16.40 o4 s janssens

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Research 3: S Janssens

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16.40 o4 s janssens

  1. 1. Nanocrystals for optical amplificationS. Janssens1,2, G. Williams2, D. Clarke1 and S. G. Raymond1 1 Industrial Research Ltd, P.O. Box 31310, Lower Hutt, New Zealand. Victoria University, P.O. Box 600, Wellington, New Zealand. 2 1
  2. 2. Nanoparticles• Optical amplifiers • Necessary part for optical systems • Compensate losses • PMMA bands• Why nanoparticles? • Incorporating in polymers → ease of processability • Limited scattering • Doped with luminescent ions → low phonon energy host matrix → decreases quenching • Optical properties size dependent • Stable 2
  3. 3. NanoparticlesRare earth ions: Quantum dots:• Used in many applications: • Still being developed: • Optical amplifiers (EDFA) • Optical amplifiers • Lasers • Lasers • Phosphors • Phosphors • Scintillators • Bio-markers • Etc. • Etc.• Luminescence of trivalent rare • Luminescence characterised earth characterised by: by: • Long lifetimes (μs-ms) • Short lifetimes (ns-μs) • Low oscillator strength • High oscillator strength • Narrow emission bands • Broad emission bands • Independent of size • Tuneable emission • Problems: • Auger recombination 3 • Transient absorption
  4. 4. Quantum dots• Semiconductor nanocrystals• Properties size and shape dependent – Exciton bohr radius > QD radius – Quantum confinement of e and h in 3 dimensions – Discrete atomic like energy levels – Larger bandgap 4
  5. 5. Quantum dots• CdSxSe1-x• Tunable – Size – Composition – x larger at surface → gradient• h confined in core• Overlap e and h wavefunction → splitting dark-bright excitons 5
  6. 6. Structural CharacterizationSample x x Particle size (nominal) (EDS) (nm) • Zinc-blende structure A 0.96 0.69 3.07 • Size XRD and TEM comparable B  0.98 0.65  2.3 C 0.980 0.78 4.65 • PMMA composites 0.25% wt D 0.992 0.90 4.0 E 0.993 0.91 5.11 6 F 1 1 4.48
  7. 7. Optical properties • Quantum confined states • Scattering and absorption in PMMA composites • Blue shift with sulfur concentration • Composition effect > size effect 7
  8. 8. Optical properties in solution • QY decreases with x τexp increases than decreases • Combined effect of increase in τrad and decrease in τnrad • τnrad decreases due to decreasing energy barrier • longer τradτexp= QY τrad = (τ-1rad+τ-1nrad )-1 8
  9. 9. Optical properties in PMMA• Red shift in time in PMMA• Not in solution• Forster Energy transfer• Clustering• x larger → shift smaller → transfer between QD with different composition 9
  10. 10. BaMgF4 nanoparticles• BaMgF4 ferroelectric crystal• 2nd order nonlinear material• Doped with luminescent ions• Synthesised using reverse microemulsion 10
  11. 11. XRD and TEMOrthorhombic BaMgF4Scherrer equation → 12 nmClusters → 0.5-2 μm long and 0.2-0.3 μm wide 11Rods → 50-80 nm long and 10-15 nm wide
  12. 12. Clustering• Particle have permanent dipole moment• Align along electric field lines of dipole 12
  13. 13. Optical properties• Doped with luminescent ions -TM ions -RE ions• Good luminescence• QY Eu3+ 45% at RT 13
  14. 14. Poling• Transparent PMMA films• usefull 2nd order material → non centro-symmetric• Random orientation → Centro-symmetric → no 2nd order nonlinear effects→ Aligning necessary• Applying high electric field (~50V/μm) → Heating to Tg• Relative change in diffraction intensities• (h00) lines stronger, (00l) lines weaker→ partial alignment→ clusters hinder alignment 14
  15. 15. Conclusion• QY of QD ~30% and decreases with x• Shift in wavelength mainly due to change in composition• Clustering in PMMA composites, but still good transparancy• Synthesizing BaMgF4 nanoparticles• Good luminescence for doped BaMgF4 particles• Possible to partially align particles using electric field• Potential for optical amplification and EO devices 15
  16. 16. Thanks for your attention Questions? 16

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