Journal of Science: Advanced Materials and Devices (2019) 531e537 Contents lists available at ScienceDirect Journal of Science: Advanced Materials and Devices journal homepage: www.elsevier.com/locate/jsamd Original Article Photoluminescence and photocatalytic properties of novel Bi2O3:Sm3ỵ nanophosphor S Ashwini a, b, S.C Prashantha b, *, Ramachandra Naik c, **, Yashwanth V Naik d, H Nagabhushana d, K.N Narasimhamurthy e a Department of Physics, Channabasaveshwara Institute of Technology, Gubbi 572216, India Research Center, Department of Science, East West Institute of Technology, VTU, Bengaluru 560091, India Department of Physics, New Horizon College of Engineering, Bengaluru 560103, India d Prof CNR Rao Center for Advanced Materials, Tumkur University, Tumkur 572103, India e Department of Physics, Government First Grade College, Tumkur 572102, India b c a r t i c l e i n f o a b s t r a c t Article history: Received May 2019 Received in revised form 18 August 2019 Accepted September 2019 Available online 14 September 2019 The current work involves studies of the synthesis, characterization and photoluminescence for Sm3ỵ (1 e11 mol%) doped Bi2O3 nanophosphors (NPs) by a solution combustion method The average particle size was determined using powder X-ray diffraction (PXRD) and found to be in the range of 13e30 nm The KubelkaeMunk (KeM) function was used to assess the energy gap of Sm3ỵ doped Bi2O3 nanophosphors which was found to be 2.92e2.96 eV From the Emission spectra, the JuddeOfelt parameters (U2 and U4), the transition probabilities (AT), the quantum efficiency (h), the luminescence lifetime (tr), the colour chromaticity coordinates (CIE) and the correlated colour temperature (CCT) values were estimated and discussed in detail The CIE chromaticity co-ordinates were close to the NTSC (National Television Standard Committee) standard value of Orange emission Using the LangmuireHinshelwood model and Acid Red-88, the photocatalytic activity results showed that Bi2O3:Sm3ỵ NPs are potential materials for the development of an efficient photocatalyst for environmental remediation The obtained results prove that the Bi2O3:Sm3ỵ nanophosphors synthesised by this method can potentially be used in solid state displays and as a photocatalyst © 2019 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: Bi2O3:Sm3ỵ Photoluminescence JuddeOfelt CIE CCT Introduction Lanthanide ions doped (Ln3ỵ) nanophosphors (NPs) have gained massive attention owing to their potential applications in various fields ranging from display [1], solar cells [2], bio-imaging [3], solid state lasers [4], remote photo activation [5], temperature sensors [6] and drug release [7] Furthermore, NPs should possess superior physicochemical characteristics, such as long lifetimes, large anti-Stokes shifts, high penetration depth, low toxicity, as well as high resistance to photo bleaching [8] Bismuth is the only nontoxic heavy metal that can easily be purified in large quantities [9] * Corresponding author ** Corresponding author E-mail addresses: scphysics@gmail.com (S.C Prashantha), rcnaikphysics@gmail com (R Naik) Peer review under responsibility of Vietnam National University, Hanoi The semiconductors such as Bi2MoO6, BiOX (X ¼ Cl, Br, I), BiVO4 and Bi2O3 have a high refractive index and excellent properties for visible light absorb ion, photoluminescence, dielectric permittivity, photoconductivity, large oxygen ion conductivity, and, noteworthy, for photocatalytic activity [10e12] At present, the photocatalysis technology has been anticipated to be a perfect “green” technology by the usage of solar energy in many fields such as, water-splitting [13], solar cell [14], water and air purification, organic waste degradation [15], CO2 reduction [16] etc The decomposition of dye contaminants in contaminated water, as a branch of photocatalysis, has attracted great attention To date, with the exception of intensive research on conventional photocatalysts such as TiO2, ZnO, ZrO2 and other semiconductors with a wide band gap [17], the finding out of new photocatalysts with sturdy degradation abilities has become additionally important Thus, we can consider Bi2O3 as a suitable host material, which is having all these features Bismuth oxide (Bi2O3) is a semiconductor with attractive optical and electronic properties Because of these properties, Bi2O3 has https://doi.org/10.1016/j.jsamd.2019.09.001 