Influence of Sm3+ concentration on structural and spectroscopic properties of orange-red emitting PbWO4 phosphor: An energy transfer study

In this work, various concentrations of Sm3+ activated PbWO4 phosphors were prepared by a simple hydrothermal method with particles exhibiting dendrite-like microstructures. XRD patterns and Micro-Raman spectra confirmed that the PbWO4 microcrystals crystallized in a scheelite-type tetragonal structure. X-ray photoelectron spectroscopy (XPS) was carried out to confirm the oxidation states of various constituents and dopant element and also the presence of oxygen vacancies. A shift in optical band gap values towards lower energy could be observed with increase in Sm3+ content in PbWO4 matrix. Photoluminescence and decay lifetime results indicate that excitation at charge transfer band (O2- -> W6+/Sm3+) at 320 nm is more efficient than Sm3+ direct excitation at 403 nm to give the dominant emission of Sm3+ at 643 nm. The interaction between Sm3+ ions which leads to concentration quenching as the amount of Sm3+ ions increases was confirmed as a dipole-dipole type and critical distance R-c was found to be 15.08 angstrom. From the CIE study, these phosphors show a good orange-red colour and might serve as a candidate for applications in solid-state lighting fields.