Synthesis and characterization of Co2+-doped lithium aluminum spinel nanocrystals

doi:10.1016/j.jnoncrysol.2005.05.024

Journal of Non-Crystalline Solids

Volume 351, Issues 27–29, 15 August 2005, Pages 2348-2351

https://doi.org/10.1016/j.jnoncrysol.2005.05.024 Get rights and content

Abstract

In this paper, Co²⁺-doped LiAl₅O₈ nanocrystals were prepared via a citrate sol–gel method. The as-prepared LiAl₅O₈ nanocrystals appear to be single cubical crystalline phase with an average diameter of 15–30 nm. The absorption spectrum of doped Co²⁺ ions in the near-infrared region exhibits a broad absorption band centered at 1400 nm.

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Cited by (10)

Non-stoichiometric Ce-doped LiAl<inf>5</inf>O<inf>8</inf> phosphors: Synthesis, structural and optical properties
2019, Ceramics International
Citation Excerpt :
Particularly, Lithium aluminate LiAl5O8 (LAO) is seen as a promising material for these purposes, because it presents excellent thermochemical and radiation stability, making it a potential candidate for use as a host matrix for active ions, especially rare earth (RE) ones [12–15]. There are several reports on the introduction of transition metal ions such Fe3+ [16], Mn2+ [17], Co3+ [18] and Cr3+ [19] and rare earth ions such Eu3+ [20], Tb3+ [13,21], Ce3+ [22,23] and Dy3+ [22] for applications in luminescent devices and various synthesis methods, such as sol-gel [18], combustion reaction [19], wet chemical methods [24], solid-state reaction [16,22] have been used to produce Lithium aluminates. Also, other factors that there influence on the luminescent properties such as calcination temperature, dopant, and co-dopant concentrations [22,25,26] also could be taken in order to improve the luminescent properties.
Structural and optical properties of non-stoichiometric pure and doped LiAl₅O₈ prepared via a simple sol-gel using glucose were investigated. X-ray diffraction, scanning electron microscopy, and photoluminescence measurements were used to characterize the prepared samples. By employing Ce³⁺ as trivalent ion doped in the LiAl₅O₈ lattice, the effects of non-stoichiometry of Li⁺ on the network parameters and luminescence properties were systematically investigated. A non-stoichiometric in LiAl₅O₈ led to a lattice change and local symmetry distortion. Lattice variation and doping effects, and its relevant defect chemistry had a significant impact on the luminescence properties. The luminescence emission of Ce-doped LiAl₅O₈ phosphors showed an intensity change with variation of Lithium concentration, which is thought to be related to doping effects and variation of lattice parameters. Therefore, with nonstoichiometric control, the luminescence of Ce-doped LiAl₅O₈ phosphors can be well regulated and optimized. Emission lines assigned to Fe³⁺ and Cr³⁺ impurities originated from start reagents used in the sample synthesis were also observed.
Li-self doping effect on the LiAl<inf>5</inf>O<inf>8</inf> luminescent properties
2019, Optical Materials
Citation Excerpt :
LiAl5O8 is a potential host to prepare phosphors due to its thermal, irradiation and chemical stabilities. It presents an inverse spinel crystal structure in cubic lattice that can accommodate doping ions such as external transition metals (Fe3+ [1], Co2+ [2], Mn2+ [3]) and Cr3+ [4] or rare earth ions (Eu3+ [5,6], Tb3+ [7,8], Ce3+ [9,10] and Dy3+ [9]) to obtain the optical properties. To produce doped phosphors based on this host, the main challenge is getting uniform dopant distribution in the final product [11].
The influence of Li self-doping effect on the structural and optical properties of LiAl₅O₈ was investigated. X-ray diffraction (XRD) results indicated the samples present high crystalliny degree and single crystalline phase. Scanning Electron Microscopy (SEM) images showed nanosized particles disposed in agglomerates. X-ray Absorption Near Edge Spectroscopy (XANES) indicated that the Al local geometry is similar for both sets of samples, independent on the Li excess. X-ray Fluorescence (XRF) mapped intrinsic contaminants (Fe and Cr) from the precursors. Photoluminescence (PL) and X-ray Excited Optical Luminescence (XEOL) emission spectra presented broad bands and transitions associated with Fe³⁺, Cr³⁺ and defects from the host. XEOL excitation spectra presented positive edge and luminescent grow tendency with the increase of the excitation energy around the Al K-edge. The observed optical transitions by the excitation with X-rays, ultraviolet and visible were more expressive in the red/near infrared range.
Luminescence investigations on LiAl<inf>5</inf>O<inf>8</inf>:Tb <sup>3+</sup> nanocrystalline phosphors
2011, Current Applied Physics
Citation Excerpt :