2468-2179/© 2019 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/) 532 S Ashwini et al / Journal of Science: Advanced Materials and Devices (2019) 531e537 become an important material for several applications such as fuel cells [18], photocatalysts [19], gas sensors [20], and electronic components [21] Another significant characteristic of Bi2O3 is its polymorphism, which results in polymorphic forms (a, b, g, d and u) with different structures and properties [22], among them monoclinic a which is stable at room temperature and face-centered cubic d that is stable at high temperature There are various methods available for the synthesis of Bi2O3 nanophosphors viz., sonochemical, microwave irradiation, hydrothermal, chemical vapour deposition, micro-emulsion, surfactant thermal strategy, solegel approach, solution combustion and electro-spinning [23,24] In this work we report the synthesis of Bi2ÀxO3:Smx (x ¼ 0.01 to 0.11) NPs via a simple low temperature solution combustion method Compared with the conventional methods adopted for synthesis, the solution combustion method is advantageous in view of its low temperature and reduced time consumption which result in a high degree of crystallinity and homogeneity The synthesised nanophosphor is characterized by PXRD and DRS The effect of Sm3ỵ doping on the photoluminescence properties were studied in detail for their possible usage in display applications Results and discussion 3.1 PXRD studies Fig shows the Powder X-ray diffraction (PXRD) pattern of undoped and Sm3ỵ (1e11 mol%) doped Bi2O3 NPs All the recorded peaks were indexed to the Cubic phase of Bi2O3 (JCPDS card No 521007, Space Group: Fm-3m (no.225)), suggesting high purity and crystallinity of the synthesized powders As the acceptable percentage difference Dr (ionic radii) [27] is less than 15% between Bi3ỵ and Sm3ỵ ions, Sm3ỵ ions substitute the Bi3ỵ ions in the Bi2O3 host Dr ẳ 2.1 Synthesis of Bi2ÀxO3:Smx (x ¼ 0.01 to 0.11) The synthesis of Bi2ÀxO3:Smx (x ¼ 0.01 to 0.11) via solution combustion method was made using analytical grade Bismuth nitrate (Bi(NO3)3$5H2O: 99.99%, Sigma Aldrich Ltd.), Samarium nitrate (Sm(NO3)3$6H2O: 99.99%, Sigma Aldrich Ltd) as dopant and Urea as fuel In a cylindrical Petri dish (300 ml), the aqueous solution containing a stoichiometric quantity of reactants were taken such that Oxidizer (Bi (NO3)3$5H2O) to Fuel (Urea) ratio is (O/F ¼ 1) [25] and introduced into a pre heated muffle furnace at temperature of 400 ± 10 C Thermal dehydration of the reaction mixture takes place and auto-ignites with liberation of gaseous products resulting in the nano powders Finally, the so-prepared powders were calcined at 600 C for h The theoretical equation, assuming complete combustion of the redox mixture used for the synthesis of Bi2O3, can be written as: (2) For Coordination number CN equal to 6, the radius of the host cation Rh (CN) is 1.03 Å, and the radius of the doped ion Rd (CN) is 0.958 Å The calculated Dr is found to be 6.99% [28] The average crystallite size (D) was calculated by using Scherer's formula [29] Dẳ Experimental Rh CNị Rd CNị Rh ðCNÞ 0:9l bcos q (3) where l represents the wavelength of X-rays (1.54 Å), q; the incident angle, and b; the full width at half maximum (FWHM) of the XRD peaks Table gives the crystallite sizes of the Bi2O3:Sm3ỵ (1e11 mol%) samples These are in the range of 13e30 nm which indicates that, as doping concentration increases, crystallite sizes decrease 3.2 Diffuse reflectance spectroscopy studies To evaluate the energy band gap, the diffuse reectance spectra (DRS) of Bi2O3:Sm3ỵ NPs were carried out and shown in Fig The spectra mainly exhibit absorption at ~410 nm which is À Á BiNO3 ị3 $5H2 O ỵ 5CH4 N2 O/Bi2 O3 þ 8N2 þ 5CO2 þ 20H2 O (1) 2.2 Photocatalytic activity of Bi2O3:Sm3ỵ At room temperature, the experiment was conducted in a reactor by utilizing a 125 W mercury vapour lamp as the UV light source (l ¼ 254 nm) Using Acid red dye 88 (AR-88) as a model dye, the UV light photocatalytic activities of Bi2O3:Sm3ỵ NPs were evaluated In this experiment, 30 mg of synthesized Bi2O3:Sm3ỵ NPs was dissolved completely into 10 ppm of AR-88 dye solution and stirred continuously to form a uniform solution At each 15 min, ml of the dye solution was inhibited and tested by a UVeVis spectrophotometer by means of the typical adsorption band at 510 nm after centrifugation for the computation of the disintegration