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The CIE (Commission International de I''E'' clairage) chromaticity coordinates were calculated from emission spectra. They were close to the NTSC (National television standard committee) standard value of red emission. The average correlated color temperature (CCT) was found to be 2109 K. Therefore, the MgAl2O4:Cr3 þ phosphor is useful for laser and solid state display applications.
Journal of Science: Advanced Materials and Devices (2018) 464e470 Contents lists available at ScienceDirect Journal of Science: Advanced Materials and Devices journal homepage: www.elsevier.com/locate/jsamd Original Article Photoluminescence and photometric studies of low temperature prepared red emitting MgAl2O4:Cr3ỵ nanophosphors for solid state displays C Pratapkumar a, S.C Prashantha a, *, H Nagabhushana b, **, D.M Jnaneshwara c a b c Research Center, Department of Physics, East West Institute of Technology, VTU, Bengaluru, 560091, India Prof CNR Rao Center for Advanced Materials, Tumkur University, Tumkur, 572103, India Department of Physics, SJB Institute of Technology, VTU, Bengaluru, 560060, India a r t i c l e i n f o a b s t r a c t Article history: Received 19 June 2018 Received in revised form 30 August 2018 Accepted September 2018 Available online 13 September 2018 MgAl2O4:Cr3ỵ (0.01e0.11 mol) doped nanocrystalline powders were prepared by a combustion method at low temperature The Scherer's method was used to estimate crystallite size and values were found to be in the range 20e30 nm and the same was confirmed by transmission electron microscopy (TEM) images The energy band gap of the prepared samples was estimated from diffusion reflection spectra (DRS) and found to be 3.7e4.5 eV The characteristic emission peaks recorded at 17123.3 cmÀ1 and 14727.5 cmÀ1 were attributed to the transitions 4T2/4A2 and 2E/4A2 respectively upon 357 nm excitation The emission intensity increases up to mol % Cr3ỵ particles and then decreases, which may be due to concentration quenching The CIE (Commission International de I'E' clairage) chromaticity coordinates were calculated from emission spectra They were close to the NTSC (National television standard committee) standard value of red emission The average correlated color temperature (CCT) was found to be 2109 K Therefore, the MgAl2O4:Cr3ỵ phosphor is useful for laser and solid state display applications © 2018 The Authors Publishing services by Elsevier B.V on behalf of Vietnam National University, Hanoi This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/) Keywords: MgAl2O4:Cr3ỵ Nanophosphor Diffused reectance Photoluminescence Racah parameters Introduction Materials having inverse spinel with AB2O4 structure with the space group (Fd3m) were effectively used as a host for glow phosphors when doped with transition-metal/rare-earth ions [1,2] Owing to their special physical, chemical and thermal stability they are quite useful in many applications namely oxide fuel cell, sensors, microwave dielectric material, X-ray imaging, solid state displays, environmental monitoring, etc [3] In this type, magnesium aluminate (MgAl2O4) includes cubic oxygen and cations that ingest octahedral or tetrahedral destinations, in which magnesium and aluminum cations occupy 1/8th of the tetrahedral lattices and 1½ of the octahedral sites, with cation to anion ratio 3:4, so that A2ỵ ions and 16 B3ỵ ions capture fully tetrahedral and octahedral sites, * Corresponding author ** Corresponding author E-mail addresses: scphysics@gmail.com (S.C Prashantha), bhushanvlc@gmail com (H Nagabhushana) Peer review under responsibility of Vietnam National University, Hanoi respectively, or A2ỵ ions B3ỵ ions must be placed in 16 octahedral and the second half in the tetrahedral sites [4,5] MgAl2O4 (MP2135 C) based phosphors have attracted great attention of luminescent researchers due to their excellent chemical and physical stability [6,7] In recent years, nanotechnology has been developed as an interdisciplinary field of research It found wide range applications in various fields [8e10] Especially, much attention has been paid for the facile development of efficient