Abnormal co-doping effect on the red persistent luminescence SrS:Eu²⁺,RE³⁺ materials

Area of Science:

• Materials Science
• Solid-State Chemistry
• Luminescence

Background:

• Persistent luminescence (PL) materials are crucial for various applications, but efficient red-emitting options are scarce.
• Strontium sulfide doped with europium (SrS:Eu2+) is a promising candidate for red emission due to its nephelauxetic effect and intrinsic defect generation.
• The weak Sr-S bond in SrS, attributed to soft-hard acid-base interactions, facilitates a high concentration of intrinsic defects.

Purpose of the Study:

• To investigate the efficient preparation and characteristics of SrS:Eu2+,RE3+ materials for persistent luminescence applications.
• To understand the role of intrinsic defects and co-doping on the luminescence properties of SrS:Eu2+.

Main Methods:

• Microwave-assisted solid-state synthesis was employed for material preparation.
• X-ray powder diffraction (XRD) and scanning electron microscopy (SEM) were used for structural and microstructural characterization.
• X-ray absorption spectroscopy (XAS) and electron paramagnetic resonance (EPR) were utilized to analyze the valence state of europium and defect mechanisms.

Main Results:

• SrS:Eu2+,RE3+ materials were successfully synthesized with high crystalline purity and controlled microstructure.
• XAS and EPR revealed significant photo-oxidation of Eu2+ to Eu3+ during X-ray irradiation and excitation.
• An abnormal co-doping effect was observed, with RE2+ energy levels near the conduction band, leading to co-dopant-independent effects.

Conclusions:

• The soft-hard pair host approach in SrS is effective for developing efficient persistent luminescence materials.
• Intrinsic defects and photo-oxidation mechanisms play critical roles in the red-emitting properties of SrS:Eu2+,RE3+.
• Further research into defect engineering in SrS-based materials could lead to advanced red-emitting PL applications.