Controlled morphology and EDTA-induced pure green upconversion luminescence of Er³⁺/Ho³⁺-Yb³⁺ co-doped NaCe(MoO₄)₂ phosphor

Abstract

Uniform and well-crystallized NaCe(MoO 4 ) 2 : Er 3+ /Ho 3+ , Yb 3+ up-conversion (UC) phosphors have been successfully synthesized by a facile hydrothermal route at 180 o C for 12 h at pH=9. The crystalline phase, size and morphology were systematically characterized using powder X-ray diffraction (XRD) and field emission-scanning electron microscopy (FE-SEM). The experimental results showed that the ethylene diamine tetraacetic acid (EDTA) was a key parameter which not only determined their spacial arrangement, but also affected the size distributions of the final products.Moreover, we found that EDTA could tune the band edge absorption of molybdate system by changing the lattice parameters, so as to realize their bicolour tunable luminescence of Er 3+ /Ho 3+ -Yb 3+ co-doped NaCe(MoO 4 ) 2 for the first time. Studies of the behavior as a function of dopant concentration were all described. The different UC mechanism of the samples with and without EDTA were systematically depicted as well. It was found that an innovative route to increase the green UC emission and simultaneously suppress red UC emission in Er 3+ /Ho 3+ -Yb 3+ co-doped NaCe(MoO 4 ) 2 prepared with the assistance of 0.1 g EDTA, which enhanced the efficiency of the single green color.Since the UC luminescence of rare-earth (RE) ions was discovered by Auzel in the mid-1960s, 1-2 it has been the focus of much research. Potential applications include solar cells, 3-6 novel display technologies, 7-9 inks for secure printing 10 and, more recently, biophysics. 11-13 Their advantages include near-infrared (NIR) excitation, low cytotoxicity, weak autofluorescence, high chemical stability, and low photobleaching, which make them more desirable than conventional organic dyes or quantum dots for bioimaging application. 14-17 The photoluminescence emission from rare earth doped materials arises due to the transitions within the 4f n energy manifolds which are forbidden because of the electric dipole selection rule but these are allowed due to the mixing of configurations having opposite parity. One of the most exciting properties of these materials is frequency UC where two or more photons having relatively low energy are absorbed by the material and subsequently converted to a higher energy photon (this is an anti-Stokes process). However, the commonly investigated lanthanide activators such as Er 3+ and Ho 3+ ions contain abundant metastable excited states, and the dominant emission usually lies in the non-green region with relatively low green emission intensity. Hence, a strategy to boost the green emission intensity will be useful for UC applications.It is well known that lattice parameter is the fundamental factor that affects the luminescence property. [18][19] During the hydrothermal process, the introduction of EDTA with functional groups into the reaction system can effectively change the band edge absorption of MoO 4 2of the final product by changing the lattice parameters, which makes effort to build energy level match conditions between relati...

Hierarchical design and control of NaCe(WO4)2crystals: structural and optical properties

“…Tungstate-based scheelites exhibit optical properties of interest for various technological applications. 17,26,82 In the context of future applications based on photocatalysis and photoluminescence, it is necessary to determine the optical bandgaps of the different materials. Furthermore, since the local crystal structure, morphology and micro-particle sizes of NaCeIJWO 4 ) 2 are modified by changing the pH and ligand concentration, 83 we would also expect correlated modifications in the UV-Vis diffuse reflectance spectra of the samples.…”

“…Functional inorganic materials of rare earth (RE) tungstates have attracted extensive attention because of their potential technological applications as catalysts, 13 highperformance phosphors, 14 negative thermal expansion materials, 15,16 and up-conversion materials, 17 which result from the specific 4f shell energy levels of their ions and the empty 5d orbital. 18,19 These RE tungstates are the subject of many studies because of their extraordinary potential in lasers and optical transmission devices e.g., in fiber optics, bio-imaging probes, 20 n-UV chip-based LED lighting 21 and scintillators.…”

Er3+/Yb3+-Codoped ZrO2 Nanocrystals as Ratiometric Luminescence Nanothermometers that Cover Three Biological Windows

“…As known, the UC emission intensity (I) depends on the excitation power (P) following the relation I ∝ P n . 34 Parameter n stands for the number of pump photons which participate in the Er 3+ ion excitation process from the ground state to the emitting one. Figure 4b shows the excitation power dependence of the three UC emission bands in the log−log plots.…”

Sr1/2Ce5/14□1/7WO4: a new modulated ternary scheelite compound

“…The calculated molecular orbital diagram shows that the electron density consists on the O2p atomic orbital for the HOMO and the Ce 4f orbitals for the LUMO, with a band gap of 3.28 eV. Variations of the gap values can be linked to different factors such as shape and crystallite size (Alivisatos, 1996), lattice parameters (Yang et al, 2015) and degree of structural disorder in the lattice (Rosa et al, 2008;Lacomba-Perales et al, 2008). For SrWO 4 , the band gap value shows that the maximum of the valence band can be mainly attributed to O2p levels, whereas the bottom of the conduction band is mainly composed of W 5d levels.…”