Strain effects on the optical parameters of quantum dots nanocrystals employed in biomedical applications

Abstract

The purpose of this study was to perform the influence of the strain (lattice and radius) effects on the optical parameters of nanocrystals for use in medical imaging instrumentation technology. The present manuscript involved (a) quantum dots (QD) based nanophosphors with particle size 3–5nm in diameter, (b) dielectric constants (core) of nanophosphors in the range 2–4, and (c) the whole portion of the electromagnetic spectrum visible to the human eye, 400–700nm. Lattice strain effects on the optical properties were evaluated by the modification of the bulk dielectric function using a Drude–Sommerfeld model for the free or conduction electrons, and a core term representing the bound electrons. The Mie scattering theory, was used to predict the shifted optical parameters. Results showed that (i) lattice stain reduces the real part (n) of refractive index, (ii) the reduction of n becomes higher with the increase of εcore(ω) and (iii) no significant variations on n were observed under the variability of incident light wavelength (400–700nm). Light wavelength was found to affect significantly the imaginary part (k) of the complex refractive index. In addition, the radius strain (i) decreases the light extinction coefficient, mext, (ii) increases the anisotropy factor, g and (iii) increases the light absorption probability, p. However, in cases of εcore(ω)=2, radius strain of 5% seems to present slightly higher p values than the cases of radius strain 10%. The present investigation found that the modification on the optical parameters enhances the utilization of quantom-dots luminescent nanomaterial in optical diffusion studies with requirements of high sensitivity (such as nuclear medical imaging modalities) rather than of high light spatial resolution (such as X-ray projection medical imaging systems).