luminescent phosphors (excited by blue or near UV light) with high brightness, long lasting, sensitive, energy saving, environmentally friendliness which are of great interest for material scientists, for example to replace conventional uorescent lamps [11,12] Recently, Cr3ỵ activated nanophosphors such as MgAl2O4:Cr3ỵ [5,12e16] LiAl5O8:Cr3ỵ [17], Zn3Al2Ge3O12:Cr3ỵ [18], ZnO:Cr3ỵ [19], ZnAl2O4:Cr3ỵ [13,20], Ba2Mg(BO3)2:Cr3ỵ [21], Ca3Ga2Ge3O12: Cr3ỵ [22], BaZrSi3O9:Cr3ỵ [23], BaAl2O4:Cr3ỵ [24], Mg2SiO4:Cr3ỵ [25] etc were used for the development of tunable lasers, displays and bio imaging because its 3d3 electronic configuration is easily affected by the crystal field environment of ligand anions in various materials https://doi.org/10.1016/j.jsamd.2018.09.002 2468-2179/© 2018 The Authors Publishing services by Elsevier B.V on behalf of Vietnam National University, Hanoi This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/) C Pratapkumar et al / Journal of Science: Advanced Materials and Devices (2018) 464e470 465 MgAl2O4 requires high temperature to form pure phase as we discussed in our previous paper [26] However it is remained challenging for the synthesis of MgAl2O4 at low temperatures in its pristine or doped form In the present investigation, MgAl2O4:Cr3ỵ (1e11 mol %) was prepared by solution combustion process at very low temperature (280 C), which is simple, fast and safe We reported the preparation of MgAl2O4:Dy3ỵ (1e11 mol %) earlier [26] at the same temperature Also, attention is paid to the inuence of Cr3ỵ doping on photoluminescence properties Experimental Magnesium nitrate (Mg(NO3)2: 99.99%, Sigma Aldrich), aluminium nitrate (Al(NO3)3: 99.99%, Sigma Aldrich) and chromium nitrate (Cr(NO3)3: 99.9%, Sigma Aldrich) and lab made oxalyl dihydrazide (ODH) were used as oxidizers and fuel, respectively, for the preparation of MgAl2O4:Cr3ỵ (1e11 mol %) nanophosphors All the starting materials for were taken in stoichiometric ratios [F/ O ¼ 1] with minimum quantity of double ionized water mixed well in a petri dish using magnetic stirrer and the dish containing a homogeneous mixture was placed in a pre-heated muffle furnace The stoichiometry of the redox mixture used for the combustion synthesis was calculated based on the total oxidizing and reducing valencies of the compounds The solution initially boiled and ignites at one spot with liberation of large amount of gaseous products (oxides of nitrogen and carbon) The combustion propagated throughout the reaction mixture with the formation of white powder Similar procedure was used for other doping concentrations, and the detailed synthesis procedure has been reported elsewhere [27,28] The balanced chemical equation for the MgAl2O4:Cr3ỵ (1 mol %) is given as follows 990 Mg(NO3)2 ỵ 20 Al(NO3)3 ỵ 1234C2H6N4O2 ỵ 10 Cr(NO3)3 ẳ 10 Mg0.99Al2O4:Cr0.01 þ 3503 N2 þ 3702H2O þ 2468 CO2 The structural parameters of Cr3ỵ doped MgAl2O4 nanoparticles were examined by X-ray diffractometer (XRD) (Shimadzu, operating at 50 kV and 20 mA by with CuKa radiation at a wavelength of 1.541 Å) The lattice parameters were estimated with the Rietveld analysis using the FULLPROF software package and the packing diagram was drawn by using diamond software The structure, crystallinity and morphology were performed with Hitachi table top (SEM) (Model TM 3000) (accelerating voltage up to 20 kV using Tungsten filament) and JEOL (TEM), JEM-2100 (accelerating voltage up to 200 kV, LaB6 filament) equipped with EDS having 1.5 Å resolutions respectively The diffuse reflectance spectra were recorded using UV-VIS spectrophotometer (Shimadzu UV-2600) using BaSO4 as a reference The room temperature photoluminescence (PL) spectra were recorded on Horiba (model Fluorolog-3) Spectroflourimeter at RT with Fluor Essence™ software and supplied with a flash 450 W Xenon lamp as excitation source Results and discussion Powder X-ray diffraction (PXRD) patterns of the MgAl2O4 doped with Cr3ỵ (1e11 mol %) is shown in Fig Diffraction peaks were well indexed to pure cubic phase (JCPDS card No 21-1152) with space group Fd3m (O7h , No 227) The acceptable percentage difference in ionic radii [26] was found to be 15.3% (