of the sample without Sm 3+ owing to the energy transfer from Sm 3+ to Eu 3+ . This energy transfer was confirmed by faster decay times of Sm 3+ as energy donors. LiLa 2 O 2 BO 3 :Sm 3+ ,Eu 3+ showed a relative brightness of 334.7% of that of Y 2 O 2 S:Eu 3+ , commercial red-emitting phosphor for n-UV LEDs.

Effects of Eu2 + Concentration Variation and Ce3 + Codoping on Photoluminescence Properties of BaGa2S4 : Eu2 + Phosphor

Ba1�x�2yEuxCeyLiyGa2S4 phosphor samples were synthesized by a solid-state reaction method. The lattice parameter of the Ba1�xEuxGa2S4 phosphor samples was linearly decreased from 12.654 to 12.492 A, and the main emission wavelength was shifted from 501 to 530 nm with increase of the Eu 2+ ion concentration x from 0.05 to 0.50. The relative photoluminescence PL intensity under 450 nm excitation was increased with increase of the x from 0.05 to 0.25 due to the excitation band extended to the longer wavelength. However, when x 0.30, the PL intensity was decreased due to nonradiative transitions among the Eu 2+ ions and the formation of EuGa2S4 impurity phase. The Commission International de l’Eclairge chromaticity coordinates were also largely shifted from the bluish-green emitting region x = 0.143, y = 0.506 to the green emitting one x 2.414, y 0.658 by increasing the x from 0.05 to 0.50. The energy transfer from the Ce 3+ ion to the Eu 2+ ion enhanced the PL intensity of the Eu 2+ ion emission under near ultraviolet and blue excitation. The PL intensity of the Ba0.900Eu0.050Ce0.025Li0.025Ga2S4 phosphor sample was higher by 24% than that of the Ba0.95Eu0.05Ga2S4 phosphor sample under 450 nm excitation.

Neutron Rietveld analysis for optimized CaMgSi 2 O 6 :Eu 2+ and its luminescent properties

We optimized synthesis conditions of blue-emitting CaMgSi 2 O 6 :Eu 2+ (CMS:Eu 2+ ) with conventional solid-state reaction and successfully determined structure parameters by Rietveld refinement method with neutron powder diffraction data. The final weighted R -factor R wp was 6.42% and the goodness-of-fit indicator S (= R wp / R e ) was 1.34. The refined lattice parameters of CMS:Eu 2+ were a = 9.7472(3) A, b = 8.9394(2) A, and c = 5.2484(1) A. The β angle was 105.87(1)°. The concentration quenching process was observed, and the critical quenching concentration of Eu 2+ in CMS:Eu 2+ was about 0.01 mol and critical transfer distance was calculated as 12 A. With the help of the Rietveld refinement and Dexter theory, the critical transfer distance was also calculated as 27 A. In addition, the dominant multipolar interaction of CMS:Eu 2+ was investigated from the relationship between the emission intensity per activator concentration and activator concentration. The dipole–dipole interaction was a dominant energy transfer mechanism of electric multipolar character of CMS:Eu 2+ .

Internal pressure effect on cathodoluminescence enhancement of ZnS : Mn2+ synthesized by a sealed vessel

ZnS:Mn 2+ phosphors were synthesized by a modified solid-state reaction method. In the synthesis method, a sealed vessel is used, where heat and pressure are simultaneously utilized. The effects of various synthesis conditions such as temperature, Mn concentration, and pressure on the cathodoluminescence (CL) were investigated. Among them, pressure had an effect on CL property as much as others. It was observed that CL intensities of ZnS:Mn 2+ phosphors increased with the increase of pressure and the best sample showed higher intensity than that of a commercial one by 180%. X-ray diffraction (XRD) and electron paramagnetic-resonance (EPR) were used to understand the enhancement. No change of XRD patterns was observed but the full width at half-maximum (FWHM) of the most intense cubic (111) peak of ZnS:Mn 2+ decreased with the increase of pressure. EPR signal intensity of Mn 2+ increased with the increase of pressure. The improved crystallinity and more substitution of Zn 2+ with Mn metal were believed to be responsible for the enhancement.

P-93: Thermal Stability of (Sr1−x,Bax)3MgSi2O8: Eu2+ Phosphor for Plasma Display Panel Applications

We have synthesized a blue-emitting (Sr1−x,Bax)3MgSi2O8: Eu2+(SBxMS: Eu2+) phosphors with various Ba contents and evaluated their thermal stability. When SBxMS: Eu2+ samples having various Ba contents were baked at 500 °C in air, the large difference in photoluminescence decrease ratio with various Ba contents was observed. From analyses of electron spin resonance on Eu2+ and Rietveld refinement against neutron powder diffraction, the difference in thermal stability of SBxMS: Eu2+ could be ascribed to different Eu2+ sites occupied depending upon amount of Ba substitution. From calculation of the average inter-atomic distance between Eu2+−O (dEu−O) of SBxMS: Eu2+, we confirmed that the dEu-O of different Sr sites may play an important role in thermal stability of phosphors.