The II-VI binary chalcogenide semiconductor-based quantum dots (Q-dots) dispersed in a glass matrix was first reported in 1981 by Ekimov et al.1 Since then, Q-dots embedded in glass matrices have attracted significant attention for optoelectronic and spectroscopic applications by tailoring the optical, electronic and environmental durability properties. For example, the Q-dots are more stable in glass hosts than that formed from the solution or powder nanoparticles routes. Furthermore, the discrete electron and hole pair states in Q-dot structures are generally observed due to the strong quantum confinement effect, which is size-dependent and offers tuneability of spectroscopic and optical properties. Amongst the known Q-dots structures, the II-VI binary chalcogenide semiconductors Q-dots based on cadmium chalcogenides (e.g. CdS) has a narrow optical bandgap and strong photoluminescence emission from the visible to NIR wavelengths.

We have studied the spectroscopic properties of Dy3+-ion doped CdS Q-dots in glass and analysed the energy transfer mechanism between the Q-dots states and the 4f-4f/5d-4f states in Dy3+ ions. We synthesised CdS-doped and Dy3+-ion-doped CdS Q-dots in the borosilicate-based glasses using conventional melting and quenching techniques. The nominal composition (wt%) of borosilicate glass was 50SiO2-10Na2O-6MgO-12K2O-10ZnO-6B2O3-4TiO2-(2-x)CdS-xDy2O3, [where x=0, 0.25 and 0.50 wt% of Dy3+]. About 50g batch of borosilicate glass, one with CdS and the other with CdS-Dy3+-doped Q-dots, was melted in an alumina crucible between 900oC and 1250°C for about 4 hours in the air. The homogenised molten glass was poured into a preheated brass mould at 550oC and left for annealing before switching off the annealing furnace after an hour so that the annealed glass cooled slowly to room temperature. The annealed samples were polished, cut, and heat treated at 550o, 575o and 600oC for 6 hours to investigate the growth behaviour of CdS- and CdS-Dy3+ion doped Q-dots. The absorption spectra of as-prepared and heat-treated samples were collected using a UV–visible spectrophotometer in the wavelength range of 250–2500 nm for characterising the bandgap edge and optical transitions in CdS- and CdS-doped with Dy3+-ion glass samples. The semiconductor Q-dots grown in the glass matrix were characterised using Raman spectroscopy and X-ray diffraction analyses. The photoluminescence emission and lifetime properties of as-prepared and heat-treated samples were measured using 450 nm and 800 nm excitation sources. The PL spectra in the visible-to-NIR transitions from the CdS Q-dots and Dy3+ were analysed based on the energy transfer mechanism, and relaxation lifetimes are reported.

Figure 1: Spectroscopic properties of CdS- and CdS-Dy3+ion doped borosilicate Q-dots glasses (a) optical bandgap tunability and (b) Enhancement in the photoluminescence emission when excited with a 450 nm source.

References

Ekimov, A. I.; Onushchenko, A. A., Quantum Size Effect in Three-Dimensional Microscopic Semiconductor Crystals. JETP Lett. 1981, 34, 345-348.