Luminescence of Pb²⁺ Centers in SrS and SrSe Phosphors

Abstract

The emission and excitation spectra of the SrS: Pb²⁺ and SrSe: Pb²⁺ phosphors were measured at low temperatures. The ³A_1u→¹A_1g emission band at 374 or 392 nm is observed at 80 K in addition to the ³T_1u→¹A_1g emission band at 368 or 383 nm for SrS: Pb²⁺ or SrSe: Pb²⁺, respectively. On these emission bands, phonon structures appear at 6 K. The zero-phonon line on the ³A_1u→¹A_1g emission band grows under the external magnetic field. The sharp excitation band observed at 351 nm for SrS: Pb²⁺ or at 368 nm for SrSe: Pb²⁺ at 80 K is assigned to the A band in the isolated Pb²⁺ center. The excitation mechanism in the high energy region is explained as the transfer of the excitation energy from the host crystal to an unexcited Pb²⁺ ion. It is confirmed that the rigid rotator model which explains admixture between the ³T_1u and ³A_1u states is also available for the complex Pb²⁺(S²⁻)₆ or Pb²⁺(Se²⁻)₆ in these phosphors.