This document discusses using nanocrystals for optical amplification applications. It describes doping nanoparticles like quantum dots and rare earth ions into polymer matrices for use in optical amplifiers. Quantum dots can be tuned by size and composition to emit light at different wavelengths. Rare earth ions in nanocrystals have narrow emission bands and long lifetimes. The document also discusses synthesizing barium magnesium fluoride nanoparticles doped with luminescent ions and partially aligning them using an electric field for potential use in optical amplification and electro-optic devices.

1. Nanocrystals for optical
amplification
S. Janssens1,2, G. Williams2, D. Clarke1 and S. G. Raymond1
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Industrial Research Ltd, P.O. Box 31310, Lower Hutt, New Zealand.
Victoria University, P.O. Box 600, Wellington, New Zealand.
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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
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3. Nanoparticles
Rare 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
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• Transient absorption

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
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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
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6. Structural Characterization
Sample 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
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F 1 1 4.48

7. Optical properties
• Quantum confined states
• Scattering and absorption in
PMMA composites
• Blue shift with sulfur concentration
• Composition effect > size effect
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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 τrad
τexp= QY τrad = (τ-1rad+τ-1nrad )-1
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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. BaMgF4 nanoparticles
• BaMgF4 ferroelectric crystal
• 2nd order nonlinear material
• Doped with luminescent ions
• Synthesised using reverse microemulsion
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11. XRD and TEM
Orthorhombic BaMgF4
Scherrer equation → 12 nm
Clusters → 0.5-2 μm long and 0.2-0.3 μm wide
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Rods → 50-80 nm long and 10-15 nm wide

12. Clustering
• Particle have permanent dipole moment
• Align along electric field lines of dipole
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13. Optical properties
• Doped with luminescent ions
-TM ions
-RE ions
• Good luminescence
• QY Eu3+ 45% at RT
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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
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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
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16. Thanks for your attention
Questions?
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