Temperature dependence and temporal dynamics of Mn2+ upconversion luminescence sensitized by Yb3+ in codoped LaMgAl11O19

A detailed spectroscopic study of the upconversion properties in Mn2+-Yb3+ codoped LaMgAl11O19 is presented. Pulsed and continuous-wave infrared excitation in the 2F7/2--2F5/2 Yb3+ absorption peaks induces broad Mn2+ green emission at 19450 cm-1, which is assigned to the 4T1--6A1 transition in tetrahedral Mn2+ and sharp peaks associated with Yb3+-pairs luminescence. Both emissions have very different temporal evolution and can be separated by time-resolved spectroscopy. Among the different concentrations under investigation, the 2%Mn2+-5%Yb3+ codoped system presents the highest upconversion efficiency. The corresponding emission remains visible to the naked eye up to 650 K. The time dependence of the Mn2+ luminescence upon Yb3+ excitation shows distinct behaviors for different doping concentrations. The temporal evolution of the intensity for the diluted system doped with 2%Mn2+ and 5%Yb3+ together with the pure manganese compound doped with 1%Yb3+, as well as the temperature dependence of the upconversion emission intensity and lifetime are relevant to identify the underlying upconversion mechanisms. We show that the main processes responsible for upconversion in this doubly transition-metal rare-earth doped oxide are both ground-state absorption (GSA)/excited-state absorption and GSA/energy-transfer upconversion. An analysis of these processes yielding highly efficient luminescence is discussed on the basis of crystal structure and dopants.This work was financially supported by the Spanish Ministerio de Ciencia e Innovación (Project No. MAT2008- 06873-C02-01/MAT) and the MALTA-Consolider Ingenio 2010 (Reference No. CSD2007-00045). R.M.-R. thanks the Spanish MEC for a FPI research grant (Reference No. BES-2006-13359)

Lighthouse: A spacebased mission concept for the surveillance of geosynchronous space debris from low earth orbit

In this paper, a new mission is proposed for space debris surveillance in geosynchronous orbit (GEO). The mission "Lighthouse", here proposed as a concept study, describes the use of a small satellite in a low polar orbit, equipped with a Schmidt telescope, constantly observing a belt across the geostationary orbit. In this way, a single instrument can sweep the whole orbit everyday regardless the light and weather conditions. Most of observations are nowadays performed by ground telescopes, which are affected by weather conditions and night time duration. Moreover, a single telescope can observe only a portion of the geostationary orbit. The mission concept arose as space application of an ESA ITI (Innovation Triangle Initiative) project designing a Schmidt telescope purposely conceived for the monitoring of NEO (Near Earth Objects) and space debris. A compact version of the telescope (50 cm diameter and 1.61 m length), particularly suitable for space applications, has been designed too. The size and the mass of the telescope enable the use of a small satellite platform, with the related advantages in term of costs and performance. Lighthouse is proposed as a new asset for Space Surveillance and Tracking sensors, complementary to the ground telescopes network

Spectroscopic studies of emission and absorption properties of 38PbO-62SiO(2):Nd3+ glass

The main spectroscopic parameters (intensity parameters, radiative life times, branching ratios, quantum efficiency and emission cross-section of the F-4(3/2)-> I-4(9/2) transition) of the 38PbO-62SiO(2) glass doped with Nd3+ are evaluated using the standard Judd-Ofelt theory. Remarkably low values of the intensity parameters Omega(2,4,6) are explained by structural modifications of the Nd3+ surroundings caused by presence of the Pb ions

Luminescence of Tb-based materials doped with Eu3+: case studies for energy transfer processes

This review addresses the energy transfer processes involving lanthanide ions, analysing in particular the case of the Tb3+\u2192Eu3+ energy transfer processes in terbium-based materials containing Eu3+ as a dopant. These examples are used as case studies for the processes and mechanisms concerning energy transfer generally involving Ln3+ ions, pointing out the differences caused by the structural characteristics of the host. The review introduces the theoretical background of the energy transfer processes, providing a brief description of the possible regimes for the donor-acceptor transfer depending on the donor concentration, together with the general considerations on the specific case of Tb3+\u2192Eu3+ transfer. The review is completed by a brief survey of the literature published on this topic from the 60s to date, including some of the most recent papers

Optical spectroscopy of zinc metaphosphate glasses activated by Ce3+ and Tb3+ ions

The photoluminescence of Ce3+ and Tb3+ ions in zinc metaphosphate glasses is investigated. The blue and green emissions of Tb3+ ions are enhanced upon UV excitation through energy transfer from Ce3+ to Tb3+ ions. The efficiency of such an energy transfer was estimated based on spectroscopic data and resulted in being about 20-23%. Spectroscopic data revealed that the energy transfer occurs via a non-radiative process inside Ce3+-Tb3+ clusters formed in the glass. This ion clustering could be useful for the design of efficient conversion phosphors of ultraviolet to blue and green light

The paramagnetic metal effect on the luminescence of rare-earth-metal complexes with pyridine-based nitrogen ligands

The synthesis and the characterization in the solid state are presented of La(III), Gd(III) and Lu(III) nitrate complexes with the pyridine-based ligands L1 (N,N′-bis(2-pyridylmethylidene)-1,2-(R,R+S,S)-cyclohexanediamine) and L2 (N,N′-bis(2-pyridylmethyl)-1,2-(R,R+S,S)-cyclohexanediamine). The crucial role of the nature of both the lanthanide ion and the ligand in the luminescence spectroscopy of the metal complexes, in the solid state at room temperature, is demonstrated and discussed. In particular, the "paramagnetic effect" of the Gd(III) ion inducing an increased phosphorescence emission is observed in the complex with L1 ligand and, in a lesser extent, in the complex with L2 ligand. At variance with this observation, only fluorescence emission of the La(III) and Lu(III) diamagnetic metal complexes is detected. © 2015 Elsevier B.V. All rights reserved

Spectroscopic investigations of nanostructured LiNbO3 doped with Eu3+

Structural and optical properties of the sol-gel derived nanocrystalline lithium niobate (LiNbO3) powders doped with Eu3+ ions have been studied. In particular, the influence of the sizes of nanoparticles controlled by temperature on the structural and luminescence properties has been investigated. Emission bands corresponding to 5D0 emission became more resolved with increasing nanocrystal size and changed to a typical Eu3+:LiNbO3 single crystal spectrum for nanocrystals having an average size of more than 40 nm. Nonlinear optical properties of nanostructured LiNbO3 have been confirmed by simple observation of second harmonic generation effect (SHG). The possibility of using nanostructured LiNbO3 doped with rare-earth ions as self-doubling elements in integrated optoelectronic devices has been discussed

Synchrotron Radiation Study of Interconfigurational 5d-4f Luminescence of Pr3+ in KLuP2O7

The double phosphate KLuP2O7 doped with Pr3+ ions was prepared by solid-state reaction. The material obtained was characterized by powder X-ray diffraction. The luminescence spectroscopy and the excited state dynamics of this material were studied upon excitation with VUV synchrotron radiation. The 5d-4f emission of Pr3+ upon both direct and band gap excitation was detected and assigned. The decay kinetics of the Pr3+ 5d-4f emission is characterized by a decay time of about 20 ns and is nearly temperature independent within the range 8-300 K. Both dynamics and energy transfer peculiarities revealed in the study suggested good potentials for application of KLuP2O7:Pr3+ as a fast scintillator material