E. Camarillo

Optical Detection of Ion Impurity Sites in Doped LiNbO3

In this work the site location of several M[sup 3+] (m[equals]Cr, Nd, Eu, Ho, Er, Tm) dopant ions in LiNbO[sub 3] has been investigated by using optical (absorption and site-selective fluorescence) techniques. Experimental results reveal that the regular cation sites, Li[sup +] and Nb[sup 5+], are occupied in all cases and can be characterized optically. Additional crystal field sites, for M[equals]Nd and M[equals]Eu, have been detected by site selective spectroscopy. The effects on the M[sup 3+] optical spectra of the stoichiometry and the codoping with MgO have been systematically investigated. The appearance of new sites for the M[sup 3+] ions, M[sup 3+] [minus]Mg[sup 2+], is ascertained for M[equals]Cr, Nd, Ho, Ho, and Tm.

Spectroscopic characterization of Er3+ transitions in Bi4Si3O12

A systematic investigation of optical absorption and luminescence is presented for Er3+ ions in the Bi4Si3O12 crystal. The intrinsic emission of this crystal gives rise to a radiative energy transfer among the host lattice and Er3+ ions. Measured oscillator strengths for seven different transitions from the ground state to excited state manifolds compare favourably with the electric dipole oscillator strengths calculated from the Judd?Ofelt formalism. Radiative lifetimes of the former seven excited states were determined from calculated spontaneous emission probabilities. The ratio of the excited state absorption oscillator strength to the ground state absorption oscillator strength turned out to be similar to those found for materials pumped efficiently at 4I11/2 level excitation wavelengths. The stimulated emission cross section and gain spectra were determined for the transition of special interest for laser application.

Photoluminescent spectroscopy measurements in nanocrystalline praseodymium doped zirconia powders

Praseodymium doped zirconia powder (ZrO2: (0.53 at%) Pr3+) was prepared by a co-precipitation technique and annealed in air at a temperature Ta = 950 °C. The x-ray diffraction pattern shows a nanocrystalline structure composed of 29.6% monoclinic and 70.4% cubic-tetragonal phases. Medium infrared and Raman analysis confirms the monoclinic/cubic-tetragonal crystalline structure and proves the absence of praseodymium aggregates in the material. Photoluminescent spectroscopy over excitations of 457.9 and 514.9 nm (at 20 K), shows two emission spectra composed of many narrow peaks in the visible–near infrared region (VIS-NIR) of the electromagnetic spectrum, associated with 4f inter-level electronic transitions in praseodymium ions incorporated in the zirconia. Excitation and emission spectra show the different mechanisms of the direct and non-direct excitation of the dopant ion (Pr3+), and the preferential relaxation of the material by charge transfer from the host (zirconia) to the 4f5d band and the 4f inter-level of the dopant ion (Pr3+). No evidence of energy transfer from the host to the dopant was observed.

Red and green fluorescence of Mn2+ in NaCl

Abstract The fluorescence (emission and excitation) spectrum of Mn 2+ ion in NaCl has been investigated for freshly quenched samples (diluted Mn 2+ ions) and as grown samples (Mn 2+ ions forming aggregates and/or precipitates). Two main emission bands are generally observed in as grown samples, peaking at 505 nm and around 610 nm. Both emission bands are related to different manganese precipitates. Quenched samples show only the red emission but peaking at 605 nm and with a different excitation spectrum to that of the as grown crystals. Thus, this crystal is suitable to operate as a double color (red and green) emitting phosphor where the red and green relative intensities can be controlled by a thermal treatment.

Gold nanorods for optimized photothermal therapy: the influence of irradiating in the first and second biological windows

The light-to-heat conversion efficiency of gold nanorods (GNRs) with surface plasmon resonances in the first (700–950 nm) and second (1000–1350 nm) biological windows has been studied by Quantum Dot based Fluorescence Nanothermometry. It has been found that red-shifting the GNR longitudinal surface plasmon resonance wavelength (λSPR) from the first to the second biological window is accompanied by a remarkable (close to 40%) reduction in their heating efficiency. Based on numerical simulations, we have concluded that this lower heating efficiency is caused by a reduction in the absorption efficiency (ratio between absorption and extinction cross sections). Thermal stability and ex vivo experiments have corroborated that GNRs with λSPR at around 800 nm seem to be especially suitable for efficient photothermal therapies with minimum collateral effects.

Optical absorption spectroscopy of Nd3+ in the Ca3Ga2Ge3O12 laser garnet crystal

Abstract A systematic investigation of the optical absorption of the Nd 3+ ion in the Ca 3 Ga 2 Ge 3 O 12 :Nd 3+ garnet (CGGG:Nd) crystal is presented. An assignment of the Stark energy levels was carried out assuming a D 2 symmetry site for the Nd 3+ ions in CGGG:Nd. Some relevant spectroscopy parameters for laser applications: radiative lifetime, branching ratios and quantum efficiency from the 4 F 3/2 emitting state were estimated using the Judd–Ofelt theory.

Nd3+ centres induced by ZnO or MgO codoping LiNbO3

Laser spectroscopy has been applied to systematically investigate the effect of MgO or ZnO codoping on the Nd3+ centres formed in LiNbO3. Both codopant oxides produce the same effect, so two new Nd3+ centres appear in both LiNbO3(MgO):Nd and LiNbO3(ZnO):Nd crystals. These new centres correspond to a small percentage (less than 1%) of Nd3+ ions, which are displaced from Li+ sites to a new lattice site. The possible sites for these Nd3+ centres are discussed.

Infrared fluorescence spectra of Nd3+ sites in gadolinium gallium garnet:Nd and gadolinium gallium garnet:Nd,Cr

The fluorescence (excitation and emission) spectra of Nd3+ ions in gadolinium gallium garnet (GGG):Nd and GGG:Nd,Cr have been investigated in the spectral region of laser interest, 4F3/2→4I11/2 transitions. Four sites, denoted as α, β, γ, and δ are present in GGG:Nd, while two additional sites, e and ζ, appear in GGG:Nd,Cr crystals. Site selective excitation (by using a Ti‐sapphire laser) has permitted to obtain the energy level values for each Nd3+ site. This information is necessary for making lasers with these materials. Thus, it has been determined that the γ site is the responsible for laser action in the GGG:Nd minilasers.

Nd3+ active sites in Nd:MgO:LiNbO3 lasers

The fluorescence (excitation and emission) spectra of Nd3+ in Nd:MgO:LiNbO3 have been systematically investigated in order to identify the Nd3+ sites responsible for the two, π (1.085 μm) and σ (1.093 μm), infrared laser lines. Experimental results reveal that Nd3+ ions entering both Li+ and Nb5+ lattice sites are responsible for the π emission line (1.085 μm), whereas Nd3+ ions perturbed by close Mg2+ ions, called Nd‐Mg sites, are the sites producing the σ emission line (1.093 μm).

Basic optical absorption of Er in Bi2TeO5 single crystals

Abstract The basic absorption spectra of Er in Bi 2 TeO 5 crystals are presented and analyzed. Eight transitions were identified from the 4 I 15/2 ground state with all the possible Stark components at 10 K. Further splitting of the lines indicated three major sites for Er 3+ in the crystal. Transitions from the higher Stark levels of the ground state were identified at 200 K. The spectroscopic observations are in good agreement with previous results on oxide crystals exhibiting similar coordination number and symmetry.