Particle size control of a monodisperse spherical Y 2 O 3 :Eu 3+ phosphor and its photoluminescence properties
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A monodisperse spherical Y2O3:Eu3+ phosphor was prepared by a homogeneous precipitation method. The mean size of the phosphor particles (MSPP) was successfully controlled by changing the volume ratio of normal alcohol (RA) (propanol) in the solvents mixed between deionized water and normal propanol. When the RA was increased from 0 to 0.7, the MSPP decreased while maintaining a high yield of >95%. Although the prepared phosphor samples were fired at the same temperature, the thermal energy was delivered more efficiently into the inner side of the phosphor particles with the decrease of the MSPP. Therefore, the crystallinity and also the photoluminescence (PL) intensity of the phosphor increased with the decrease in the MSPP. In addition, because the numbers of Eu3+ ions located near the particle surfaces increased with the decrease of particle size, the ratio of PL intensity caused by the 5D0–7F2 transition to that caused by 5D0–7F1 transition increased from 10.8 to 12.7 with the decrease in MSPP.
I. INTRODUCTION
Nowadays, high-definition display has been one of the most interesting topics in flat-panel display (FPD) industry. To increase the resolution of a screen, the pixel size of the screen has been continuously reduced. Recent advances in high-definition display have placed some requirements on the development of corresponding phosphors. For application in high-definition displays with small-sized pixels, phosphors with a small size and narrow size distribution are required. A uniform size for the phosphor particles helps to form a uniform thickness of a phosphor layer, and thus their luminescence distribution can be uniform on a whole phosphor screen.1,2 In addition, phosphor particles should have a spherical shape and high luminescence efficiency. Phosphor particles with a spherical shape are capable of minimizing light scattering on their surfaces. Consequently, the efficiency of light emission and the brightness of a phosphor screen are expected to be improved.3,4 Another feature of spherical phosphor particles is they can be packed more densely than ones with a different shape so that a dense phosphor layer can be formed by using the spherical phosphor particles.5–7 On the other hand, shape and size, and thus lumines-
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Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2007.0257 J. Mater. Res., Vol. 22, No. 7, Jul 2007
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cent properties, of phosphor particles are strongly affected by the synthesis methods used. It is difficult to control the shape and size of phosphor particles with a conventional solid-state reaction method that requires a high-temperature firing process for a long time as well as mechanical milling processes. Therefore, phosphor particles prepared using a solid-state reaction method have irregular shape and surface damage, which act as a nonradiative transition center and cause a decrease of luminescence efficiency.8 Recently, a spray-pyrolysis method has been recommended as a promising method
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