M.A. Meneses-Nava

Luminescence and visible upconversion in nanocrystalline ZrO2:Er3+

The structural and luminescence properties of erbium doped zirconium oxide prepared by the sol-gel processes were analyzed. The annealed powders presented a concentration dependent crystallite sizes and crystalline phase, ranging from 28 to 46 nm and from 40 to 96% for the monoclinic phase, respectively. Green (545 nm) and red (680 nm) emissions bands were observed with 489 and 962 nm excitation. Experimental results showed that the emission bands can be tuned by controlling the Er3+ concentration and that the red band is almost quenched with 489 nm whereas it is enhanced with 962 nm excitation. The nature of this behavior is discussed taking into account the nonradiative energy transfer and cross-relaxation process.

Energy back transfer, migration and energy transfer (Yb-to-Er and Er-to-Yb) processes in Yb, Er:YAG

A comparison and discussion of the energy back transfer, migration of energy and direct energy transfer process, from Yb-to-Er and Er-to-Yb ions, in the luminescent system Yb, Er: YAG are presented. The sample crystal was excited with a tunable optical parametric oscillator system. The Yb ions as donors were excited at 940 nm and its fluorescence decay measured at 1030 nm. On the other hand, the Er ions as donors were excited at 800 and 670 nm, and the fluorescence decay of Yb ions as acceptors measured at 1030 nm. The analysis is done through the solution to the General Energy Transfer Master Equations. The ytterbium fluorescence decays in both cases were fitted and found that the migration of the energy among Yb ions is neglected when they act as acceptors.

Effects of energy back transfer on the luminescence of Yb and Er ions in YAG

The back-energy-transfer process from acceptors to donors is included to predict and explain the nonradiative energy-transfer processes among Yb–Er ions in a YAG matrix. This process is in addition to the direct Yb-to-Er energy transfer and the migration of energy among Yb ions. The two measured Yb transients are well fitted by the corresponding solution of the master equations that give the dynamics of the energy-transfer processes.

High diffraction efficiency at low electric field in photorefractive polymers doped with arylimine chromophores

We report on the high photorefractive performance of organic polymers doped with arylimine chromophore (diethylaminosalicylaldiminato)nitrobenzene (H1) and its derivative (diethylaminophenylaldiminato)nitrophenol (H2). Polymer blends of H1 and H2 with PVK : ECZ : C60 at 25 : 49 : 25 : 1 wt% and H2 : PVK : ECZ : PC61BM at the same concentration were fabricated. The electric field (E) steady-state diffraction efficiency dependence and the optical gain were measured through holographic experiments at room temperature. For polymers based on chromophore H2, overmodulation of the diffraction efficiency was measured at just E = 32 V µm−1 obtaining 75%, and for polymers based on H1, diffraction of 87% (overmodulation) at E = 48 V µm−1 was observed. Holographic recording imaging was demonstrated at an electric field of just 10–14 V µm−1.

The red emission in two and three steps up-conversion process in a doped erbium SiO2–TiO2 sol–gel powder

The spectra of the two and three photon up-conversion process in SiO 2 -TiO 2 -doped erbium is studied and the nature of the red emission discussed. In both processes, the red emission ( 4 F 9/2, → 4 I 15/2 ) is measured, however, when pumped directly at 490 nm such emission is not observed. The two-photon up-conversion has to take place first in order to observe the red emission; meanwhile for the case of the three-photon up-conversion it is not necessary for this process to occur first. The fluorescence decay of the green up-converted and direct pumped green emissions were measured and consistently with our results a non-exponential decay is observed.

Optimal co-doping concentrations and dynamics of energy transfer processes for Tm3+-Tb3+ and Tm3+-Eu3+ in LiYF4 crystal hosts

The dynamics of energy transfer processes in Tm+3-Tb+3 and Tm3+-Eu+3 co-doped LiYF4 crystal hosts were studied from time-resolved Tm3+ fluorescence analysis to estimate the optimal co-doping concentrations which maximize 1.5??m laser emission from the 3H4 state of Tm3+. The?analysis was carried out by finding a numerical solution to the general master equations that govern non-radiative energy transfer processes in crystalline materials and by using the Monte Carlo technique. Our analysis improves the description of experimental fluorescence decay curves. The?predicted optimal co-doping concentrations and laser threshold for these luminescent systems are lower than those reported using traditional models for non-radiative energy transfer processes.

Synthesis and nonlinear optical behavior of Ag nanoparticles in PMMA

In this work we have synthesized silver nanoparticles in Poly (methyl methacrylate) (PMMA). This was achieved by polymerizing the mixture of monomer and corresponding metal compound, followed by post-heating treatment. The linear absorption coefficient of the samples was measured using a spectrophotometer, where an absorption peak at 420nm was observed. This peak grows up and shifts as a function of the concentration of the radical initiator. The linear refractive index was measured using the Fresnel equations and agrees with previous reported results. The nonlinear properties were obtained using the single lens Z-scan method, where the nonlinear absorption coefficient (Δα) was found between 5.5975514 and 17.9483493cm-1. The nonlinear refractive index coefficient (Δη) was found to be negative and its value oscillates between 12.9099 E-06 and 22.4276 E-06. Finally, the third-order coefficient (χ(3)) was calculated in the range of 233-787 E-9 esu.

Effect of PMMA impregnation on the fluorescence quantum yield of sol–gel glasses doped with quinine sulfate

Abstract The fluorescence quantum yield of quinine sulfate in sol–gel and PMMA impregnated glasses is measured. The observed quantum yield improvement in the sol–gel matrix, compared to ethanol, is interpreted as a reduction of non-radiative relaxation channels by isolation of the molecules by the cage of the glass. PMMA impregnated sol–gel glasses show an extra improvement of the fluorescence yield, which is interpreted as a reduction of the free space and the rigid fixation of the molecules to the matrix.

Exact solution to the general non-radiative energy transfer master equations in crystalline materials

Abstract The microscopic general non-radiative energy transfer master equations are solved for the case of co-doped crystalline materials. With the calculated exact solution, the macroscopic dopant emissions are obtained. In particular, it is shown that our solution unifies the predictions for the donor emission reported by other models for the cases of direct energy transfer and migration among donors. In particular, we refer to the Forster–Dexter, D.L. Huber, Yokota–Tanimoto, and A.I. Burshtein models. Further, our modeling includes the back-transfer and migration among acceptor processes.

Free volume effects on the fluorescence characteristics of sol–gel glasses doped with quinine sulfate

Abstract The broadening of the absorption and fluorescence spectra and the red shift of the fluorescence maximum of quinine sulfate doped sol–gel glasses, before and after PMMA polymer impregnation, are investigated at different concentrations. The fluorescence decay of the quinine sulfate doped samples does not fit to a single exponential, as it does in ethanol solutions. We found that a double exponential gives a good fit to the obtained results. Introduction of solvent to fill the pores of the matrix does not only have the same effect as the polymer, but also reveals the strong attachment of the molecules to the pore walls and the influence of the interaction with the cage.