Figure 5: Optical spectra of HIOS.

(a) Schematics and colour code of the investigated structures: grey (i) bare ZnO/Zn_0.9Mg_0.1O QW structure, blue (ii) HIOS consisting of the QW structure overgrown with 3 nm L4P-sp3, green (iii) HIOS with [RuCp*mes]⁺ interlayer between QW structure and L4P-sp3. (b) Emission and absorption of the isolated individual components. (c) PL decay transients of the QW excitons (T=5 K) of structures (i), (ii) and (iii). Light grey: instrumental response of the time-correlated single-photon counting set-up on the fs excitation pulse. Only the QW is primarily excited. Solid curves are fits to the data by convoluting exponential transients N(t) (with up to three components) with the instrumental response function IRF(t') according to . Lifetimes given in the text are time averages over these decay curves . (d) PL spectra of structures (i), (ii) and (iii). (e) PLE of optimized structure (iii) (detection at the S_1,ν=0–S_0,ν=1 emission peak of L4P-sp3 and low energy side of the QW emission). Yellow: difference spectrum of L4P-sp3 in (iii) and on sapphire. (f) L4P-sp3 PL transients of (ii) and (iii). The excitation photon energy (3.3 eV) is below the ZnO absorption edge, excluding contributions from energy transfer. Evaluation as in (c). Inset: transients of (iii) right after excitation demonstrating the presence of a rise time (dashed curve) for an excitation energy (3.46 eV) above the ZnO optical gap.