L. A. O. Nunes

Intermolecular energy transfer and photostability of luminescence-tuneable multicolour PMMA films doped with lanthanide–β-diketonate complexes

It is reported in this work the preparation, characterisation and photoluminescence study of poly(methylmethacrylate) (PMMA) thin films co-doped with [Eu(tta)3(H2O)2] and [Tb(acac)3(H2O)3] complexes. Both the composition and excitation wavelength may be tailored to fine-tune the emission properties of these Ln3+–β-diketonate doped polymer films, exhibiting green and red primary colours, as well as intermediate colours. In addition to the ligand–Ln3+ intramolecular energy transfer, it is observed an unprecedented intermolecular energy transfer process from the 5D4 emitting level of the Tb3+ ion to the excited triplet state T1 of the tta ligand coordinated to the Eu3+ ion. The PMMA polymer matrix acts as a co-sensitizer and enhances the overall luminescence intensity of the polymer films. Furthermore, it provides considerable UV protection for the luminescent species and improves the photostability of the doped system.

Spectroscopy of Nd3+ and Yb3+ codoped fluoroindogallate glasses

The Nd–Nd and Nd–Yb energy transfer processes are studied in lead fluoroindogallate glasses with the following molar composition: 30PbF2–20GaF3–15InF3–15ZnF2–(20–X)CaF2–XNdF3 (with X=0.1, 0.5, 1, 2, 4, and 5), 30PbF2–20GaF3–15InF3–15ZnF2–(20–X)CaF2–XYbF3 (with X=0.1, 0.5, 1, 2, 3, and 5), and 30PbF2–20GaF3–15InF3–15ZnF2–(19–X)CaF2–XYbF3–1NdF3 (with X=0.1, 0.5, 1, 2, 3, and 5.5). The Dexter, Yokota–Tanimoto, and Holstein formalisms were used to treat the experimental data. The following microparameters of energy transfer were obtained: CDD(Nd–Nd)≈7×10−40, CDA(Nd–Nd)=2.5×10−40, and CDA(Nd–Yb)≈3×10−40 cm6/s. It was also shown that the energy migration between Nd ions depends on the third power of temperature (T3) up to a saturation value of about 80 K. This behavior was attributed to the site to site energy migration. The Yb doped samples presented no nonradiative losses for the Yb3+ emission at 969 nm.

On the observation of 2.8 μm emission from diode-pumped Er3+- and Yb3+-doped low silica calcium aluminate glasses

In this letter, we investigate the midinfrared photoluminescence of a series of diode-pumped Er3+-doped and Er3+, Yb3+-codoped low-silica content aluminosilicate glasses. Emission at 2.8 μm was observed in both single doped and codoped samples. The effect of Yb3+ codoping of the Er3+-doped samples was such that, for example, for a 2 wt % Er3+-doped, the photoluminescence yield at 2.8 μm was found to be roughly three times larger than that of the single 2 wt % Er3+-doped sample. This behavior was attributed to the efficient sensitization of Er3+ by Yb3+ in our oxide based host glasses. The results reported in this letter, together with the outstanding mechanical, chemical, and thermal properties of these glasses, suggest that rare-earth doped calcium aluminate glasses may become an attractive host for the development of solid state lasers operating in the midinfrared.

Er3+:Yb3+ codoped lead fluoroindogallate glasses for mid infrared and upconversion applications

In this work, two sets of lead fluoroindogallate glasses were studied with the aim of using them as active media for laser devices at the mid infrared (∼2.8 μm) and visible (∼0.54 μm) regions. The infrared and upconverted emissions of Er3+ in single and Er3+:Yb3+ codoped samples were analyzed, and it was observed that the best set of samples for 2.8 μm emission was the single doped one, and that as the upconversion (anti-Stokes luminescence) increased as a function of Yb3+ concentration, the infrared emission decreased in the same manner. The results suggest that the codoping with Yb3+ favors only the upconversion processes which depopulate the 4I11/2 level, reducing the 2.8 μm emission intensity. On the other hand, the Yb3+ codoping will certainly increase the efficiency of an upconversion based device. Quantum efficiencies of infrared emissions and radiative lifetimes were calculated by using the Judd–Ofelt approximation. Er3+–Er3+ and Er3+–Yb3+ energy transfer efficiencies were calculated using the mea...

Structural and spectroscopic properties of rare-earth (Nd3+,Er3+, and Yb3+) doped transparent lead lanthanum zirconate titanate ceramics

This work presents the structural and spectroscopic characterization of transparent lead lanthanum zirconate titanate ceramics doped with Nd3+, Er3+, or Yb3+ ions. High optical quality samples presenting the perovskite structure were prepared through a mixed oxides method followed by conventional sintering or uniaxial hot pressing. Absorption and luminescence spectra were measured, and radiative emission parameters were calculated for Nd3+- and Er3+-doped samples. The results indicate the potential of these polycrystalline host–ion combinations for the construction of diode-pumped lasers in the near-infrared region.

