Upconversion luminescence properties of BaMoO4: Yb3+, Ln3+ (Ln3+ = Er3+/Tm3+, Er3+/Tm3+/Ho3+) micro-octahedrons

Yb³⁺, Ln³⁺ (Ln³⁺ = Er³⁺/Tm³⁺, Er³⁺/Tm³⁺/Ho³⁺) doped BaMoO₄ micro-octahedrons were synthesized by a hydrothermal process. The as-prepared phosphors were characterized by x-ray powder diffraction, field emission scanning electron microscopy, elemental mapping, energy-dispersive x-ray spectroscopy, x-ray photoelectron spectroscopy, and UV-vis diffuse reflectance spectroscopy. The upconversion luminescence properties of the samples were investigated under 980 nm near infrared excitation. The different concentrations of Er³⁺, Tm³⁺, and Ho³⁺ were used for tuning the multicolor (blue, green, and red) emissions. The multicolor emissions were investigated by Commission Internationale de l'Elcairage chromaticity and decay lifetime. The photon process as well as the energy transfer mechanism between the Yb³⁺ to Er³⁺, Tm³⁺, and Ho³⁺ were described.

Mutual energy transfer luminescent properties in novel CsGd(MoO4)2:Yb3+,Er3+/Ho3+ phosphors for solid-state lighting and solar cells

In this work, we prepared a novel kind of Yb3+,Er3+/Ho3+ co-doped CsGd(MoO4)2 phosphors with a different structure from the reported ALn(MoO4)2 (A = Li, Na or K; Ln = La, Gd or Y) compounds using a high-temperature solid-state reaction method. X-ray diffraction showed that the as-prepared samples had a pure phase. Based on the efficient energy transfer from Yb3+ to Er3+/Ho3+, the up-conversion (UC) luminescence of the optimal CsGd(MoO4)2:0.30Yb3+,0.02Er3+ sample showed intensely green light with dominant emission peaks at 528 and 550 nm corresponding to Er3+ transitions 2H11/2 → 4I15/2 and 4S3/2 → 4I15/2, respectively, as well as a weak emission peak originating from 4F9/2 → 4I15/2 at 671 nm, under 975 nm laser excitation. The CsGd(MoO4)2:Yb3+,Ho3+ samples mainly displayed two emission bands around 540 and 660 nm together with a negligible one at 755 nm, which corresponded to Ho3+ transitions 4F4,5F2 → 5I8, 5F5 → 5I8 and 4F4,5F2 → 5I7, respectively, under 975 nm laser excitation. With increasing Yb3+ concentration in CsGd(MoO4)2:Yb3+,Ho3+ phosphors, the emission color could be tuned from orange red to light yellow due to the large energy gap between levels 4F4,5F2 and 5F5. In addition, the CsGd(MoO4)2:Yb3+,Er3+ showed green light under 376 nm UV irradiation similar to that upon 975 nm laser excitation. However, the emissions for CsGd(MoO4)2:Yb3+,Ho3+ samples under 358 nm UV or 449 nm blue excitation showed dominant emission peaks at 540 nm and weak 660 nm and 752 nm peaks, which were a bit different from those under 975 nm excitation. Interestingly, we observed efficient energy transfer phenomena (possible quantum cutting) from Er3+/Ho3+ to Yb3+ and a Yb3+-O2- charge transfer (CT) transition in the molybdates, which was deduced from the visible and near-infrared emission spectra and the decrease of the Er3+/Ho3+ luminescent lifetimes with increasing Yb3+ concentration in the CsGd(MoO4)2:Yb3+,Er3+/Ho3+ samples. The luminescence properties of these phosphors suggest their potential possibility for applications in solid-state lighting and displays as well as in c-Si solar energy conversion systems.

Enhanced and Stable Upconverted White-light Emission in Ho3+/Yb3+/Tm3+-doped LiNbO3 Single Crystal via Mg2+ Ion Doping

A strategy to enhance the upconversion white-light intensity via Mg²⁺ ion doping was demonstrated in Ho³⁺/Yb³⁺/Tm³⁺/LiNbO₃ single crystal. It is found Mg²⁺ ion doping affects the crystal field symmetry around RE³⁺ ions and enhance the upconversion emission intensity. Bright white-light is obtained when the Mg²⁺ ion concentration is 0.5 mol% in the melt. And the CIE coordinates are hardly changed with Mg²⁺ ion doping. In addition, the upconversion mechanism is discussed in detail. It is observed the longer lifetimes of intermediate levels result in the lower upconversion photon numbers, which are beneficial to the upconversion process. Therefore, Mg²⁺ ion doped Ho³⁺/Yb³⁺/Tm³⁺/LiNbO₃ single crystals would have potential applications in stable white-light devices and photoelectric instruments.

Synthesis, structure and upconversion luminescence of Yb3+, Ho3+ co-doped Gd3Al5O12 garnet phosphor prepared by the Pechini sol–gel method

A pure-phase phosphor of Gd₃Al₅O₁₂ garnet (GAG) co-doped with Yb³⁺ and Ho³⁺ ions has been synthesized by the Pechini sol–gel method.