Intense red up-conversion luminescence and dynamical processes observed in Sc2O3:Yb3+,Er3+ nanostructures

The intense red up-conversion luminescence in Sc₂O₃:Yb³⁺,Er³⁺ synthesized using a biphasic solvothermal (ST) method was observed upon laser diode pumping at 980 nm.

Size of the rare-earth ions: a key factor in phase tuning and morphology control of binary and ternary rare-earth fluoride materials

An IL based solvothermal route to prepare RE ion doped luminescent binary/ternary fluoride nanomaterials. Size of the RE ions tunes the nature of the product, crystal phase, lattice strain and morphology, effecting the luminescence properties.

Morphology evolution and pure red upconversion mechanism of β-NaLuF4 crystals

A series of β-NaLuF₄ crystals were synthesized via a hydrothermal method. Hexagonal phase microdisks, microprisms, and microtubes were achieved by simply changing the amount of citric acid in the initial reaction solution. Pure red upconversion (UC) luminescence can be observed in β-NaLuF₄:Yb³⁺, Tm³⁺, Er³⁺ and Li⁺ doped β-NaLuF₄:20% Yb³⁺, 1% Tm³⁺, 20% Er³⁺. Based on the rate equations, we report the theoretical model about the pure red UC mechanism in Yb³⁺/Tm³⁺/Er³⁺ doped system. It is proposed that the pure red UC luminescence is mainly ascribed to the energy transfer UC from Tm³⁺:³F₄ → ³H₆ to Er³⁺:⁴I_11/2 → ⁴F_9/2 and the cross-relaxation (CR) effect [Er³⁺:⁴S_3/2 + ⁴I_15/2 → ⁴I_9/2 + ⁴I_13/2] rather than the long-accepted mechanism [CR process among Er³⁺:⁴F_7/2 + ⁴I_11/2 → ⁴F_9/2 + ⁴F_9/2]. In addition, compared to the Li⁺-free counterpart, the pure red UC luminescence in β-NaLuF₄:20% Yb³⁺, 1% Tm³⁺, 20% Er³⁺ with 15 mol% Li⁺ doping is enhanced by 13.7 times. This study provides a general and effective approach to obtain intense pure red UC luminescence, which can be applied to other synthetic strategies.

Phase selective synthesis of quantum cutting nanophosphors and the observation of a spontaneous room temperature phase transition

Oxygen-free Eu(3+)-doped NaGdF4 nanocrystals with high quantum cutting efficiency are accessible at low temperatures (room temperature to 80 °C) using task-specific ionic liquids (ILs) as structure directing agents and only water as solvent. Selective tuning of the shape, morphology and, most importantly, the crystal phase of the host lattice is achieved by changing the alkyl side length, the H-bonding capabilities and the concentration of 1-alkyl-3-methylimidazolium bromide ILs, [C(n)mim]Br. When using [C2mim]Br, hexagonal NaGdF4 nanoparticles are obtained. In the case of methylimidazolium bromides with longer pendant alkyl chains such as butyl (C4), octyl (C8) or decyl (C10), extremely small nanoparticles of the cubic polymorph form, which then convert even at room temperature (RT) to the thermodynamically favored hexagonal modification. To the best of our knowledge, this kind of spontaneous phase transition is not yet reported. The hexagonal nanomaterial shows a substantial quantum cutting efficiency (154%) whilst in the cubic material, the effect is negligible (107%). The easy yet highly phase selective green synthesis of the materials promises large scale industrial application in environmentally benign energy efficient lighting.

Shape-controllable synthesis and enhanced upconversion luminescence of Li+ doped β-NaLuF4:Yb3+,Ln3+ (Ln = Tm, Ho) microcrystals

UC luminescence intensities of blue and green emissions are significantly enhanced via Li⁺ doping.