Energy transfer and a novel SBR thermometry of SrY2O4:Sm3+/Eu3+ phosphor based on redshift of charge transfer band edge

Abstract

In this study, a solid-state reaction was employed to synthesize SrY₂O₄: Sm³⁺, SrY₂O₄: Eu³⁺ and SrY₂O₄: Sm³⁺/Eu³⁺ phosphors. An intriguing redshift phenomenon from charge transfer band (CTB) edge was investigated for single-band ratiometric (SBR) thermometry applications. The phosphors synthesized exhibited an orthogonal CaFe₂O₄ structure with Pnam (62) space group. The Y³⁺ sites from host lattice were most likely to be replaced by Sm³⁺/Eu³⁺ ions. The sample of SrY₂O₄: 0.03 Sm³⁺/0.3Eu³⁺ showed a large degree of agglomeration with elongated particles, having an average size of approximately 4 μm. The energy bandgap decreased due to increased surface imperfections, resulting in enhanced defect level concentration. The dipole-dipole interaction could be used to explain energy transfer (ET) of Sm³⁺-Sm³⁺ and Sm³⁺-Eu³⁺. Furthermore, the energy transfer (ET) efficiency of Sm³⁺→Eu³⁺ in Sr₂YO₄ reached 77.7 %. The sample exhibited a good thermal stability (90.956 %@423 K) with E_a of 0.31 eV, which was an important parameter for broadening thermometry range. A thermometry strategy utilized this redshift phenomenon from CTB edge with anti-thermal quenching behavior and other peaks or bands with thermal quenching was therefore proposed. The high S_r value of 1.533 % K⁻¹@298 K provides a great potential for optical thermometry application, contributing significantly to the advancement of single band ratiometric thermometry technologies.