ABSTRACT
The intentional design of rare earth doped luminescent architecture exhibits unique optical properties and it can be considered as a promising and potential probe for optical imaging applications. Calcium fluoride (CaF2) nanoparticles doped with optimum concentration of Nd3+ and Yb3+ as sensitizer and activator, respectively, were synthesized by wet precipitation method and characterized by x-ray diffraction (XRD) and photoluminescence. In spite of the fact that the energy transfer takes place from Nd3+ to Yb3+, the luminescence intensity was found to be weak due to the lattice defects generated from the doping of trivalent cations (Nd3+ and Yb3+) for divalent host cations (Ca2+). These defect centres were tailored via charge compensation approach by co-doping Na+ ion and by optimizing its concentration and heat treatment duration. CaF2 doped with 5 mol% Nd3+, 3 mol% Yb3+ and 4 mol% Na+ after heat treatment for 2 h exhibited significantly enhanced emission intensity and life time. The ex vivo fluorescence imaging experiment was done at various thickness of chicken breast tissue. The maximum theoretical depth penetration of the NIR light was calculated and the value is 14 mm. The fabricated phosphor can serve as contrast agent for deep tissue near infrared (NIR) light imaging.
Subject(s)
Metals, Rare Earth , Nanoparticles , Fluorescent Dyes , Luminescence , X-Ray DiffractionABSTRACT
There is increasing interest in rare earth (RE) doped nanoparticles (NPs) due to their sharp absorption and photoluminescence (PL) in the near infrared (NIR) spectral region. These NIR based nanoparticles (NPs) could allow biological imaging at substantial depths with enhanced contrast and high spatial resolution due to the absence of auto fluorescence in biological samples under infrared excitation. Here, we present the highly efficient infrared photoluminescence in GdF3:Nd(3+) nanoparticles under 800 nm excitation within the hydrodynamic size limitations for bio-applications. The downconversion (Stokes emission) absolute quantum yields (QY) in powder, polymaleic anhydride-alt-1-octadicene (PMAO) coated powder and colloidal solutions have been investigated. QY measurements have revealed that downconversion (Stokes emission) QYs of approximately 5 ± 2 nm sized GdF3:1% Nd(3+) colloidal NPs are 2000 times higher than those of efficient upconversion (UC) particles NaYF4:20% Er/2% Yb of the same size. Furthermore, the utility of these NIR emitting nanoparticles for bioimaging probes has been demonstrated by confocal imaging and spectroscopic study.
Subject(s)
Fluorides/chemistry , Gadolinium/chemistry , Microscopy/methods , Nanoparticles/chemistry , Neodymium/chemistry , Absorption , Animals , Cell Line , Cell Survival , Colloids/chemistry , Fibroblasts/cytology , Fluorescence , Hot Temperature , Hydrogen-Ion Concentration , Infrared Rays , Luminescence , Mice , Microscopy, Confocal , Nanotechnology , Particle Size , Photochemistry , Powders , Spectroscopy, Near-Infrared , X-Ray DiffractionABSTRACT
The optical properties of melanin have been characterized for a number of laser wavelengths in the visible region. The index of refraction of melanin is measured by the conventional method of minimum deviation using a hollow quartz prism at these wavelengths. The inverse adding doubling method based on the diffusion approximation and radiative transport theory have been employed to determine the absorption, scattering, and scattering anisotropy coefficients of melanin from the measurements of diffuse transmission, diffuse reflection and collimated transmission using double integrating spheres. The results obtained by the use of inverse adding doubling method have been compared to the Monte Carlo simulation technique.
