L.L. Martín

Whispering gallery modes in a glass microsphere as a function of temperature

Microspheres of Nd3+ doped barium titano silicate glass were prepared and the whispering gallery mode resonances were observed in a modified confocal microscope. A bulk sample of the same glass was calibrated as temperature sensor by the fluorescence intensity ratio technique. After that, the microsphere was heated by laser irradiation process technique in the microscope and the surface temperature was estimated using the fluorescence intensity ratio. This temperature is correlated with the displacement of the whispering gallery mode peaks, showing an average red-shift of 10 pm/K in a wide range of surface temperatures varying from 300 K to 950K. The limit of resolution in temperature was estimated for the fluorescence intensity ratio and the whispering gallery mode displacement, showing an improvement of an order of magnitude for the second method.

Upconversion emission obtained in Yb 3+ -Er 3+ doped fluoroindate glasses using silica microspheres as focusing lens

An intensity enhancement of the green upconversion emission from a codoped Er(3+)-Yb(3+) fluoroindate glass has been obtained by coating the glass surface with silica microspheres (3.8 µm diameter). The microspheres focus an incoming beam (λ ≈ 950 nm) on the surface of the fluoroindate glass. The green emission (λ ≈ 545 nm) of the Er(3+) ions located in the microsphere focus was measured with a microscope in reflection mode, being the peak intensity 4.5 times the emission of the bare substrate. The transversal FWHM of the upconversion spot was experimentally determined by deconvolution with the experimental Point Spread Function of the system, obtaining a value of 309 nm. This value is in good agreement with Finite-Difference Time-Domain simulations taking into account the magnification of the image due to the microsphere.

Optical study of the effect of the impurity content on the ferroelectric properties of Er3+ doped SBN glass-ceramic samples

Photoluminescence measurements have been performed on glass ceramic samples of strontium barium niobate doped with Er3+. The glass-ceramic samples were obtained from the precursor glass by thermal treatment and were doped with different contents of Er3+ ions. The average size of the nanocrystals in the samples was about 50 nm. The optical properties of the Er3+ ions were studied upon 532 nm excitation and the luminescence changes were measured as a function of temperature. The study of the luminescence spectra with increasing temperature has allowed us to ascertain the occurrence of the ferroelectric-paraelectric phase transition in the strontium barium niobate nanocrystals embedded in the glass matrix. We have particularly focused on the temperature range around the Curie temperature, when the system undergoes the transition from the ferroelectric phase to the paraelectric phase. Doping of the strontium barium niobate samples results in a change in the measured value of the Curie temperature which induce...