Nanostructure and luminescence properties of amorphous and crystalline ytterbium–yttrium oxide thin films obtained with pulsed reactive crossed-beam deposition

Abstract

The nanostructure of ytterbium-doped yttrium oxide thin films, produced using pulsed laser ablation of a Yb-Y alloy target together with a pulsed flow of oxygen, is examined using X-ray and electron diffraction as well as Scanning Transmission Electron Microscopy (STEM). As-produced coatings are amorphous and become nanocrystalline cubic yttria after annealing. STEM images taken in the Bright-Field (BF) and in the High-Angle Annular Dark-Field (HAADF) modes reveal different aspects of the nanostructure of yttria. Simulations of the bixbyite structure of yttria indicate that dark spots arranged in a honeycomb structure seen in the STEM-BF mode arise from the absence of oxygen ions at regular crystallographic locations, while those seen on the HAADF images arise from cationic distortions. These results spectacularly exemplify the complementarity of the BF and HAADF imaging modes. Luminescence properties of amorphous and crystalline samples are also studied. Excitation of Yb 3? ions with an infrared (IR) laser diode produce both IR luminescence from excited Yb 3? and visible luminescence from holmium impurities present in the starting materials. Yb 3? emission bands become increasingly narrower as crystallization takes place, testifying for the transition from inhomogeneous to homogeneous crystal field. Increased lifetime and more intense luminescence observed after annealing imply reduced nonradiative relaxation and higher quantum efficiency.

Probability density function of the rate of energy transfer from luminescent ions to a random distribution of traps in the static limit

“…2. The sample is a Yb x Y 1−x 2 O 3 thin film grown by pulsed reactive cross-beam deposition [24]. Because of the low concentration of Yb 3 (x 1.7%), we expect energy migrations from ions to ions over long distance to be negligible, although this hypothesis would need further verifications.…”

“…Hence, we expect a strong multi-exponential decay character to exist owing to the trap density if the hypothesis of static transfer is to be valid. Luminescence decay curves of the excited level of Yb 3 were obtained by collecting the IR luminescence after the excitation from a pulse of the laser diode was sent onto the sample [24]. As seen in Fig.…”

Photofragmentation Pathways for Gas-Phase Lanthanide Tris(isopropylcyclopentadienyl) Complexes

“…Lanthanide oxide thin films have applications in metal-oxide semiconductor field-effect transistors (MOSFETs), − protective coatings, , luminescent materials, − and waveguides. , Lanthanide cyclopentadienyl complexes have been frequently employed to prepare lanthanide oxide thin films by both metal–organic chemical vapor deposition (MOCVD) and atomic layer deposition (ALD) techniques. − For example, Kondo et al deposited Pr 2 O 3 films on silicon substrates with a high dielectric constant of 26 ± 3 using praseodymium tris­(ethylcyclopentadienyl) [Pr­(EtCp) 3 ] precursors, and Blanquart et al used erbium cyclopentadienyl complexes to deposit Er 2 O 3 thin films by ALD. , The high volatility of lanthanide cyclopentadienyl complexes also makes them potential precursors for photolytic laser-assisted metal–organic chemical vapor deposition (LCVD), allowing lower deposition temperatures. It is our goal to better understand the photofragmentation pathways of gas-phase lanthanide cyclopentadienyl complexes in order to better control the purity of thin-film deposition using LCVD.…”