Localized surface plasmon resonance interaction with Er3+-doped tellurite glass

We show the annealing effect on silver and Erbium-doped tellurite glasses in the formation of nanoparticles (NPs) of silver, produced by the reduction of silver (Ag+ → Ag0), aiming to an fluorescence enhancement. The absorption spectra show typical Localized Surface Plasmon Resonance (LSPR) band of Ag0 NP in addition to the distinctive absorption peaks of Er3+ ions. Both observations demonstrate that the photoluminescence enhancement is due to the coupling of dipoles formed by NPs with the Er3+ 4I(13/2) → 4I(15/2) transition. This plasmon energy transfer to the Er3+ ions was observed in the fluorescence spectrum with a blue-shift of the peaks.

2.8 and 1.55μm emission from diode-pumped Er3+-doped and Yb3+ co-doped lead lanthanum zirconate titanate transparent ferroelectric ceramic

This work reports the observation of intense emissions at 2.8 and 1.55μm from optical quality diode-pumped Er3+-doped lead lanthanum zirconate titanate (PLZT) transparent ferroelectric ceramic. Radiative properties were calculated using the Judd Ofelt theory, and the respective values of η=0.09 and η=0.94 were obtained. The effect of ytterbium co-doping the PLZT: Er3+ samples was investigated in an attempt to increase intensities. It was found that Yb3+→Er3+ energy transfer processes, that favor Er3+ upconversion, are detrimental to the efficiency of midinfrared emissions. Even so, the advantageous spectroscopic characteristics of PLZT: Er3+ associated with its excellent thermal and mechanical properties, indicate it is a potential cost-effective laser active media.

Properties of glasses from fluoride to phosphate composition

Abstract A set of glasses with compositions Pb0.3Ga0.2In0.15Zn0.15Ca0.2F2.35(1−x)(PO3)2.35x (x: 0, 0.1, 0.25, 0.5, 0.75, 0.9 and 1) was prepared to study the change of the physical and structural properties of glasses ranging from fluoride to a metaphosphate glass. The fluoride-based and the phosphate-based glasses were prepared by using fluoride compounds and oxides, carbonates, and NH4H2PO4 as the phosphates components. The fluorophosphate glasses were obtained by melting a proportionate mixture of the two basic compositions. Density, d, refractive index, nd, optical transparency window, characteristic temperatures such as glass transition (Tg) and onset of crystallisation (Tx), were measured as a function of composition. The Pb0.3Ga0.2In0.15Zn0.15Ca0.2F2.35 glass had a glass transition temperature of 265°C, nd=1.564, d=5.64 g cm −3 whereas the Pb0.3Ga0.2In0.15Zn0.15Ca0.2(PO3)2.35 glass had Tg=500° C, nd=1.594, d=3.44 g cm −3 . Structural changes of the glasses as a function of PO3/F ratio, was determined from the infrared and Raman spectra of the samples.

Spectroscopic properties of water free Nd2O3-doped low silica calcium aluminosilicate glasses

Abstract In this work, low silica calcium aluminosilicate glasses (LSCA) doped with different concentrations of Nd 2 O 3 were prepared under vacuum conditions and investigated through spectroscopic measurements. UV, visible and near IR optical absorption spectra, IR luminescence spectra, and fluorescent time decay were measured. Judd–Ofelt model was used in conjunction with these data to calculate intensity parameters (Ω 2 ,Ω 4 and Ω 6 ), emission cross-section, radiative lifetime, branching ratio and fluorescence quantum efficiency. The up-conversion properties of Nd 3+ were investigated following ( 4 G 5/2 + 2 G 7/2 ) excitation, and both visible and UV up-conversion have been observed. These results combined with its high fluorescence quantum efficiency and excellent mechanical properties, suggest that this glass may be a candidate to be used as laser host material for near IR with a further possibility of application in the UV and visible spectral regions.

Cooperative luminescence in Yb3+-doped phosphate glasses

In this paper we present results on cooperative luminescence performed on Yb3+-doped metaphosphate glasses under 980 nm excitation. We have measured emission spectra and decay lifetimes in the visible and infrared regions as a function of Yb concentration. It was observed that, up to 10% of Yb concentration, cooperative emission increases while lifetime is observed to decrease. Such behaviour is attributed to the Yb interaction with OH− radicals and energy migration among Yb ions.