Nanocrystalline Lu3Ga5O12 garnets doped with Tm(3+)/Yb(3+) ions have been synthesized by a low cost and environmentally benign sol-gel technique and characterized for their structural, Stokes and anti-Stokes luminescence properties. The diffuse reflectance spectra of doped Lu3Ga5O12 nano-garnets have been measured to derive the partial energy level structure of Tm(3+) and Yb(3+) ions and possible energy transfer channels between them. Upon laser excitation at 473 nm, weak red and intense near-infrared Stokes emissions have been observed in the nano-garnets. The decay curves of (3)H4 and (1)G4 levels of Tm(3+) ions and the (2)F5/2 level of Yb(3+) ions have been measured upon resonant laser excitation and are found to be non-exponential in nature due to multipolar interactions. In order to know the kind of multipolar interaction among optically active ions, the decay curves are analyzed through the generalized Yokota-Tanimoto model. Moreover, under 970 nm laser excitation, intense blue anti-Stokes emission is observed by the naked eye in Tm(3+)-Yb(3+) co-doped Lu3Ga5O12 nano-garnets. The results show that as-synthesized nano-garnets may be useful in the field of phosphors and photonics.

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Nano-crystalline lutetium gallium garnets co-doped with Dy3+ and Sm3+ ions have been synthesized via a sol–gel method and their structural, morphological and luminescence properties have been characterized.

Trivalent dysprosium-doped Lu3Ga5O12 nano-garnets have been prepared by sol-gel method and characterized by X-ray powder diffraction, high-resolution transmission electron microscopy, dynamic light scattering, and laser excited spectroscopy. Under a cw 457 nm laser excitation, the white luminescence properties of Lu3Ga5O12 nano-garnets have been studied as a function of the optically active Dy3+ ion concentration and at low temperature. Decay curves for the 4F9/2 level of Dy3+ ion exhibit non-exponential nature for all the Dy3+ concentrations, which have been well-fitted to a generalized energy transfer model for a quadrupole-quadrupole interaction between Dy3+ ions without diffusion. From these data, a simple rate-equations model can be applied to predict that intense white luminescence could be obtained from 1.8 mol% Dy3+ ions-doped nano-garnets, which is in good agreement with experimental results. Chromaticity color coordinates and correlated color temperatures have been determined as a function of temperature and are found to be within the white light region for all Dy3+ concentrations. These results indicate that 2.0 mol% Dy3+ ions doped nano-garnet could be useful for white light emitting device applications.

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