희토류 이온이 도핑된 K2Ba(WO4)2 형광체의 합성 및 분광학 특성

Abstract

Synthesis and Optical Spectroscopy of Rare-Earth Ions Doped K2Ba(WO4)2 Phosphors

Jae Heung Koo

Department of Physics, The Graduate School, Pukyong National University

Abstract The K2Ba(WO4)2:Ln (Ln = Eu3+, Dy3+, Tb3+, Sm3+) phosphors were synthesized by solid state reaction method at high temperature in the air atmosphere. Crystalline phases of the samples were confirmed by X–ray diffraction analyses. The single phases of K2Ba(WO4)2 are identified and no impurity phases are observed. Luminescence and excited state dynamics of K2Ba(WO4)2:Ln (Ln = Eu3+, Dy3+, Tb3+, Sm3+) phosphors are investigated by optical and laser-excitation spectroscopy at 10 K and room temperature. Emission bands of WO4 centered at 500 nm are observed in the wavelength region 400~600 nm at 10 K in rare–earth doped and undoped K2Ba(WO4)2 phosphors. The WO4 emission intensities decrease and the lifetimes shorten by increasing temperature. The WO4 emission band disappears at room temperature. The excitation spectra of the Eu–doped K2Ba(WO4)2 phosphors exhibit absorption band due to the O2- – Eu3+ charge transfer transition in the wavelength region 220~315 nm and spectral lines due to the 4f – 4f transition in the 350 -500 nm region. The strongest excitation line due to the 7F0 → 5L6 transition is observed at 395 nm. The decay time of the WO4 emission is estimated to be about 28 ㎲ in the undoped K2Ba(WO4)2 phosphor at 10 K. However, the decay time of the WO4 emission in Eu–doped K2Ba(WO4)2 phosphors is longer to be about 67 ㎲. Similar results are observed in the Dy and Sm doped K2Ba(WO4)2 phosphors for which the decay time is estimated about 35 ㎲ at 10 K. The results are attributed to energy migration between RE ions and then back transfer to the WO4 charge transfer state.