RESUMO
Glass and glass-ceramics containing nanocrystals of Bi2Te4O11 cubic phase co-doped with Er3+ and Yb3+ were prepared by heat treatment of the precursor tellurite glass and investigated for optical applications. Lanthanide doped tellurite glass and glass-ceramics have been extensively investigated because of their optical and photoluminescence performance for technological photonic applications. Er3+ and Er3+/Yb3+ doped TeO2-GeO2-K2O-Bi2O3 tellurite glass compositions were prepared by the conventional melt-quenching method. Photoluminescence results showed the important role played by Yb3+ ions when co-doping with Er3+ ions in comparison with the Er3+ single-doped glass. Due to their larger absorption cross-section, Yb3+ species significantly absorbs 980 nm photons and effectively transfers them to Er3+ ions via a set of mechanisms including ground-state absorption (GSA), excited-state absorption (ESA), and energy transfer upconversion (ETU). Er3+/Yb3+ co-doped sample was chosen for the synthesis of transparent glass-ceramics by controlled heat treatment above Tg for 5 to 120 min. X-ray diffraction patterns, high-resolution transmission electron microscopy (TEM) images, and selected area electron diffraction (SAED) from Er3+/Yb3+ co-doped glass-ceramic samples were used to verify the nanocrystal precipitation, crystalline phase, and chemical nature. The structural change resulting from the crystallization of Bi2Te4O11 nanocrystals was evaluated by the Raman shift of the bands between 300-500 cm-1, which are assigned to the formation of Bi-O-Te linkages and the reduction of [TeO3] depolymerized units. The effects of HT time on the glass-ceramic's optical and upconversion photoluminescence properties were studied in the visible range under excitation at 980 nm in terms of the energy transfer mechanisms from Yb3+ to Er3+. Results indicate that Er3+/Yb3+ co-doped tellurite glass and glass-ceramics are potential candidates for photonic applications in lighting, energy conversion, and luminescent solar cell concentrators.
RESUMO
A new series of dinuclear dysprosium(III) complexes, [Dy2(LCH3)2(NO3)2(MeOH)2] (I), [Dy2(LCH3)2(NO3)2(DMF)2]·2DMF (II), [Dy2(LCl)2(NO3)2(DMF)2]·2DMF (III), and [Dy2(LCH3O)2(NO3)2(DMF)2] (IV), with 2,2'-[[(2-pyridinylmethyl)imino]di(methylene)]bis(4-R-phenol), where R = CH3, Cl, and CH3O, were investigated as potential white light emitters. All octacoordinated dysprosium(III) are phenoxo-bridged species and have a similar coordination environment. Nevertheless, I has a MeOH ligand molecule, while for II-IV a DMF ligand replaces that of MeOH. The nature of the coordinated solvent molecule plays an important role in the behavior of the thermal dependence of the Y/B (yellow/blue) emission ratio of the DyIII complexes (Y: 4F9/2 â 6H13/2, yellow and B: 4F9/2 â 6H15/2, blue transitions),, since for I the variation of this ratio is significant, while for the other DyIII complexes with DMF as ligand the ratio remains constant within experimental error. At room temperature the CIE (Commission International d'Eclairage) color coordinates for the DyIII complexes, I (0.286, 0.317), III (0.302, 0.324), and IV (0.322, 0.348) are close to the NTSC (National Television System(s) Committee) standard value for white color. Varying the temperature from 16 to 300 K the CIE coordinates for I change from the blueish to white region of the chromaticity diagram, while those of II present an inverse thermal dependence as compared to I. The CCT (Correlated Color Temperature) values at room temperature for I (8384 K), II (17235 K), and IV (5948 K) permit us to consider these complexes as candidates for white cold light emitters, the high value of II being uncommon. For I and II the CCT values vary strongly with temperature, showing a decrease with increasing temperature for I, and an increase with increasing temperature for II, thus making evident the influence on the photophysical properties of the nature of the coordinated solvent molecule in these complexes.
RESUMO
We report a novel bright deep-blue-emitting crystal form based on a simple cadmium coordination polymer with an impressive external photoluminescence quantum yield of 75.4(9)%.
