The unique optical properties of fluorophores nanoparticles doped with rare earth elements have attracted a lot of attention in the scientific community due to their potential application from biological imaging to quantum information.
In this work, we compare the photoluminescence of nanoparticles measured by two different means: traditional objective based microscopy and fiber based optical tweezers.
Our doped NaYF4 nanocrystals are prepared through solvothermal synthesis. Ytterbium and erbium codoping provides nanoparticles with luminescence properties. Under IR laser excitation, the nanoparticles present strong and photostable upconversion signals in the visible range. In addition, by changing the gadolinium content of the host matrix, we obtain nanorods with a controlled aspect ratio up to 20 and a well defined crystalline structure.
The high anisotropy of the nanoparticles results in a strong polarisation of the photoluminescence. To investigate this property, we observed our nanoparticles using a confocal microscope and studied the dependency of the polarisation with the length of the particles.
To complete our characterization, we used optical tweezers to trap nanoparticles in water. We first show the possibility to trap these nanoparticles with an original optical tweezers based on two chemically etched fibers. Due to the optical forces applied by the laser beam coupled into the fibers, the nanorods align themselves between the two fibers along their long axis.
Afterwards, the fibers are not only used to trap the particles but also to collect the luminescence emitted only by the trapped nanoparticles. By this mean, we can analyse the emitted light with a spatial resolution. This result will be compare to previous observation done on the same particles with our confocal microscope.
Moreover, an orthogonal third fiber was implemented in the set up. This fiber can move along the particle and collect the light emitted at different point. We present the link between the photoluminescence properties and the emission point by moving this last fiber.
In addition, our optical tweezers are associated to a traditional objective-based optical microscope. We compared the photoluminescence emitted by particles in a homogeneous medium (water) or at an interface when drop casted on a coverslip.