Probing electron transfer processes in YPO(4):Ce, Sm by combined synchrotron-laser excitation spectroscopy

Area of Science:

• Materials Science
• Solid-State Physics
• Luminescence and Spectroscopy

Background:

• Yttrium phosphate co-doped with cerium (Ce) and samarium (Sm) functions as a charge storage phosphor.
• High doping levels (0.5%) in these phosphors lead to defect proximity, causing uncontrolled non-radiative charge loss via tunneling.
• Understanding these defects and their interactions is crucial for optimizing phosphor performance.

Purpose of the Study:

• To characterize defects in co-doped yttrium phosphate.
• To investigate mutual defect interactions and intra-pair charge transfer routes.
• To determine energy levels within the bandgap and the conduction band energy of YPO(4).

Main Methods:

• Utilized a laser probe (2.8 eV) during synchrotron luminescence excitation.
• Employed two experimental modes: quasi-equilibrium charge population probing and dynamic direct electron transfer probing.
• Monitored Ce(3+) 5d-4f emission while probing Sm(2+) ions.

Main Results:

• Determined the conduction band energy of YPO(4) to be 9.20 eV.
• Positioned Sm(2+) and Ce(3+) ground state energies within the bandgap at 6.8 eV and 3.85 eV above the valence band, respectively.
• Precisely measured the energy difference between Sm(2+) and Ce(3+) ground states as 2.98 eV.

Conclusions:

• Characterized defect interactions and charge transfer pathways in highly doped yttrium phosphate phosphors.
• Provided accurate energy level information crucial for understanding charge storage and loss mechanisms.
• Demonstrated the utility of combined laser probing and synchrotron excitation for defect analysis in phosphors.