Absorption and generation of light with silicon nanocrystals in SiO 2 Amsterdam Master of Physics Symposium 2008 Dolf Timmerman Van der Waals-Zeeman Institute University of Amsterdam

Van der Waals-Zeeman Institute | University of Amsterdam Dolf Timmerman Silicon Silicon is a poor light-emitter  Indirect bandgap  Transitions need to overcome Δk  Radiative transitions phonon assisted Amsterdam Master of Physics Symposium 2008 Photonics

Van der Waals-Zeeman Institute | University of Amsterdam Dolf Timmerman Nanocrystals Bandgap modification induced by quantum confinement Bands  quantized energy levels Relaxation of k-vector conservation rule, in relation to indirect bandgap (Heisenberg) Tuning optical properties Silicon 4.3 nm Si NC Amsterdam Master of Physics Symposium 2008

Sample Van der Waals-Zeeman Institute | University of Amsterdam Dolf Timmerman SiO nm Optical active layer containing silicon nanocrystals (and erbium) Sample preparation, Kobe University 2 μm Si - NC Amsterdam Master of Physics Symposium 2008 σ = 14%

Van der Waals-Zeeman Institute | University of Amsterdam Dolf Timmerman ND:YAG LaserOPO Spectro- meter Sample λ = 420 – 660 nm λ = 354 nm 5 ns 10 Hz Room-temperature Setup Amsterdam Master of Physics Symposium 2008

Van der Waals-Zeeman Institute | University of Amsterdam Dolf Timmerman PL measurements Si-NC PL Amsterdam Master of Physics Symposium 2008

Photoluminescence Van der Waals-Zeeman Institute | University of Amsterdam Dolf Timmerman Time integrated PL-spectrum Amsterdam Master of Physics Symposium 2008

Erbium Van der Waals-Zeeman Institute | University of Amsterdam Dolf Timmerman SiO 2 :(Er 3+ +Si NC)  NC absorbs photon  Energy transfer to erbium  Erbium emits at 1.5 μm Si-NC 1.5 μm Er 3+ Amsterdam Master of Physics Symposium 2008 One photon in  one photon out

Van der Waals-Zeeman Institute | University of Amsterdam Dolf Timmerman Energy transfer Amsterdam Master of Physics Symposium 2008

Photoluminescence Er 3+ Van der Waals-Zeeman Institute | University of Amsterdam Dolf Timmerman Time integrated erbium PL flux-dependence Rate equations: In the linear regime: The nr. of emitted photons is proportional to σ PL σ PL is determined from PL intensity flux-dependence Amsterdam Master of Physics Symposium 2008 N Er

Absorption Linear absorption Absorbed fraction: Absorbed photons: Emitted photons: Define relative quantum efficiency: Van der Waals-Zeeman Institute | University of Amsterdam Dolf Timmerman I0I0 I1I1 Amsterdam Master of Physics Symposium 2008

Relative quantum efficiency (η) Van der Waals-Zeeman Institute | University of Amsterdam Dolf Timmerman - η is constant up to a certain photon energy threshold - For larger photon energies a second excitation mechanism takes place Q.E. for different wavelengths in visible and near UV. Amsterdam Master of Physics Symposium 2008

Quantum Cutting detected with Er 3+ Van der Waals-Zeeman Institute | University of Amsterdam Dolf Timmerman Si-NC Er eV Er 3+ Amsterdam Master of Physics Symposium 2008

Van der Waals-Zeeman Institute | University of Amsterdam Dolf Timmerman Si-NC Er 3+ 1 in 2 out Amsterdam Master of Physics Symposium 2008 Quantum Cutting detected with Er3+

η for Er 3+ Van der Waals-Zeeman Institute | University of Amsterdam Dolf Timmerman The quantum cutting process is less efficient for sample with larger NC-Er 3+ distance Two samples - Identical Er 3+ concentration and NC size - Different NC concentration - lower NC concentration  larger average NC-Er 3+ distance Amsterdam Master of Physics Symposium 2008

Van der Waals-Zeeman Institute | University of Amsterdam Dolf Timmerman Amsterdam Master of Physics Symposium 2008 Relative quantum efficiency (η) - η is constant up to a photon energy threshold of ≈ 2E g - For larger photon energies quantum cutting takes place. Q.E. for different wavelengths in visible and near UV.

E ex > 2E G Quantum cutting with Si NCs Van der Waals-Zeeman Institute | University of Amsterdam Dolf Timmerman E ex < 2E G Space-separated quantum cutting (SSQC) Nature Photonics 2, (2008) Amsterdam Master of Physics Symposium 2008

Conclusions  Si NCs can be used to split energy quanta  Erbium ions and neighboring NCs are used to detect this  Space separation in NCs gives long lifetime of excitons, which is desired for applications Van der Waals-Zeeman Institute | University of Amsterdam Dolf Timmerman Amsterdam Master of Physics Symposium 2008

Van der Waals-Zeeman Institute | University of Amsterdam Dolf Timmerman Amsterdam Master of Physics Symposium 2008