The LHPG technique has been successfully applied to the growth of single crystals in fiber shape with a controlled composition and lattice parameter gradient along the fiber axis. The GdTaO4-ErTaO4 system was chosen for having a full solubility range. The obtained fibers had a constant gradient of lattice parameters along the axis with a value of 1.24%/cm for the (4 (4) over bar4) reflection, hence of concentration gradient. Structural characterization results showed that the fibers had a good crystalline quality essential for the optimization of others physical properties. Luminescent characterization showed the behavior of the intensity of green and red luminescence (by 488 nm pumping) as a function of concentration of Er3+ and three processes populating the levels (H-2(11/2), S-4(3/2)) and F-4(9/2) by cross-relaxation energy transfer has been proposed. The results presented show that the compositional gradient and the LHPG technique can be used not only for the growth of crystals with controlled lattice parameter gradients, for potential X-ray diffraction applications, but also as a combinatorial method for the rapid study of material properties as a function of concentration using in situ measurements. (c) 2006 Elsevier B.V. All rights reserved.