Green-Emitting Gd3Ga5O12: Tb3+ Nanoparticles Phosphor: Synthesis, Structure, and Luminescence

Luchechko et al. Nanoscale Research Letters (2017) 12:263 DOI 10.1186/s11671-017-2032-x NANO EXPRESS Open Access Green-Emitting Gd3Ga5O12: Tb3+ Nanoparticles Phosphor: Synthesis, Structure, and Luminescence A. Luchechko1*, L. Kostyk1, S. Varvarenko2, O. Tsvetkova1 and O. Kravets1 Abstract Nano- and microceramics of Gd3Ga5O12 garnet doped with 1 mol % Tb3+ ions were synthesized via co-precipitation and high-temperature solid-state reaction methods. X-ray diffraction measurements confirmed the formation of the garnet structure with Ia3d space group in all investigated samples. Atomic force microscopy surface images and grain-size distribution diagrams of Gd3Ga5O12: 1 mol % Tb3+ nanoceramics with 300 and 400 g/mol of polyethylene glycol (PEG) were obtained. The relationship between the content of polyethylene glycol and the particle size of Gd3Ga5O12: Tb3+ phosphors was revealed. An intense broad band (λm = 266 nm) related to spin-allowed 4f 8-4f 75d 1 transitions of Tb3+ ions was found in photoluminescence excitation spectra of Gd3Ga5O12: Tb3+ nanocrystalline ceramics with PEG-300 and PEG-400 at 300 K. The broad excitation band caused by spin-forbidden (λm = 295 nm) 4f-5d transitions in Tb3+ ions was additionally observed in the photoluminescence excitation spectra of Gd3Ga5O12: Tb3+ microceramics. Emission of Tb3+ ions under X-ray and UV excitations is presented by two groups of sharp lines which correspond to 5D3 and 5D4 → 7Fj transitions of Tb3+ ions with the most intense line at 546 nm (5D4 → 7F5). It was established that the increasing of PEG content leads to the decreasing of the X-ray and photoluminescence emission intensities. Keywords: Gd3Ga5O12 garnet, Tb3+ ions, Nano- and microceramics, Nanoparticles, Co-precipitation method, Polyethylene glycol (PEG), Excitation spectra, X-ray luminescence, Photoluminescence Background Garnet materials, both in the bulk and in the nanocrystalline form, have found numerous applications and therefore have great interest for researchers [1]. Gadolinium gallium garnet (Gd3Ga5O12) doped with bismuth is a perspective material owing to its potential applications in the development of blue phosphors, X-ray, and cathodoluminescence screens and scintillators [2, 3]. Furthermore, gadolinium gallium garnet is an important material suitable as a host for luminescent trivalent lanthanide and transition metal ions [4]. Rare earthdoped gadolinium gallium garnet has attracted much attention as an important material for many applications in optoelectronics, laser physics, biomedicine, and other areas [1, 4–6]. The Tb3+ are attractive emitting ions * Correspondence: 1 Department of Sensor and Semiconductor Electronics, Ivan Franko National University of Lviv, Tarnavskogo St. 107, 79017 Lviv, Ukraine Full list of author information is available at the end of the article because of high quantum efficiency related to the large energy gap between the emitting states and the low lying 7 FJ (J = 0, 1, …, 6) ground states that, apart from Gd3+, are the largest within lanthanides [4]. In the last years, nanocrystalline oxide materials have become extremely popular and have gained increasing technological importance. Particular attention has been devoted to the investigation of nano-sized oxide particles that can emit light in an efficient and controlled way [1]. Developing of the fabrication technology of high-quality nanocrystalline powder and ceramics materials also has great interest since the optical properties of nanocrystals strongly depend on their size and conditions of syntheses [5, 6]. The polycrystalline and nanocrystalline ceramic oxide materials, especially with garnet structure, doped with trivalent rare earth, can exceed the single-crystal analogs in some physical properties, such as larger doping concentrations with controllable distribution in the volume © The Author(s). 2017 Open Access This article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. Luchechko et al. Nanoscale Research Letters (2017) 12:263 Page 2 of 6 of material, elevated compositional versatility, and increased mechanical and thermal properties [5–7]. Moreover, the technology of their preparation is more economical compared with the standard crystal grown processes. This paper presents the structural and luminescent properties of Tb3+-doped Gd3Ga5O12 garnets prepared by the co-precipitation method using the aqueous ammonia as the precipitant and polyethylene glycol as the polymeric agent, which change agglomeration of the nanoparticles and facilitation of the surface modification. Comparative analysis of luminescence characteristics of prepared micro- and nanoceramics also was done. Methods Nanopowders of Tb3+-doped Gd3Ga5O12 garnet were prepared by the co-precipitation method in a polyethylene glycol (PEG)-assisted process. In this method, product components precipitate as insoluble salts or hydroxides. Briefly, appropriate stoichiometric quantities of β-Ga2O3, Gd2O3 were used as starting materials. All components were at least 4-N grade of purity. Doping was provided with 1 mol % of Tb4O7. The mix of oxides was dissolved in 15% nitric acid (4 N) through heating to 100 °C. Then a suitable amount of PEG (molecular weight 300, 400 g/mol) was added to the solution. A chemical reaction took place between the obtained nitrates and the polyethylene glycol. After complete dissolving of starting materials and continuous mixing, the mixture was cooled to 0 ± 2 °C with the slow addition of precipitant—8% of ammonia (NH4OH). The precursor was continuously added during mixing in the magnetic mixer till pH of the solution stabilized at 10–11 to ensure small dispersion and homogeneity of deposition. Obtained material was multiple times washed with distilled water till alkaline environment was reached (pH = 7). The final step, separation with Shott’s filter and drying in the vacuum desiccator with humidity absorbent (P2O5) were done. Further drying of the material was held at 40 °C for 12 h in air. Obtained precipitate (Fig. 1) was milled in an agate mortar and annealed at different temperatures (850 °C) for 4 h in the air. Finally, the sintered nanopowders were milled once again in an agate mortar. Nanoceramic pellets (Nano PEG-300, Nano PEG-400) were formed by uniaxially pressing the powders in a steel die (8 mm in diameter) at 150 kg/cm2. Obtained samples were annealed at 1000 °C. Some more details of nanoceramics synthesis are also shown in [8]. Microceramic samples of Gd3Ga5O12 doped with 1 mol % Tb3+ were prepared by high-temperature solidstate reaction method. Gadolinium oxide (Gd2O3), βgallium oxide (β-Ga2O3), and terbium oxide (Tb4O7) (...truncated)