Dependence of the up-conversion emission of Li+ co-doped Y2O3:Er3+ films with dopant concentration

Down-/Up-Conversion Emission Enhancement by Li Addition: Improved Crystallization or Local Structure Distortion?

“…The absorption and emission transition probabilities of Ln are governed by site-specific selection rules: for C 2 sites, both magnetic (MD) and electric dipole (ED) transitions are allowed, while for S 6 sites only the magnetic dipole transitions are allowed, leading generally to emissions with order(s) of magnitude less intense than those of C 2 sites . According to the literature, upon Li codoping of Ln–Y 2 O 3 , the small ionic radius of Li (0.76 Å compared to 0.9 Å for Y, in 6-fold coordination) enables facile insertion into Y 2 O 3 lattice, either substitutionally ,,,,, or both substitutionally and interstitially ,,,,,,,− generating strain and charge imbalance. Several scenarios have been advanced to explain the emission enhancement by Li addition: (i) the oxygen vacancies resulted from the charge-compensation can remove the inversion symmetry of S 6 site, and thus the forbidden electric dipole transitions become allowed, leading to an increased number of optically active lattice sites; ,,− , (ii) Li preferentially substitutes for C 2 site, further reducing the local symmetry; (iii) Li addition can reduce the local symmetry at both sites; − ,− ,,,− and (iv) the Ln–Ln interactions get weaker via breaking the Ln–Ln clusters in addition to reduced local symmetry. ,,, …”

“…Due to its facile synthesis in the nanometer regime and favorable physical properties such as a high melting point, phase stability, low phonon energy, and low thermal expansion, Y 2 O 3 represents an excellent host material for the luminescent lanthanide ions. − Li addition to Ln–Y 2 O 3 is considered as an effective optimization strategy that reportedly boosts the emission intensity from a few times up to 2 orders of magnitude, depending on the type of Ln (co)­dopants and concentrations, synthesis methods, Li concentration, and the mode emission excitation (down- or up-conversion). − Despite that almost 100 publications have been published in the last two decades on Ln,Li–Y 2 O 3 , there is still no consensus being reached on the causes of Li-induced emission enhancement. Several causes for emission enhancement are being considered, such as especially the tailoring of crystal-field via lowering of the local symmetry ,,,,,,,, or/and improved crystallization, − ,− ,,, but also changes of morphology, ,, reduction of surface OH defects, − and sensitization via oxygen vacancies induced by charge compensation. ,, The nature of Li precursors as well as the preparation method were found to also play a key role on the final emission properties. , Larger Ln-Y 2 O 3 crystallites are usually obtained upon addition of Li as evidenced by X-ray diffraction (XRD) patterns − ,− …”

Unusually enhancing high-order photon avalanche upconversion of layered BiOCl:Er3+ semiconductor poly-crystals via Li+ ion intercalation doping

“…Fig. 4 gives decay curves of the green ( 4 S 3/2 ) and red ( 4 F 9/2 ) excited states under excitation with 380 nm, being fitted using a single exponential function [28]. It shows that the decay lifetimes of 4 F 9/2 states increase slightly with increasing Li + ions concentrations; whereas that of the 4 S 3/2 state even decrease by doping Li + ions.…”

Luminescent characteristics of Eu2+/Li+ doped (La-Al)2O3 phosphors and PMMA films activated with them

“…Since EDS technique is not capable of measuring the content of Li, the composition has been determined only for the rest of the components, all samples presented a stoichiometry close to (La-Al) 2 O 3 , within the EDS technique precision. The Eu 2+ doped samples present a 0.7 at % content of Eu, which most likely, is incorporated in substitution of La sites because their radii similitude, this amount of Eu 2+ is low in comparison with the starting dopant content in the source material, this behavior is common in synthesis techniques which operate under atmospheric pressure and gas fluxes (as in this case) [21,22] and has been explained for similar materials considering that the host materials have a saturation limit in their capacity of dopants acceptance, and the un-reacted precursors are eliminated through volatile residues that are clear out from the reaction chamber. Figure 2 shows SEM images for undoped, europium and europium/lithium doped phosphors, these phosphors were mechanically grinded before the annealing processes, therefore they present particles with sharp edges characteristic of this type of grinding process.…”