Neutron Rietveld analysis for optimized CaMgSi 2 O 6 :Eu 2+ and its luminescent properties
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Yong-Il Kim Korea Research Institute of Standards and Science, Yuseong, Daejeon 305-600, Republic of Korea
Jong Hyuk Kang and Duk Young Jeona) Department of Materials Science and Engineering, Korea Advanced Institute of Science and Technology, Daejeon 305-701, Republic of Korea
Ha Kyun Jung and Kyeong Youl Jung Advanced Materials Division, Korea Research Institute of Chemical Technology, Yuseong-gu, Daejeon 305-600, Republic of Korea (Received 15 February 2005; accepted 7 April 2005)
We optimized synthesis conditions of blue-emitting CaMgSi2O6:Eu2+ (CMS:Eu2+) with conventional solid-state reaction and successfully determined structure parameters by Rietveld refinement method with neutron powder diffraction data. The final weighted R-factor Rwp was 6.42% and the goodness-of-fit indicator S (⳱ Rwp/Re) was 1.34. The refined lattice parameters of CMS:Eu2+ were a ⳱ 9.7472(3) Å, b ⳱ 8.9394(2) Å, and c ⳱ 5.2484(1) Å. The  angle was 105.87(1)°. The concentration quenching process was observed, and the critical quenching concentration of Eu2+ in CMS:Eu2+ was about 0.01 mol and critical transfer distance was calculated as 12 Å. With the help of the Rietveld refinement and Dexter theory, the critical transfer distance was also calculated as 27 Å. In addition, the dominant multipolar interaction of CMS:Eu2+ 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:Eu2+.
I. INTRODUCTION
BaMgAl10O17:Eu2+ (BAM) is an efficiency blue phosphor for plasma display panels (PDPs) because of its high luminescence under vacuum ultraviolet (VUV) excitation. However, the luminance decrease and color shift of this phosphor that occur during the baking process are well known problems. The thermal degradation of the phosphor that occur during the baking process is a particularly serious problem for manufacturing of PDP panels. It has been reported that the thermal degradation of BAM is probably related to the change of either the valence of Eu2+ to Eu3+ or its crystal structure (alumina), which has an open layer in the crystal.1–3 Based on this information, CaMgSi2O6:Eu2+ (CMS:Eu2+) has been proposed as a way to overcome the drawbacks of BAM because it is more stable under the baking process and has relatively good photoluminescence (PL) a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2005.0253 J. Mater. Res., Vol. 20, No. 8, Aug 2005
properties under VUV excitation.2,3 However, the PL intensity of CMS:Eu2+ excited by 147 nm sources is weaker than that of BAM, and the study on crystal structure of CMS:Eu2+ also has not been done sufficiently. To obtain CMS:Eu2+ phosphor of high luminescence efficiency, we have optimized it in terms of factors such as activator concentration, gas flow rates, and SiO2 ratios. Since, in 147 nm excitation, the excitation wavelength is shorter than absorption edge of the host lattice, the V
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