Recombination emission in the phosphor CaSO4-Pb2+

Abstract

Optical methods were used to investigate the formation of combined or induced electronic emissive states in irradiated CaSO₄-Pb²⁺ phosphor at 2.9 eV and 3.1 eV. The combined electronic emissive state consists of electronic states of impurity Pb+-SO₄^- and intrinsic SO₄^3--SO₄^-  trapping centers. The impurity electronic states are formed by capturing free electrons of conduction band  by Pb²⁺ impurities and  localizing electrons resulting from charge transfer from the excited anion complex SO₄^2-(O^2--Pb²⁺) impurities by  reaction  Pb²⁺+(e^-+SO₄^-)→Pb⁺-SO₄^-. The intrinsic electronic states are formed by capturing free electrons of conduction band by anion complexes or by localizing electrons resulting from charge transfer from the excited anion complex SO₄^-(O^2--SO₄^2-) to neighboring anion complexes by reaction SO₄^2-+(e^-+SO₄^-)→SO₄^3--SO₄^-. The combined electronic emissive states at 2.9 eV and 3.1 eV are excited by photons of 3.9-4.0 eV and 4.5 eV. It was also experimentally shown that in the phosphor with induced trapping centers, recombination emissions at 3.1 eV and 2.9 eV are regenerated upon excitation by photons of 3.9-4.0 eV and 4.5 eV. Thus, energies of 3.9-4.0 eV and 4.5 eV are the excitation and absorption energies between the electronic and hole trapping centers located in the transparency region of CaSO₄-Pb²⁺ phosphor.