Yttria (Y₂O₃) is one promising hosting material for rare-earth-ion-activated phosphors with applications including amplifiers, lasers, waveguides, X-ray imaging, bioimaging, and field emission or electroluminescent displays due to their luminescent characteristics and stability in high vacuum. In fact, in our most recent study, we have deposited Er-doped Y₂O₃ thin films by radical-enhanced atomic layer deposition (ALD).¹ and demonstrated that the Er incorporated in Y₂O₃ can reach a concentration as high as 10²¹ cm^-3 with outstanding room temperature photoluminescence (PL) at 1.54 µm in thin Er-doped (6-14 at. %) Y₂O₃ films deposited at 350°C.² Meanwhile, nanocrystalline materials (e.g.: nanoparticles, nanotubes, and nanowires) exhibit unique physical properties, in particular, increased luminescence efficiency, which are not observed with their bulk counterparts. Hence, in this talk, we present our recent work on the synthesis of nanotubes of rare earth (Er and Yb) doped Y₂O₃, by a solution synthetic method, with a focus on controlling the spatial distribution of the rare earth ions. The processing temperature, pH, time, addition rate of NaOH, the concentration of yttrium nitrate, and the annealing temperature dictated the formation of metastable Y(OH)_3-x(NO₃)_x complexes thus the nucleation/growth of rare-earch doped Y(OH)₃ nanotubes. The rare-earch doped Y(OH)₃ nanotubes were coverted to rare earth doped yttria by high temperature annealing and the resulting nanotubes had varying rare earth dopant concentrations (0-100%) with sizes ranging from 40-500 nm in diameter and 2-10 µm in length. X-ray diffraction (XRD), scanning electron microscopy (SEM), high resolution transmission electron microsecopy (HRTEM), selective area electron diffraction (SAED), and extended x-ray absorption fine structure (EXAFS) were combined to delineate the structure and composition of these nanotubes. The erbium coordination number and local bonding environment are assessed by synchrotron based EXAFS analysis, and are shown to dictate the measured photoluminescence intensity.³ Their room luminescent properties (PL and catholuminescence, CL) are outstanding and even superior than the thin films synthesized by ALD. Finally, we will discuss their electronic properties and the application of these doped yttria nanostructures as small and compact planar optical amplifier.

References: 1. T.T. Van and J.P. Chang, "Controlled erbium incorporation and photoluminescence of Er-doped Y₂O₃", Applied Physics Letters, 87, 011907 (2005). 2. T.T. Van, J. Hoang, R. Ostroumov, K. L. Wang, J. R. Bargar, J. Lu, H.-O. Blom, and J.P. Chang, “Nanostructure and temperature-dependent photoluminescence of Er-doped Y₂O₃ thin films for micro-optoelectronic integrated circuits”, Journal of Applied Physics, 100, 073512 (2006). 3. T.T. Van, J. R. Bargar, and J.P. Chang, “Er coordianation in Y₂O₃ thin films studied by extended X-ray absorption fine structure”, Journal of Applied Physics, 100, 023115 (2006).