In this work, the existence of different crystal field sites for the rare-earth-doped tin dioxide nanopowder and RE-doped SiO2-SnO2 glass-ceramics is investigated. The slightly different crystal field symmetries have been resolved by using site-selective fluorescence line-narrowing spectroscopy. The obtained results show that a variety of optically non equivalent sites exist for the europium ion in the tin dioxide oxide structure associated to different allowed positions of the oxygen vacancies, whereas additional spectral disorder is found in the case of the glass-ceramic matrix. Ultrafast spectroscopy performed on Eu3+-doped tin dioxide nanocrystals shows that host-rare earth energy transfer occurs at a transfer rate of about 1.5×106 s-1. Similar experiments carried out for the Er3+-doped glass-ceramic system also validate the hypothesis that both host and matrix-excited RE emissions are decoupled due to the different origins of the involved physical mechanisms.
A detailed investigation of the dependence of the real time luminescence of Eu3+-doped tin dioxide nanopowders on rare earth site symmetry and host defects is given. Ultrafast spectroscopy shows that host-rare earth energy transfer occurs at a transfer rate of about 1.5×106 s-1, whereas the intrinsic broad band SnO2 emission has a very short build up time, of the order of 60 ps, and a lifetime of hundreds of picoseconds. These results validate the hypothesis that both host and matrix-excited RE emissions are decoupled due to the different origins of the involved physical mechanisms.
The present work displays a thorough study of the optical spectroscopy of multilevel RE-doped tin oxide nanocrystals. Our study provides the structural grounds about the behavior of the RE emission under site-selective excitation as well as the capability of the host to hold the RE ions at the nanocrystal lattice sites and, as a consequence, the possibility to reach the RE excited states by direct host excitation.
Gadolinium oxysulfide crystal is a wide-gap semiconductor material known as an excellent host for trivalent rare-earth ions. The present investigation explores the upconversion and thermal properties of Er3+-doped Gd2O2S crystal powders as well as their potentiality for anti-Stokes cooling. A detailed study of the wavelength and pumping power dependence of the spectroscopic properties and temperature field for samples of various erbium concentrations is presented.
The present investigation explores the upconversion properties of Er3+- doped La2O2S crystal powder as well as its potentiality for anti-Stokes cooling. A detailed study of the wavelength and pumping power dependence of the spectroscopic properties and of the temperature field of samples with various erbium concentrations is presented. The analysis of both spectroscopic and thermal measurements shows that after a transient heating induced by the background absorption, cooling can be attained by means of anti-Stokes processes.
One- and two-photon pumped random lasing have been demonstrated in a powder based on a Rhodamine B-doped diureasil
hybrid by using a picosecond pump laser emitting either at 532 nm or 1064 nm under controlled experimental
conditions. In both cases, we have used the same diffusive medium with identical spatial disorder, the same time-width
and temporal profile for the pump pulse, as well as equal pump spot sizes. The corresponding onsets of laser-like
emission and slope efficiencies are also investigated.
In this work we present a comprehensive review of recent work carried out by our group in the field of
optical refrigeration of Nd-doped solids. Several infrared thermography measurements in Nd-doped
KPb2Cl5 crystals and micro-powders both above and below the barycentre of the 4F3/2 are presented.
These include some of our most recent ones obtained by employing a novel technique that allows one to
perform differential temperature measurements. The role of both the direct anti-Stokes absorption
processes and those assisted by either excited state absorption or energy transfer upconversion in the
cooling process is discussed.
In this work, we report the upconversion emission from Pr3+ and Nd3+ ions in potassium lead chloride crystal KPb2Cl5after excitation in the 4F5/2,3/2 levels of Nd3+ ions. We have observed violet, blue, green, orange, and red emissions at
room temperature. Blue emission from Pr3+ ions is induced by near infrared laser excitation of Nd3+ through energy
transfer from Nd3+ to Pr3+ ions. The mechanisms leading to the visible emissions have been investigated by studying the
dependence of the upconversion luminescence on the excitation wavelength and intensity of the IR pump light.
In the present work, we report on infrared thermography measurements in Nd-doped KPb2Cl5 crystal and
powder above and below the barycentre of the 4F3/2 level that were performed in order to assess the
relative weights of both the direct anti-Stokes absorption processes and those assisted by either excited
state absorption or energy transfer upconversion when cooling takes place in the material. As the laser
induced temperature changes are usually small, we used a special configuration of the samples that
allowed us to obtain differential measurements where an undoped sample acted as a temperature baseline.
This method allows us to ascertain whether the recorded temperature changes are optically induced or
they are due to some other effect.
We report the first observation of two-photon pumped random laser action in the ground powder of a silica gel
containing rhodamine 6G doped silica nanoparticles. When this solid-state dye system is pumped with 800 nm
femtosecond-lasing pulses, random laser-like effects such as spectral narrowing and temporal shortening are observed
with a laser-like emission peak centered around 598 nm. A comparison between the emission features, random laser
behavior and threshold of random laser action, following one- and two-photon excitations is also performed.
Herein we report efficient random lasing in two powder samples containing rhodamine 6G (Rh6G) doped SiO2
nanoparticles which are either directly dispersed within pure silica particles or embedded in a silica gel matrix which is
subsequently ground. Basic properties of random lasing such as emission kinetics, emission spectrum, and stimulated
emission threshold are investigated in both novel solid-state materials by real-time spectroscopy. The laser-like emission
dynamics of the ground powder obtained out of a bulk silica gel containing 2% Rh6G-SiO2 nanoparticles was accurately
described by a light diffusive propagation model. The device behavior is close to a conventional ultrafast Q-switched
laser, which is a very interesting feature aimed to further applications.
Chaotic dynamics in a self-pulsating laser diode has been shown theoretically to occur by modulation of the laser current. It has been also shown that synchronization of two chaotic self-pulsating lasers can be achieved by small amounts of optical coupling. This result has been obtained with a deterministic model for the laser intensity. We study coherent synchronization of single mode self-pulsating laser diodes by means of a field-equation model that takes into account phase-effects and spontaneous emission noise. It is shown that the size of the coupling required to achieved synchronization is influenced by spontaneous emission noise and by the linewidth enhancement factor. Numerical simulations are then used to identify the optimum regime for efficient synchronization. It is found that good synchronization can be obtained for large values of the bias current, such that the spontaneous emission plays a minor role. The degree of synchronization is studied as a function of the differences between the master and slave laser parameters. Finally, a sinusoidal signal is used to analyze a chaotic communication system based on self-pulsating laser diodes.