This study reports the influence of CdSe–ZnS core–shell quantum dots (QDs) for formation of singlet oxygen using zinc‐phthalocyanine (ZnPc) dyes in colloidal solutions. Using a microluminescence surface scan technique it was possible to measure accurately the photon diffusion length, or photon mean free path, inside the medium. Analyses were performed for a range of QD concentrations. Photon diffusion length was assigned to the bimolecular singlet oxygen emission at 707 nm. Related singlet oxygen emission was predicted by observing quenching of the photon diffusion length measured at the specific oxygen emission as a function of QD concentration, being a nontrivial phenomenon related to the QD donors. Diffusion length measured at 707 nm increased with QD concentration; in the absence of QDs, as in pure ZnPc samples, the emission peak at 707 nm was not observed.

We described a method for the preparation of polydimethylsiloxane (PDMS) phantoms to mimic the optical properties of biologic tissues at distinct wavelengths ranging from the visible to the near-infrared spectra. The present method for fabricating solid optical tissue phantoms using zinc-phthalocyanine chromophores has demonstrated high photostability with optical absorption coefficients up to 1.0  mm, making this phantom proper with absorption bands ranging from 600 to 850 nm. It also happens that the chromophore absorption coefficient is linear as a function of its concentration inside the previous optical window. The optical scattering properties were quantitatively selected by adding TiO particle concentrations to the PDMS phantom. Thus, the quantitative optical properties of absorption and scattering for a large-batch fabrication were demonstrated, making the zinc-phthalocyanine phantoms suitable for use as a reference standard.

The study of the spatial photon migration as a function of the concentration brings into attention the problem of the energy transfer in quantum dot embedded systems. By measuring the photon propagation and its spatial dependence, it is possible to understand the whole dynamics in a quantum dot system, and also improve their concentration dependence to maximize energy propagation due to radiative and non-radiative processes. In this work, a confocal microscope was adapted to scan the spatial distribution of photoluminescence from CdSe-ZnS core-shell quantum dots in colloidal solutions. The energy migration between the quantum dots was monitored by the direct measurement of the photon diffusion length, according to the diffusion theory. We observed that the photon migration length decreases by increasing the quantum dot concentration, this kind of behavior has been regarded as a signature of Förster resonance energy transfer in the system.

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