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Nd 3+-doped RE 3 Ga 5 O 12 (RE = Gd, Y, and Lu) nano-crystalline garnets of 40-45 nm in size have been synthesized by a sol-gel method. With the decrease of the RE atom size, the chemical pressure related to the decreasing volumes of the GaO 4 tetrahedral, GaO 6 octahedral and REO 8 dodecahedral units drive the nano-garnets toward a more compacted structure, which is evidenced by the change of the vibrational phonon mode frequencies. The chemical pressure also increases the crystal-field strength felt by the RE 3+ ions while decreases the orthorhombic distortion of the REO 8 local environment. These effects alter the absorption and emission properties of the Nd 3+ ion measured in the near-infrared luminescence range from 0.87 to 1.43 μm associated with the 4 F 3/2 → 4 I J (J = 9/2, 11/2, 13/2) transitions. The 4 F 3/2 luminescence decay curves show non-exponential behavior due to dipole-dipole energy transfer interactions among Nd 3+ ions that increases with pressure.

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.

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.