P. Haro-González

High‐Sensitivity Fluorescence Lifetime Thermal Sensing Based on CdTe Quantum Dots

The potential use of CdTe quantum dots as luminescence nano-probes for lifetime fluorescence nano-thermometry is demonstrated. The maximum thermal sensitivity achievable is strongly dependent on the quantum dot size. For the smallest sizes (close to 1 nm) the lifetime thermal sensitivity overcomes those of conventional nano-probes used in fluorescence lifetime thermometry.

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.

Whispering-gallery modes in glass microspheres: optimization of pumping in a modified confocal microscope

Whispering-gallery modes (WGMs) on Nd3+-doped glass microspheres with a radius of ∼15 μm were measured in a modified confocal microscope, where a dual spatial resolution in both excitation and detection zones was possible. As an alternative to the standard excitation mechanism by an evanescent wave, we used an efficient pumping/detecting scheme, focusing a laser in the microsphere and exciting the Nd3+ ions, whose fluorescent emission produces the WGMs. We have also measured the generated WGMs by changing the detection zone, where higher amplitude resonances were found when exciting in the center and detecting at the edge of the microsphere.

Nanocrystals distribution inside the writing lines in a glass matrix using Argon laser irradiation

Localized modification in strontium barium niobate glass doped with Ho(3+) under laser irradiation has been carried out. The preliminary samples of this study have been fabricated by the melt quenching method and doped with 2.5% mol of Ho(3+). A 3.5W cw multiline Ar-laser has been focused and shifted in a line during laser irradiation. The formation of Strontium Barium Niobate nanocrystals has been confirmed by X-ray diffraction, atomic force microscope image and fluorescence. They have been localized in the irradiation line and change the optical properties of the sample. These nanocrystals have been obtained due to the excitation of the Ho(3+) ions which under nonradiative processes produced the heating of the sample. In this work, it has been demonstrated that the diffusion of the Nb(5+) ions to the border of the irradiated line controls the growth of the nanocrystals in the sample.

Laser irradiation in Nd3+ doped strontium barium niobate glass

A local nanocrystalline formation in a neodymium doped strontium barium niobate (SBN) glass has been obtained under argon laser irradiation. The intense emission around 880 nm, originated from the F43/2 (F45/2) thermalized level when the glass structure changes to a glass ceramic structure due to the irradiation of the laser beam, has been studied. The intensities and lifetimes change from this level inside and outside the irradiated area made by the laser excitation. They have been analyzed and demonstrated that the desvitrification process has been successfully achieved. These results confirm that nanocrystals of SBN have been created by the laser action confirming that the transition from glass to glass ceramic has been completed. These results are in agreement with the emission properties of nanocrystals of the bulk glass ceramic sample. The present study also suggests that the SBN nanocrystal has a potential application as temperature detector.

Stimulated emission in the red, green, and blue in a nanostructured glass ceramics

Red, green, and blue stimulated emissions have been achieved in Ho3+ doped oxyfluoride glass ceramic at room temperature. The material shows three emission bands at the red (650 nm), green (545 nm), and blue (488 nm) regions under infrared excitation at 750 nm. These emission bands are caused by a photon avalanche upconversion process previously reported. A pump and probe experimental setup has been designed to show stimulated emissions at the three bands. The pump power threshold for positive gain in the 490 nm band has been estimated around 2.7 kW/cm2. Higher thresholds are expected for the other bands.

Optical amplification in Er3+-doped transparent Ba2NaNb5O15 single crystal at 850 nm

Positive optical gain around 5 cm−1 (∼21 dB/cm) has been observed in Er3+-doped Ba2NaNb5O15 single crystal using a pump and probe experimental setup. High power laser pulses at 532 nm have been used as the pump source in order to strongly populate the S43/2(H211/2) levels of the Er3+ ions due to ground state absorption. Low signal beam cw laser radiation at 850 nm has been used as the probe beam to stimulate the emission associated with the S43/2(H211/2)→I413/2 electronic transition of the Er3+ ions. The process has been modelized as a four level system, and its population has been analyzed and simulated in order to study the gain dynamics. Optical amplification of the probe signal has been observed during the first 60 μs, which represents a good agreement between the measured lifetime of the S43/2(H211/2) levels and the reported simulation.

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...

Control of the local devitrification on oxyfluoride glass doped with Er3+ ions under diode laser irradiation

Temperature control of the devitrification process in an erbium doped oxyfluoride glass under laser irradiation is reported. The green upconversion emissions around 525 and 545 nm originated from the thermalized H211/2 and S43/2 levels were studied when the glass structure changes to glass ceramic during irradiation with a laser beam. Power dependence of the fluorescence intensity ratio was used to determine the temperature of the irradiated zone. The transition from glass to glass ceramic takes place under 2300 mW of laser power with an estimated temperature around 783 K. This result agrees with the one obtained in the samples devitrified under conventional furnace treatment. Therefore, the estimation of the temperature of the irradiated zone through the fluorescence intensity ratio method allows a controlled devitrification. Moreover, an irradiated line has been written in the glass showing an important diffusion of the Pb2+ and F− ions. These results confirm that nanocrystals have been created due to t...