Beside these application these materials exhibits good luminescent properties when they are doped with the specific impurities. A considerable amount of work has been carried out in the LiAl5O8 with the rare earth ion like Eu3+ [4], and also with the transition ion dopants like Mn2+, Cr3+, Co2+ and Fe3+ [5–8] etc., but no work could be traced on the photoluminescence properties of the Tb3+-doped LiAl5O8 nanocrystalline phosphors to the best of our knowledge. Tb3+ ion in inorganic compounds is of great importance due to the potential technological applications as functional photonic materials, such as optical fiber amplifiers, lasing medium and frequency-converting devices [9–11].
Tb³⁺-doped porous LiAl₅O₈ nanophosphors were successfully synthesized using a single step combustion method. Structural characterization of the luminescent material was carried out with X-ray diffraction (XRD) analysis and high resolution transmission electron microscopy (HRTEM). Surface composition was estimated from X-ray photoelectron and Auger spectroscopic techniques. The average particle size was estimated as 37 ± 3 nm. Luminescence properties were studied by the photoluminescence spectroscopy. The phosphor showed intense luminescence in the green region due to the magnetic dipole transition of ⁵D₄→⁷F₅ of the Tb³⁺ ion at 543 nm under 241 nm excitation. The intense 4f–4f transitions of Tb³⁺ outshine the luminescence from host which would otherwise deteriorate the color quality of the display device under operation.
Characterization, EPR and photoluminescence studies of LiAl<inf>5</inf>O<inf>8</inf>:Cr phosphors
2009, Solid State Sciences
Citation Excerpt :
This dopant also has its specific use as an active media involving solid-state laser. Spinel structure is classified into the group of crystals to be used as phosphor or magnetic materials and as a laser host medium [4]. The spinel crystals (LiAl5O8) doped with transition metal ions, such as Ni2+ [5], Fe3+ [6], Co2+ [7] have been synthesized.
Red emitting Cr³⁺ doped LiAl₅O₈ powder phosphor was prepared by combustion route using corresponding metal nitrates and urea in a single step. The prepared powder was characterized by X-ray diffraction and surface area measurements were carried out by Brunauer–Emmet–Teller adsorption isotherms. The electron paramagnetic resonance spectrum in the low field regions is typical for isolated Cr³⁺ ions whereas the resonance signal in the high field region with g = 1.95 is due to exchange coupled Cr³⁺–Cr³⁺ pairs. The optical studies show two broad and intense bands characteristic of Cr³⁺ ions in distorted octahedral symmetry. The photoluminescence spectrum gives a narrow red emission at 710 nm corresponding to ^²E_g → ^⁴A_2g transition upon excitation of 562 nm. The crystal field parameter (Dq), Racah inter-electronic repulsion parameters (B and C) and nephelauxetic parameters have been evaluated and discussed.
EPR and luminescence properties of combustion synthesized LiAl<inf>5</inf>O<inf>8</inf>:Mn phosphors
2008, Materials Chemistry and Physics
LiAl₅O₈:Mn²⁺ phosphors have been synthesized by combustion process in a short time (<5 min). X-ray diffractogram confirms that the synthesized material consists of LiAl₅O₈ as main phase. Scanning electron microscopy showed angular plate-like crystals with non-uniform shape. The EPR spectra of Mn²⁺ ions exhibit resonance signals at g ≈ 4.28 and g ≈ 2.0. The signal at g ≈ 2.0 is due to Mn²⁺ ions in an environment close to tetrahedral symmetry, whereas the resonance at g ≈ 4.28 is attributed to the rhombic surroundings of the Mn²⁺ ions. The variation of zero-field splitting parameter (D) with temperature is measured and discussed. The PL spectra exhibit green emission peaks at 505 and 518 nm which are due to the ⁴T₁ (G) → ⁶A₁ (S) transition of Mn²⁺ ions. The EPR study of LiAl₅O₈:Mn²⁺ phosphor gives clear indication of the Mn²⁺ ions occupying more than one site in this phosphor.
Studies of defects in combustion synthesized europium-doped LiAl<inf>5</inf>O<inf>8</inf> red phosphor
2008, Journal of Solid State Chemistry
Europium-doped LiAl₅O₈ red phosphor was prepared using a self-propagating (combustion) synthesis. The formation of crystalline LiAl₅O₈ was confirmed by X-ray diffraction. The morphological aspect of the resulting powders was examined by scanning electron microscopy. Electron spin resonance studies have been carried out in order to study the characteristics of the defect centres and the thermoluminescence (TL) peaks observed in this phosphor. Two types of centres (centre I and centre II) have been identified in LiAl₅O₈:Eu. Centre I is characteristic of a species exhibiting an isotropic g-value 2.0089 with a line width of 70 G and is assigned to a V-centre. Centre II is also characterized by an isotropic g-value 2.0059 with a line width of about 10 G. Centre II is ascribed to a F⁺-centre. A room temperature photoluminescence study shows a strong emission line at 613 nm corresponding to the ⁵D₀→⁷F₂ transition of Eu³⁺ ions.

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Synthesis and characterization of Co2+-doped lithium aluminum spinel nanocrystals

Abstract

Mater. Res. Bull.

J. Alloys Compd.

Opt. Mater.

J. Lumin.

J. Lumin.

J. Chem. Phys.

Philips. Res.

Phys. Chem. Minerals

Science

Bull. Chem. Soc. Jpn.

Synthesis and characterization of Co²⁺-doped lithium aluminum spinel nanocrystals