BLUE ELECTROLUMINESCENCE IN SRSO4-CE-BASED THIN-FILMS

A blue electroluminescence (EL) device was fabricated using SrSO4:Ce-b ased phosphor layers deposited by rf sputtering in Ar-H2S atmosphere, Peak emission wavelength was observed at 420 nm corresponding to the e nergy transition from the T-2g(5d) level to the F-5/2(4f) level of Ce ions. This wavelength is shorter than any previously reported. which s uggests that the energy state of the excited 5d electrons is sensitive to the crystal field surrounding Ce ions. A high-resolution two-cryst al X-ray fluorescence spectrometer (HRXRF) was used to examine the com position of the SrSO4-based phosphor layers and chemical state of Cc i ons in them. The chemical state of Cc ions was primarily 3+ in the blu e-green emitting phosphor layers, which were mainly composed of SrS. A n increase in SrSO4 concentration in the phosphor layers leads to a ch ange in the chemical state of Cc ions, resulting in a blue shift in EL emission. A constant high luminance of 5cd/m(2) was obtained under 5 KHz sinusoidal driving. The transferred charge density of the SrSO4:Ce -based EL device was found out to be fairly low compared to the conven tional SrS:Ce EL device.