Enhanced photo-luminescence of CdX (X= S, Se, Te) Q-dots embedded in ordered mesoporous silica thin films

DIEGO ONNA; MARÍA LUZ MARTÍNEZ RICCI; ALDABE BILMES, SARA

kyoto

Congreso; XVIII International Sol-Gel Conference; 2015

Photo-luminescence (PL) of Q-dots can be tuned by the particle diameter, crystallinity and surface states (SS). In particular, SS exhibit as recombination centers providing a non-radiative emission or as a radiative decay at longer wavelengths, far from the excitonic emission. In this work we explore the formation and the PL of Q-dots grown in ordered mesoporous oxides (OMPO) where pores act as true nanoreactors leading to confined quasi-spherical nanoparticles (NPs) whose size is limited by pore diameter fixed by the molecular template.OMPO films were prepared following the conventional protocols[1], using different amphiphillic templates to tune pore radios (3-9nm). Q-dots were grown by successive impregnations in 0,1M Cadmium Acetate solutions and an X precursor solution. Samples were characterized by UV-Vis, SEM, HRTEM, and Environmental Ellipsometric Porosimetry (EEP). Steady state PL was measured at different excitation wavelengths in order to get the maximum intensity for each system. PL spectra of Q-dots in SiO2-OMPO may exhibit excitonic bands. At higher wavelengths one or two PL bands appear which are assigned to bulk defects (BD) ?i.e. anion vacancies- or to SS. These bands intensity depends on the activation by illumination (Figure 1). Irradiation (280nm≤ λI ≤ 380 nm) for less than 10 min leads to a noticeable increase of BD PL. Further irradiation promotes a BD-excitonic interconversion. The spectra recorded after 2 days in the dark does not show changes contrary to the fast decay present in Q-dots in suspensions.In summary, inclusion of CdX Q-dots in SiO2-OMPO films gives persistent enhanced PL of Q-dots tuned by the pore diameter and to provides an environmental friendly platform for the design of optical devices based on Q-dots.