Internal pressure effect on cathodoluminescence enhancement of ZnS:Mn 2+ synthesized by a sealed vessel
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W.B. Im Department of Materials Science and Engineering, Korea Advanced Institute of Science and Technology, Yuseong-gu, Daejeon 305-701, Republic of Korea
W.J. Chung Department of Advance Materials Engineering, Kongju National University, Kongju-city, Chungnam 314-701, Republic of Korea
H.S. Seo and J.T. Ahn IT Convergence & Components Laboratory, Electronics and Telecommunications Research Institute, Yuseong, Daejeon 305-600, Republic of Korea
D.Y. Jeona) Department of Materials Science and Engineering, Korea Advanced Institute of Science and Technology, Yuseong-gu, Daejeon 305-701, Republic of Korea (Received 22 January 2007; accepted 7 June 2007)
ZnS:Mn2+ 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:Mn2+ 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:Mn2+ decreased with the increase of pressure. EPR signal intensity of Mn2+ increased with the increase of pressure. The improved crystallinity and more substitution of Zn2+ with Mn metal were believed to be responsible for the enhancement.
I. INTRODUCTION
A lot of attention has been paid on ZnS-based materials for various applications such as display, solar cell, and infrared windows because of their large band-gap energy of 3.66 eV, direct recombination properties and high resistance to electric field.1–3 ZnS:Mn2+ has been extensively studied as a phosphor material for its exceptional electroluminescent (EL) and cathodoluminescent (CL) properties. As for the EL application, ZnS:Mn2+ phosphor has been mostly used as an active layer of both thin-film and powder-type electroluminescent devices driven by alternating or direct current.4,5 Many efforts a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2007.0354 2838
J. Mater. Res., Vol. 22, No. 10, Oct 2007
have been made to enhance its EL property as well as CL via codoping with sensitizer, surface coating, and so on.6,7 Conventional sulfide phosphors are normally prepared by the sulfurization of the corresponding oxides or carbonates with highly purified H2S or CS2 gas, which are very toxic and expensive. When CS2 gas is used, impurity phases that reduce luminescent property can be made. These sulfide phosphors are also prepared by reacting the corresponding oxides or carbonates with sulfur and flux such as Na2CO3 and K2CO3. In this method, impurity phases can be also made and it i
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