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- 1. Excitons and traps in rare-earth materials probed by a free-electron laser Michael F Reid Jon Wells, Pubudu Senanayake Alex Salkeld, Roger Reeves Giel Berden, FELIX Andries Meijerink, Utrecht Chang-Kui Duan, USTC, China NZIP, Wellington, October 18, 2011
- 5. Filling of orbitals s s p d f
- 7. 4f N : Sharp-line spectra
- 8. Vibrations
- 9. Bonds are like springs Equilibrium Change in electronic state can change spring constant New equilibrium
- 11. Conduction Band, Free Electrons, Excitons Conduction Band Valence Band 4f 5d
- 12. Excitons: Can be “free”… Ours are “bound”
- 14. SrCl 2 :Yb 2+ : Sánchez-Sanz et al. J. Chem. Phys. 133, 114509 (2010) Yb 2+ Cl - /F - Sr 2+ /Ca 2+ Sr Cl 2 : Yb 2+ / Ca F 2 : Yb 2+
- 15. SrCl 2 :Yb 2+ 4f 14 4f 13 5d (mixed) 4f 13 6s Sánchez-Sanz et al. J. Chem. Phys. 133, 114509 2010 bond length 4f 13 5d (E) 30000 cm -1 Exciton state forms as excited electron becomes delocalized and bonds shorten
- 16. SrCl 2 :Yb 2+ Absorption “ Normal”Emission
- 17. CaF 2 :Yb 2+ Absorption “ anomalous” Emission 4f 14 4f 13 5d 4f 13 +e ? τ rad =15ms τ rad =260μs
- 18. FEL Excited State Absorption UV Laser Exciton emission IR FEL 4f 13 5d 4f 14 4f 13 +e 40cm -1 τ rad =15ms τ rad =260μs
- 19. FELIX Nieuwegein, Netherlands
- 20. FELIX Synchonized UV laser + FEL UV IR
- 22. UV + FEL + Emission Spectrometer UV IR Emission
- 23. 1kHz ps UV 10 Hz 6 μ s IR macropulse UV IR Emission 365 nm 12.1 µ m 825 cm -1 Lowest state τ rad =15ms !
- 24. 10K Time-resolved spectrum Shift similar to temperature Probably same emission
- 25. 12.1 µ m 825 cm -1 16 µ m 625 cm -1 Faster emission from higher exciton state More sites radiating
- 26. Scan IR 12.1 µ m 825 cm -1 16 µ m 625 cm -1
- 27. Integrate over time to obtain spectrum
- 29. Electron Trap Liberation? Long-time enhancement must be trap liberation Coulomb trap model
- 30. Localized Mobile
- 31. Applications of Traps X-ray storage phosphors Persistent Luminescence
- 32. SrF 2 :Yb 2+ Larger lattice, lower energy. SrF 2 :Yb 2+ CaF 2 :Yb 2+
- 33. CaF 2 :Yb 2+ SrF 2 :Yb 2+
- 34. Trap Liberation in SrF 2 :Yb 2+ Effective even after exciton decay UV IR Exciton ESA + Trap Liberation Only Trap Liberation 200μs 400μs 600μs 800μs
Notas do Editor
- E state has shorter bond length than ground state. T2 longer. Can tell from pressure experiments, etc.
- UV laser at left goes through wall. Felix is synchronized with the UV laser UV 1kHz, Felix 10Hz macropulses.
- With ratio we get spectrum. High-energy from january with caf2 windows. I cut it off at 10microns, where it starts to dip. Medium with PbS windows Low with polypropolene windows and different FEL. Medium energy range is probably saturated.
- Cubic, so MD allowed (or vibronic). The calculation is oscillator strength. The normalization of the excitation spectrum has not been worked out yet.