Site symmetry and host sensitization-dependence of Eu3+ real time luminescence in tin dioxide nanoparticles.

The present work gives a detailed investigation of the dependence of the real time luminescence of Eu3+-doped tin dioxide nanopowder on rare earth (RE) site symmetry and host defects. Ultrafast time-resolved analysis of both RE-doped and undoped nanocrystal powder emissions, together with electronic paramagnetic resonance studies, show that host-excited RE emission is associated with RE-induced oxygen vacancies produced by the non-isoelectronic RE-tin site substitution that are decoupled from those producing the bandgap excited emission of the SnO2 matrix. A lower limit for the host-RE energy transfer rate and a model for the excitation mechanism are given.

Diffusive random laser modes under a spatiotemporal scope.

At present the prediction and characterization of the emission output of a diffusive random laser remains a challenge, despite the variety of investigated materials and theoretical interpretations given up to now. Here, a new mode selection method, based on spatial filtering and ultrafast detection, which allows to separate individual lasing modes and follow their temporal evolution is presented. In particular, the work explores the random laser behavior of a ground powder of an organic-inorganic hybrid compound based on Rhodamine B incorporated into a di-ureasil host. The experimental approach gives direct access to the mode structure and dynamics, shows clear modal relaxation oscillations, and illustrates the lasing modes stochastic behavior of this diffusive scattering system. The effect of the excitation energy on its modal density is also investigated. Finally, imaging measurements reveal the dominant role of diffusion over amplification processes in this kind of unconventional lasers.

Real time random laser properties of Rhodamine-doped di-ureasil hybrids.

This investigation explores, for the first time, the random laser behavior of ground powder obtained from organic-inorganic hybrid materials based on Rhodamine 6G incorporated into a di-ureasil matrix. The experimental results, both in the spectral and temporal domains, obtained by pumping with picosecond laser pulses, show the existence of efficient random laser emission in this system. Finally, the random laser performance is compared with the one of other Rhodamine-doped solid state silica compounds.

1Low threshold random lasing in dye-doped silica nano powders.

Random laser action is demonstrated in two kinds of 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. Both organic-inorganic hybrid materials present different laser thresholds and emission features which are systematically studied and compared. The dependence of the emission kinetics, emission spectrum, random laser threshold and slope efficiency on the dye doped nanoparticles concentration is investigated in both cases. We also explore if the incorporation of additional TiO2 scatterers could enhance the random laser operation of the studied systems.

Broadband laser tunability of Nd3+ ions in 0.8CaSiO3-0.2Ca3(PO4)2 eutectic glass.

Site-selective spectroscopy and stimulated emission experiments performed in the (4)F(3/2)-->(4)I(11/2) laser transition of Nd(3+)-doped 0.8CaSiO(3-) 0.2Ca(3)(PO(4))(2) eutectic glass are presented. The spectral features of the excitation spectra and those of spontaneous and stimulated emissions reveal the existence of a very complex crystal field site distribution for Nd(3+) ions. As a consequence, the stimulated emission of Nd(3+) in this glass shows a tunability of about 10 nm as a function of excitation wavelength.

Ultrafast random laser emission in a dye-doped silica gel powder.

We report efficient random lasing in a ground powder of a novel solid-state material based on silica gel containing SiO(2) nanoparticles embedding rhodamine 6G (Rh6G) dye. Basic properties of random lasing such as emission kinetics, emission spectrum, and threshold of stimulated emission are investigated by using real-time spectroscopy. The laser-like emission dynamics can be accurately described by a light diffusive propagation model. The device behavior is close to a conventional ultrafast Q-switched laser, which is an interesting fact aimed to further applications.

Spectroscopy and concentration quenching of the infrared emissions in Tm(3+)-doped TeO(2)-TiO(2)-Nb(2)O(5) glass.

In this work, we report the optical properties of Tm(3+) ions in tellurite glasses (TeO(2)-TiO(2)-Nb(2)O(5)) for different Tm(3+) concentrations ranging between 0.05 and 1 wt%. Judd-Ofelt intensity parameters have been determined to calculate the radiative transition probabilities and radiative lifetimes of excited states. The stimulated emission cross-sections of the infrared emissions at 1487 nm and 1800 nm have been determined from the line shape of the emission spectra and the lifetimes of levels (3)H(4) and (3)F(4) respectively. The emission spectra obtained under 793 nm excitation reveal the existence of energy transfer via cross-relaxation among Tm(3+) ions. As a result, the intensity of the infrared (3)H(4)?(3)F(4) emission at 1487 nm decreases in relation to the one at 1800 nm, as concentration increases. The non-exponential character of the decays from the (3)H(4) level with increasing concentration indicates the presence of a dipole-dipole quenching process assisted by energy migration. The self-quenching of the (3)F(4)?(3)H(6) emission at 1800 nm can be attributed to limited diffusion within the active centers.

Random Laser Action in Nd:YAG Crystal Powder.

This work explores the room temperature random stimulated emission at 1.064 µm of a Nd:YAG crystal powder (Neodymium-doped yttrium aluminum garnet) in a very simple pump configuration with no assistance from an internal mirror. The laser threshold energy as a function of pump beam area and pump wavelength has been measured, as well as the temporal dynamics of emission pulses. The absolute energy of stimulated emission and the absolute laser slope efficiency have been measured by using a method proposed by the authors. The results show a surprising high efficiency that takes the low Nd3+ ion concentration of the crystal powder into account.

Influence of Upconversion Processes in the Optically-Induced Inhomogeneous Thermal Behavior of Erbium-Doped Lanthanum Oxysulfide Powders.

The efficient infrared-to-visible upconversion emission present in Er-doped lanthanum oxysulfide crystal powders is used as a fine thermal sensor to determine the influence of upconversion processes on the laser-induced thermal load produced by the pump laser and to assess the potentialities of this material in order to obtain anti-Stokes laser-induced cooling. The analysis of the upconversion emission and excitation spectra as well as the decay curves indicates that energy transfer upconversion is the main mechanism responsible for the green (4S3/2) and red (4F9/2) upconversion luminescence. The dependence on temperature of the intensity ratio of upconversion emission from thermally-coupled ²H11/2 and 4S3/2 levels of Er3+ in the 240-300 K temperature range has been used to estimate a relative sensitivity of 1.09 × 10-2 K-1. Thermal measurements performed on the powder samples by using a thermal infrared camera exhibit a very inhomogeneous heat distribution at the sample surface due to the random distribution of the pumping energy inside the sample as well as to the random properties of the thermal field. The analysis of both spectroscopic and thermal measurements show that after a transient heating induced by the background absorption, cooling of discrete regions by means of anti-Stokes processes can be observed.