Abnormal size-dependent upconversion emissions and multi-color tuning in Er³⁺-doped CaF₂–YbF₃disordered solid-solution nanocrystals

Abstract

A series of Er(3+)-doped (1 - x)CaF(2)-xYbF(3) (0 ≤ x ≤ 0.6) disordered solid-solution nanocrystals with various mean sizes were successfully prepared by a facile solvothermal route. Interestingly, abnormal size-dependent upconversion emissions were demonstrated in these nanocrystals for the first time. With increasing grain size, an obvious enhancement of red to green emission ratio was observed in the Er(3+) (2 mol%): 0.4CaF(2)-0.6YbF(3) nanocrystals, which is the opposite of the routine size-dependent upconversion emission behavior reported previously. Taking Eu(3+) ions as a structural probe, we investigated the influence of a disordered solid-solution structure on Ln(3+) luminescence, and proposed that Ln(3+) clusters formed in the host should play a key role to induce this unusual size-dependent upconversion emission phenomenon. As a consequence, multi-colors such as green, yellow, and red upconversion emissions can be easily realized by appropriately modifying the Yb(3+) content in the Er(3+)-doped (1 - x)CaF(2)-xYbF(3) nanocrystals. The reported results will deepen the understanding of size effects on the lanthanide upconversion in nanocrystals.

Modifying the size and uniformity of upconversion Yb/Er:NaGdF4 nanocrystals through alkaline-earth doping

“…This is readily explained by the greater multi-phonon relaxation probabilities of Er 3+ in smaller NCs having a high surface-to- 35 volume ratio (so that a larger proportion of Er 3+ ions are located on the surfaces and under the influence of high energy vibration groups such as stabilizing ligands, solvent molecules and surface defects). 43 In addition, the experiments taking Eu 3+ as the structural probe, to investigate the modification of symmetry 40 around rare earth ions induced by Ca 2+ doping, were also conducted. As exhibited in Figure S15, the intensity ratio of 5 D 0 → 7 F 2 / 5 D 0 → 7 F 1 increases gradually with increasing of Ca 2+ doping content.…”

Highly Intensified Upconversion Luminescence of Ca2+‐doped Yb/Er:NaGdF4 Nanocrystals Prepared by a Solvothermal Route

“…In this case, the multi-phonon relaxation probability of Ln 3 + activators in the small NCs is high since a large proportion of Ln 3 + ions are located on the surfaces and under the influence of defects and organic groups acting as quenching centers. [26,27] Mean sizes of the xCa/Yb/ Er:NaGdF 4 NCs (x = 0, 10, 20, 30, and 40 mol %) were about 45 nm, 35 nm, 25 nm, 30 nm, and 42 nm, respectively (see the histograms in Figure S10 in the Supporting Information), as determined from TEM images. As all Ca-doped samples are smaller in size than the Ca-free one, the contribution of a size effect to the enhanced UC luminescence for the Ca 2 + -doped samples can be excluded.…”

Transparent organic/inorganic nanocomposites for tunable full-color upconversion

“…As can be seen in Fig. The composition tuning of Er 3+ UC emission has been reported in a variety of hosts in both bulk and nanoscale forms, [30][31][32] while the related detailed mechanisms are still under debate. Incorporation of 1 wt% NCs results in only 5% loss of transmittance and the absorption peaks located in 900 nm and 1016 nm belong to the organic resin matrix.…”

“…3a-c is probably due to clustering of NCs and inhomogeneous distribution of NCs in PDMS. 31,35 Consequently, nanocomposites with arbitrary UC emission color can be fabricated by selecting proper NCs, as demonstrated in Fig. After optimization of the composition, we obtained the white-light emitting transparent composite with ratio of NCs, red: green: blue = 45:1:4.…”