This work initiated a study on the preparation of assembled-spheres YVO4:(Ln3+, Bi3+) (Ln = Eu, Sm, Dy, Ho), in which Bi3+ co-doping of a lower content, aims to achieve emission tailored for many applications by supressing the serious changes in host structures when higher concentrations of Bi3+ are involved. The formation of assembled-spheres is beneficial from the simultaneous dissolution of the starting Bi and Ln salts with the use of ethylene glycol. As a result, all assembled-spheres are featured by low surface absorbents and little interior lattice defects, which decreased the nonradiative rate to give a luminescence performance superior to other morphologies like cereal-like architectures. Further, four paths were applied to achieve the tunable multicolour-emission in these assembled-spheres, which include: (i) selecting the dopant Ln3+ with characteristic emissions; (ii) varying the concentration of dopant Ln3+; (iii) co-doping Ln3+/Bi3+ with dual emissions from Bi3+ and Ln3+; and (iv) adjusting the excitation wavelength. These tunable multicolour-emissions were demonstrated to be the consequence of the energy transfer process from the VO43−group to Ln3+ in YVO4:Ln3+ or those from Bi3+ and the VO43−group to Ln3+ in the presence of lower Bi3+ content, as followed by a surprising red-shift of the absorption edge and extension of the luminescence lifetimes of Ln3+. The diverse approaches found in this work for emission tailoring are fundamentally important and may provide a general way to achieve multicolour-tunable emission for many applications.
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