Studies on phase stability, mechanical, optical and electronic properties of a new Gd2CaZnO5 phosphor system for LEDs

Abstract

A new ternary oxide Gd 2 CaZnO 5 having interesting structural, mechanical, electronic and optical properties is synthesized and is studied in detail using density functional theory. The analysis revealed two polymorphs: orthorhombic and tetragonal; the orthorhombic phase was found to be the most stable structure under ambient conditions. A high-pressure (hydrostatic) phase transition to the tetragonal phase is predicted at about 4 GPa. This is one of very few reports that depict the phase transition of oxide materials under pressure. The calculated results are in agreement with the X-ray diffraction studies supported by Rietveld analysis. Analysis of the optical properties revealed both polymorphs to be direct-gap semiconductors with low dielectric constants. The calculated elastic constants of both phases satisfy the mechanical stability criteria. It is also identified that the half-filled 4f orbital of Gd induces a strong magnetic spin polarization in the host oxide lattice indicating that the material could be effectively used in versatile applications ranging from biomedical devices to light emitting diodes.Inorganic luminescent materials (also called "phosphors") have become the subject of renewed research and development due to the requirement of efficient color display systems for next generation lighting and display devices.1-3 Especially, a family of oxide crystals doped with rare-earth ions have become candidate materials for such display devices due to their highly efficient emission properties which are attributed to the sharp f-f transitions in the visible spectrum. 4 For example, ternary oxides defined by R 2 AMO 5 with R = rare-earth, A = alkaline-earth and M = Cu or Zn atoms are found to have the desired luminescent properties for efficient color tunability. 5-10This family of ternary oxides having large band gaps can serve as good luminescent hosts in accommodating rare-earth ions as dopants and thereby yielding effective luminescence with high quantum efficiency.

UV-A and UV-B excitation region broadened novel green color-emitting CaGd2ZnO5:Tb3+ nanophosphors

“…In this context, we developed a Tb 3+ ions activated green color-emitting novel CaGd 2 ZnO 5 (CGZO) nanophosphors with the enhanced broadened excitation region over the UV and near-UV (NUV) ranges. Xu et al demonstrated this novel CGZO host lattice with GdO 7 , CaO 11 , and ZnO 5 polyhedral units based on the ARE 2 MO 5 structure, 16 and our group have recently established the richness of this host lattice when doped with Eu 3+ ions. 17 To the best of our knowledge, no reports have been found so far on the luminescent properties of Tb 3+ ions activated CGZO host lattice.…”

Versatile properties of CaGd2ZnO5:Eu3+ nanophosphor: its compatibility for lighting and optical display applications

“…For instance, A 4 RE 6 (XO 4 ) 6 O 2 14 and ARE 2 MO 5 19 (A = alkaline earth elements, RE = rare earth elements, X = Si or P, and M = Co, Ni, Cu, Zn, Pd or Pt) compounds are established as having the desired luminescent properties for the fabrication of efficient optical systems. Xu et al 20 In this paper, we reported the phase stability and annealing temperature effect on the transmittance and luminescent properties of CGZO:Eu 3+ nanophosphors obtained via a sol-gel process for the first time. The structural, morphological, and optical properties were evaluated by X-ray diffraction (XRD) patterns, scanning electron microscope (SEM) images, and UVvisible transmittance spectra, respectively.…”

“…Very recently, Xu et al20 reported the novel CGZO host lattice, and so its t JCPDS card is not available. Very recently, Xu et al20 reported the novel CGZO host lattice, and so its t JCPDS card is not available.…”

Luminescence properties of Dy3+ ions activated novel warm white-light emitting CaGd2ZnO5 nanophosphors

“…According to our earlier reports [15,16], the optimal annealing temperature was found to be at 1200 ºC and the dilute concentrations of doping ions did not show any considerable effect on the crystallite size and phase purity [16]. Recently, Xu et al [17] reported the crystal structure of the novel CGZO host lattice, but the JCPDS card is not available till now. The acquired XRD pattern was in well agreement with the data of Xu et al which confirmed the orthorhombic phase of typical CGZO diffraction peaks with the space group of Pnma, and the lattice constants are a ¼ 12.325 Å, b ¼ 5.545 Å, and c ¼ 7.3225 Å.…”