We evaluated the damage caused to optically trapped red blood cells (RBCs) after 1 or 2 min of exposure to near-infrared (NIR) laser beams at 785 or 1064 nm. Damage was quantified by measuring cell elasticity using an automatic, real-time, homemade, optical tweezer system. The measurements, performed on a significant number (hundreds) of cells, revealed an overall deformability decrease up to ∼104% after 2 min of light exposure, under 10 mW optical trapping for the 785-nm wavelength. Wavelength dependence of the optical damage is attributed to the light absorption by hemoglobin. The results provided evidence that RBCs have their biomechanical properties affected by NIR radiation. Our findings establish limits for laser applications with RBCs.
In this report the optical properties and energy-transfer frequency upconversion luminescence of Er3+/Yb3+-codoped
laponite-derived powders under 975 nm infrared excitation is investigated. The 75%(laponite):25%(PbF2) samples
doped with erbium and ytterbium ions, generated high intensity red emission around 660 nm and lower intensity green
emission around 525, and 545 nm. The observed emission signals were examined as a function of the excitation power
and annealing temperature. The results indicate that energy-transfer, and excited-state absorption are the major
upconversion excitation mechanism for the erbium excited-state red emitting level. The precursor glass samples were
also heat treated at annealing temperatures of 300 °C, 400 °C, 500 °C, and 600 °C, for a 2h period. The dependence of
the visible upconversion luminescence emission upon the annealing temperature indicated the existence of an optimum
temperature which leads to the generation of the most intense and spectrally pure red emission signal.
There has recently been a great deal of interest in searching for new materials for application as hosts in infrared-tovisible
light upconverters or optical amplifiers based upon rare-earth doped systems. Some of their many applications
include: color displays, high density optical recording, biomedical diagnostics, infrared laser viewers and indicators,
fiber lasers and amplifiers. Fluorosilicate based sol gel glass ceramics have recently emerged as auspicious candidates
for such photonic devices applications. These glasses are advantageous because they present low temperature of
preparation, better mechanical strength, chemical durability, and thermal stability than fluoride-based glasses. The
present work involves the investigation of optical transitions and upconversion fluorescence spectroscopy of trivalent
lanthanide ions Er3+ codoped with Yb3+ in β-PbF2 nanocrystals dispersed in silica glassy matrix, excited with nearinfrared
diode lasers. The dependence of the upconversion luminescence upon diode laser power, and the upconversion
excitation mechanisms involved are also investigated.
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