Petrus A. Santa-Cruz

Spectroscopic properties and design of highly luminescent lanthanide coordination complexes

Abstract In this paper recent advances in the development of efficient light conversion molecular devices (LCMD) based on lanthanide complexes are reviewed, with emphasis on the work of our group. We have adopted a strategy based upon both theoretical and experimental (synthesis and methodological) investigations. The theoretical aspects are described in terms of the well known theory of 4f–4f transitions and a recently developed model of intramolecular energy transfer processes in lanthanide coordination compounds. The necessary structural data (coordination geometries and electronic structures of the organic parts of the compounds) are obtained from a sparkle model also recently developed. The results lead us to achieve a better understanding of the factors determining the quantum yields and other relevant properties of these complexes, establishing the basis of a framework for the modeling of new complexes which are promising LCMDs. In addition, the fluorinated compounds, which are sufficiently volatile and thermodynamically stable, are candidates for a number of applications. We illustrate their use as LCMDs devices for sensing UV radiation (dosimeter) and as antireflection coatings (ARC) on silicon solar cells with beneficial effects on device performance.

Compositional dependence of up-conversion process in Tm3+–Yb3+ codoped oxyfluoride glasses and glass-ceramics

Up-conversion of infrared radiation to the visible and ultraviolet regions in PbF2–GeO2–Al2O3–Tm2O3–Yb2O3 oxyfluoride glasses and glass ceramics was obtained, exciting at 1.0 μm with a diode laser at room temperature. Transparent films and microspheres were prepared by a modified spin-coating technique. The effect of host composition on the up-conversion luminescence was studied in order to improve the ultraviolet radiation generation. In the glass samples, the Tm3+ blue (4786 A) and red (6500 A) visible emissions got more intense as the PbF2 content was increased. The main Tm3+ blue emission (4786 A, 1G4→3H6), results from a three-photon process. A second blue emission (4500 A, 1D2→3F4), followed by a UV emission (3650 and 3850 A, 1D2→3H6) was observed in the (2PbF2/GeO2) glass ceramics, in a narrow range of Al2O3 concentration. The 1D2 level of the Tm3+ ions is populated by a fourth photon from the cross-relaxation process given by (3F4,1G4)→(3H6,1D2).

White light simulation by up-conversion in fluoride glass host

Abstract We have produced white light using infrared excitation by addictive synthesis of red, green and blue (RGB) upconverted radiation, in a lanthanide-doped fluoride-based glass, named full-color glass, FCG-III. This glass generates simultaneously RGB emissions from 980 nm excitation by up-conversion process, with high precision of color coordinates and high efficiency. The ions Er 3+ and Tm 3+ were used as simultaneous narrow line emitters of the three primary light colors. The Tm 3+ and Er 3+ concentrations in the glass host were adjusted, favoring light color tuning and generation of a wide color gamut in the visible spectrum, and white light simulation under single infrared excitation.

Red, green and blue light generation in fluoride glasses controlled by double excitation

A new multi-doped fluoroaluminate-based glass was developed to generate, with high accuracy, the three primary light colors 31 31 simultaneously, allowing additive synthesis of light in the visible spectrum. The ions Er and Tm were used as red, green and blue 31 31 narrow line emitters, by down-conversion and up-conversion processes. The Tm and Er concentrations in the glass were defined for simulation of the white emission, under double excitation in the infrared and ultraviolet region, allowing color tuning.

Lanthanide complexes dispersed in enamel: a promising new material for photonic devices

Abstract A lanthanide-thin-film based dosimeter with high sensitivity and selectivity to UV cumulative measurements was developed. The dosimeter is based on nitrocellulose–enamel and has been designed in order to present useful responses covering the three main UV regions related to skin damage effects: UV-A (365 nm), UV-B (315 nm), UV-C (290 nm).The active part of the system is a thin layer of commercial nitrocellulose enamel ultrasound-mixed with lanthanide complex powder. We have monitored the Eu (III) emission ( 5 D 0 → 7 F 2 ) and the Tb (III) emission ( 5 D 4 → 7 F 5 ) as a function of UV exposure time and a luminescence decrease of the Eu (III) emission was observed. Since this effect is irreversible, a memory effect is associated to the system allowing dosimetry measurements. For the red (600 nm), green (540 nm) and blue (430 nm) excitation the luminescence remained the same, which reinforces the UV selectivity of the dosimeter proposed. We may also adjust the dosimeter sensitivity by controlling the amount of powder mixed with the enamel.

