Preparation and luminescent properties of SrS:Ce by addition of sulphur as a co-activator in SrSO 4 :Ce(SO 4 ) 2 .4H 2 O
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B2.33.1
Preparation and luminescent properties of SrS:Ce by addition of sulphur as a co-activator in SrSO4:Ce(SO4)2.4H2O by carbothermal reduction. P.Thiyagarajan1,2, M.Kottaisamy2, K.Sethupathi1 and M.S. R. Rao1,2* 1
Department of Physics, Indian Institute of Technology-Madras, Chennai – 600 036 Materials Science Research Centre, Indian Institute of Technology, Chennai – 600 036 * also, at Center for Superconductivity Research, Department of Physics, University of Maryland, College Park, MD 20740, USA 2
ABSTRACT
Ce activated SrS has been prepared from SrSO4:Ce(SO4)2.4H2O by ecologically acceptable carbothermal reduction in the absence of inert gas and hazardous H2S environment. The mixtures were fired at 900oC to find out the feasibility of the reduction reaction. In order to understand the compensator behavior we tried with sulfur and various fluxes viz., NH4Cl, NaCl. The materials synthesized were characterized by XRD, photoluminescence emission (PL) and excitation spectroscopy (PLE) and SEM. The characterization results showed the formation of SrS at 900oC with an increase in luminescence intensity after the addition of sulfur as a coactivator. The bright blue-green emission observed at 480nm and 540nm corresponds to energy bands originating from 2T2g (5d) to 2F7/2, 2F5/2(4f) of Ce3+ transitions. The excitation spectrum shows a fundamental absorption of SrS host crystal lattice in the lower wavelength region at 283 nm and Ce at 430 nm. INTRODUCTION The wide band gap semiconductor, SrS doped with Ce3+ has been considered as a promising phosphors to produce blue-green emission for display applications. This phosphor is generally prepared by sulfurizing strontium based sulfate, carbonate etc. at high temperature (>1000oC) in N2 and H2S or CS2 atmosphere. The SrS:Ce3+ phosphors was widely studied to improve the stability against moisture, luminance, luminous efficiency etc. upon doping compensator in relation to its need for electroluminescence (EL), cathodoluminescence (CL) and photoluminescence (PL) [1,2]. However, the information in accordance with energy terms and spectral intensity upon co activator are not yet well understood. The incorporation of Ce3+ ion in crystal lattice splits into two energy levels 4f and 5d and the 4f orbital is electrically screened whereas the 5d orbital splits into eg and t2g levels under the effect of strong Oh crystal field. The luminescence spectra of blue-green emission correspond to the transitions from the lowest excited state 2T2g (5d) to the highest 2F7/2, 2F5/2(4f) state respectively[3-5]. In this work, we are reporting the preparation of SrS:Ce3+ from SrSO4-Ce(SO4)2.4H2O by carbothermal reduction method, and the effect of sulfur and co-activator addition in the host formation and their luminescent properties.
B2.33.2
EXPERIMENTAL DETAILS Phosphor synthesis The host material SrS, was prepared from SrSO4 by solid state carbothermal reduction technique at 900oC for 5h in a single step process without supplying inert gas and H2S stream. We prepared the SrS:Ce3+ phosphors
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