Luminescence, energy transfer, colour modulation and up-conversion mechanisms of Yb³⁺, Tm³⁺ and Ho³⁺ co-doped Y₆MoO₁₂

A series of novel up-conversion luminescent Yb³⁺/Ln³⁺ (Tm³⁺, Ho³⁺, Tm³⁺/Ho³⁺)-doped Y₆MoO₁₂ (YMO) nanocrystals were synthesized using the sol-gel method. The consistent spherical morphology of the nanocrystals with different doping ratios was found to be profiting from the homogenisation and rapid agglomeration of the composition in the gel state and calcining process. The X-ray diffraction (XRD) and field-emission scanning electron microscope images were employed to confirm perfect crystallinity and uniform morphology. Photoluminescence spectra and decay curves were used to characterize the optical properties of the synthesized samples. The YMO:Yb³⁺/Ln³⁺ (Tm³⁺, Ho³⁺, Tm³⁺/Ho³⁺) nanocrystals were excited by near-infrared photons and emitted photons distributed in blue, green, and red bands with a wide colour gamut, and even white colour, by optimising the relative doping concentrations of the activator ions. The energy conversion mechanism in the up-conversion process was studied using power-dependent luminescence and is depicted in the energy level diagram. In addition, 70% of the luminescence intensity of YMO can be preserved after annealing at 700 °C, and the temperature sensing was tested in the range 298-498 K. These merits of multicolour emissions in the visible region and good stability endow the as-prepared nanocrystals with potential applications in the fields of optical data storage, encryption, sensing, and other multifunctional photonic technologies.