Molecular UV dosimeters of lanthanide complex thin films: AFM as a function of ultraviolet exposure

Abstract In a previous work we developed a molecular dosimeter of high sensitivity and selectivity to UV cumulative measurements, using as the active part a thin film produced by thermal evaporation of europium complexes. The Eu 3+ emission ( 5 D 0 → 7 F 2 ) is monitored as a function of UV dose, and a memory effect allows dosimetry measurements. All measurements were quantified by an integration sphere coupled to a radiometer that provides absolute dose measurements in J/cm 2 and may be related to the MED (minimum erythemal dose) of 28 mJ/cm 2 as a reference. In this work, the preliminary results about the photodegradation mechanism of the complexes at molecular level is presented through AFM images. We have observed that the organic ligands, which absorb the UV radiation and transfer to the ion emitters, may be photofragmenting and therefore interfering in the luminescence emission of these ions. This ligand photofragmentation process justifies the selectivity presented by the dosimeter. On the other hand, the non-dependence of the film morphology as a function of UV radiation exposure indicates a different behavior from that which we had suspected before, indicating a non-ablative process, which is the contrary to what was previously suggested.

Kinetic study of the thermal decomposition of Eu3+ with β-diketone ligands and 1,10-phenanthroline or 2,2-dipyridine

Abstract The complexes of general formula: Eu(β-dik) 3 L (where β-dik=4,4,4-trifluoro-1-phenyl-1,3-butanedione (btfa), 4,4,4-trifluoro-butyryl-(+)camphor (hfc) or 2,2-dimethyl-6,6,7,7,8,8-heptafluoro-3,5-octadione (fod) and L=1,10-phenanthroline or 2,2-bipyridine) were synthesized by reacting the corresponding metal salt of chloride with the β-diketone and the other ligands. The thermal decomposition was studied by non-isothermal thermogravimetry. The kinetic models that better described the thermal decomposition reaction for the Eu(β-dik) 3 L, were F1, R1 and R2.

Full-color simulation in a multi-doped glass and controlled quenching of luminescence using Er (III) as a suppressor for a tunable device

Abstract We have developed a multi-doped glassy material (CaF2-B2O3-Sb2O3) to generate and control the primary light colors, allowing the simulation of any color of light by additive synthesis. Tm(III), Tb(III) and Eu(III) ions were used (0.01–5.0 mol%) as blue, green and red narrow line emitters. A wide color gamut was obtained under ultraviolet excitation by changing the material composition. The chromaticity diagram is covered, including the white simulation. We have proposed a mechanism to control the chromaticity of a fixed composition of the material, using the Er(III) ion (0.05–3.0 mol%) as a quencher which may be deactivated by infrared excitation. The first results using Er(III) in our white emitter glass are presented.

Geração e controle das cores luz primárias em vidros para dispositivos "full color"

We are working in a new multi-doped glassy material to generate simultaneously the three primary light color (by addition) of the visible spectrum, with the control of the intensity of each one, allowing the simulation of any color: a full-color generator device. Tm+3, Tb+3 and Eu+3 ions were used (0.01 to 5,0 mol%) as blue, green and red narrow line emitters. A wide color gamut was obtained under ultraviolet excitation by varying the material composition. The chromaticity diagram is covered, including the white simulation.

Lead–germanate glasses: an easy growth process for silver nanoparticles and their promising applications in photonics and catalysis

In this study, we report non-conventional silver nanoparticle growth on the surface of lead–germanate oxide glasses. Thermal annealing at around the glass transition temperature (Tg) under a nitrogen atmosphere enables the growth of silver thin films on the glass surface. The nanoparticle growth was monitored by scanning electron microscopy (SEM) and UV-visible spectroscopy as a function of the annealing time. The characteristic temperatures were obtained by differential thermal analysis (DTA) and the influence of the Ag+ ion content on the glass stability (GS) parameters was evaluated. Additionally, the apparent activation energy of crystallization (E) was calculated. The silver thin films obtained after different annealing times were applied as a substrate for luminescence enhancement of the Eu(btfa)3·bipy rare earth europium complex. The catalytic activity of the Ag-doped glasses was tested for the reduction of p-nitrophenol in the presence of NaBH4. The catalytic performance of the unannealed glass demonstrated an unexpected good efficiency compared with the annealed glass samples.