Structural, photoluminescent properties and Judd-Ofelt analysis of Eu3+-activated CaF2 nanocubes

Eu3+-doped CaF2 nanocubes with variable europium concentration, [Eu3+] = 0, 0.6, 1.3, 1.7, 2.2 and 5.4 mol%, have been synthesized by a direct precipitation route. It has been found that, within this concentration range, the nanoparticles present the fluoride-type crystalline structure and the characteristic cubic shape of CaF2 crystals. The nanoparticle size follows a log-normal distribution with a mean value decreasing with the Eu3+ content. Rietveld refinement has been performed to calculate the lattice parameter and crystallite size. Eu3+ concentration affects both parameters giving rise to an increase in the lattice parameter and a reduction of crystallite size. The luminescent properties of Eu3+ ions in these nanostructures have been investigated under CW and pulsed excitation. A Judd-Ofelt analysis, as function of the Eu3+ content, has been performed to determine the transition probabilities, radiative lifetimes and branching ratios of the 5D0 emitting level. It was found that and Judd-Ofelt intensity parameters are dependent on the doping level, showing an evolution that indicates a decrease in the Eu3+ site local symmetry with increasing Eu3+ concentration. Finally, it has been observed that the characteristic luminescence decay time of the 5D0 manifold is reduced with increasing Eu3+ concentration. This effect is partially due to an increase of radiative transition probability, associated with a reduction in the local symmetry of the lanthanide ions, and also to the occurrence of concentration quenching effectsThis work has been partially supported by Ministerio de Economía y Competitividad and Ministerio de Ciencia, Innovación y Universidades under projects MAT2016-75716-2-2-R and RTI2018- 101020-B-I00

Media 1: Temporal dynamics of IR-to-visible up-conversion in LiNbO₃:Er³⁺/Yb³⁺: a path to phosphors with tunable chromaticity

Originally published in Optical Materials Express on 01 November 2012 (ome-2-11-1529

Crystal Structures and Photoluminescence across the La₂Si₂O₇–Ho₂Si₂O₇ System

It is well-known that when an RE₂Si₂O₇ matrix is doped with active lanthanide ions, it displays promising luminescent responses for optical applications. The crystalline structure adopted by the silicate matrix as well as the distribution of the dopants among the available RE crystallographic sites have important effects on the luminescent yields of these compounds. The present study is aimed at analyzing the structural behavior as well as the luminescent properties of Ho³⁺-substituted La₂Si₂O₇. Several compositions across the La₂Si₂O₇–Ho₂Si₂O₇ system were synthesized using the sol–gel method followed by calcination at 1600 °C. The resulting powders were analyzed by means of X-ray and neutron diffraction to determine the phase stabilities across the system. The results indicated a solid solubility region of G-(La,Ho)₂Si₂O₇ which extends to the La_0.6Ho_1.4Si₂O₇ composition. Compositions richer in Ho³⁺ show a two-phase domain (G+δ), while δ-(La,Ho)₂Si₂O₇ is the stable phase for Ho³⁺ contents higher than 90% (La_0.2Ho_1.8Si₂O₇). Anomalous diffraction data interestingly indicated that the La³⁺ for Ho³⁺ substitution mechanism in the G-(La,Ho)₂Si₂O₇ polymorph is not homogeneous, but a preferential occupation of Ho³⁺ for the RE2 site is observed. The Ho³⁺-doped G-La₂Si₂O₇ phosphors exhibited a strong green luminescence after excitation at 446 nm. Lifetime measurements indicated that the optimum phosphor was that with a Ho³⁺ content of 10%

Crystal Structures and Photoluminescence across the La₂Si₂O₇–Ho₂Si₂O₇ System

It is well-known that when an RE₂Si₂O₇ matrix is doped with active lanthanide ions, it displays promising luminescent responses for optical applications. The crystalline structure adopted by the silicate matrix as well as the distribution of the dopants among the available RE crystallographic sites have important effects on the luminescent yields of these compounds. The present study is aimed at analyzing the structural behavior as well as the luminescent properties of Ho³⁺-substituted La₂Si₂O₇. Several compositions across the La₂Si₂O₇–Ho₂Si₂O₇ system were synthesized using the sol–gel method followed by calcination at 1600 °C. The resulting powders were analyzed by means of X-ray and neutron diffraction to determine the phase stabilities across the system. The results indicated a solid solubility region of G-(La,Ho)₂Si₂O₇ which extends to the La_0.6Ho_1.4Si₂O₇ composition. Compositions richer in Ho³⁺ show a two-phase domain (G+δ), while δ-(La,Ho)₂Si₂O₇ is the stable phase for Ho³⁺ contents higher than 90% (La_0.2Ho_1.8Si₂O₇). Anomalous diffraction data interestingly indicated that the La³⁺ for Ho³⁺ substitution mechanism in the G-(La,Ho)₂Si₂O₇ polymorph is not homogeneous, but a preferential occupation of Ho³⁺ for the RE2 site is observed. The Ho³⁺-doped G-La₂Si₂O₇ phosphors exhibited a strong green luminescence after excitation at 446 nm. Lifetime measurements indicated that the optimum phosphor was that with a Ho³⁺ content of 10%