of dye [26] 2.3 Characterization Crystal morphology of the synthesised NPs was determined by PXRD using X-ray diffractometer (Shimadzu) (V-50 kV, I-20 mA, l1.541 Å, scan rate of 2 minÀ1) Photoluminescence studies are made using Horiba (model fluorolog-3, xenon-450 W) Spectroflourimeter at Room Temperature Fluor Essence™ software is used for spectral analysis DRS studies of the samples were performed using Shimadzu UV-2600 in the range 200e800 nm Fig PXRD patterns of undoped and Sm3ỵ (1e11 mol%) doped Bi2O3 NPs Table Crystallite size of Bi2O3:Sm3ỵ Sl no Compound Bi2O3:Sm3ỵ: Bi2O3:Sm3ỵ: Bi2O3:Sm3ỵ: Bi2O3:Sm3ỵ: Bi2O3:Sm3ỵ: Bi2O3:Sm3ỵ: Crystallite size (nm) mol% mol% mol% mol% mol% 11 mol% 23.535 22.553 19.426 16.640 13.243 13.178 S Ashwini et al / Journal of Science: Advanced Materials and Devices (2019) 531e537 Diffuse Reflectance (%) 80 533 3+ Bi2O3:Sm (1-11 mol %) 60 40 20 mol % mol % mol % mol % mol % 11 mol % 200 300 400 500 600 700 800 Wavelength (nm) Fig Excitation spectra of Bi2O3:Sm3ỵ (3, & mol%) NPs (lemi ¼ 610 nm) Fig DRS of Sm3ỵ (1e11 mol%) doped Bi2O3 NPs characteristic for the absorption of Sm3ỵ ions [30] The KubelkaeMunk relation was adopted to calculate the band gap of the NPs [31], À n FR ịhn ẳ C hn Eg (4) 3.3 Photoluminescence studies Fig shows the excitation spectra of Bi2O3:Sm3ỵ NPs for 3, and mol% The spectra were taken in the range of 360 nme500 nm and Fig Emission spectra of Bi2O3:Sm3ỵ (1e11 mol%) (lexc ẳ 465 nm) PL Intensity (a u.) where FðR∞ Þ is the KubelkaeMunk function, hn; the photon energy, C; a constant, Eg ; the optical energy band gap, n; an exponent which value depends on the nature of the inter band electronic transition, viz., n ẳ ẵ (direct allowed transition), n ẳ (indirect allowed transition), n ¼ 3/2 (direct forbidden transition) and n ¼ (indirect forbidden transition) [24] Direct or indirect transitions are “allowed” transitions, if the momentum matrix element characterizing the transition is different from zero This means that the transition can hold for sure if sufficient energy is given to the particle (e.g electron) involved in the process Direct or indirect transitions are “forbidden” transitions, if the momentum matrix element characterizing the transition is equal to zero The transition cannot hold even if sufficient energy is given However, a forbidden transition can sometimes become allowed Sometimes a transition can be forbidden in first order (first order perturbation theory) but it becomes allowed in second order (second order perturbation theory) [32] As Bi2O3 is a direct band gap material, from the extrapolation of the line ẵFR ịhn2 to zero (Fig 3), the Eg of the synthesised NPs was found to be in the range of 2.92e2.96 eV, indicating that the present material can be a promising photocatalyst since it can absorb UV as well as the visible region of solar light 1x10 8x10 6x10 4x10 5 Sm3+ Concentration (mol%) Fig Energy gap of Bi2O3:Sm3ỵ NPs Fig Variation of PL intensity with Sm3ỵ concentration 11 534 S Ashwini et al / Journal of Science: Advanced Materials and Devices (2019) 531e537 Table JeO intensity parameters and radiative properties of Sm3ỵ doped Bi2O3 NPs Phosphor Bi2O3:Sm3ỵ mol% mol% mol% mol% mol% 11 mol% JeO intensity parameters (10À20 cm2) U2 U4 0.41059 0.401301 0.351343 0.386104 0.354646 0.392754 0.361985 0.495693 0.323457 0.347901 0.347472 0.417446 Transitions AR (sÀ1) ANR (sÀ1) AT (sÀ1) tr (ms) h (%) 71.316 69.703 61.025 67.063 61.599 68.218 24.025 23.482 20.558 22.592 20.752 22.982 95.341 93.185 81.584 89.656 82.351 91.199 10.489 10.731 12.257 11.154 12.143 10.965 74.8 74.8 74.8 74.8 74.8 74.8 G5/2 / 6H5/2 G5/2 / 6H7/2 G5/2 / 6H9/2 exhibit bands at 365 nm (6H5/2 / 4D3/2, 5/2), at 395 nm (6H5/2 / 4F7/ 6 2), at 418 nm ( H5/2 / M19/2), at 448 nm ( H5/2 / G9/2), at 465 nm 6 ( H5/2 / I13/2) and at 488 nm ( H5/2 / I11/2) which are attributed to the 4f-4f transition of Sm3ỵ [33] Among these, the prominent transition at 465 nm (6H5/2 / 4I13/2) was taken to explicate the emission spectra of the NPs Fig shows the emission spectra of Bi2ÀxO3:Smx (x ¼ 0.01 to 0.11) calcined at 600 C excited under 465 nm The spectra consist of four typical transition emission bands centered at 565 nm (yellow), 616 nm (orange), 653 nm (orange red) and 713 nm (red) which are due to 4G5/2 / 6H5/2, 4G5/2 / 6H7/2, 4G5/2 / 6H9/2 and 4G5/2 / 6H11/2 respectively Actually at excitation, the doped ions are excited to the higher energy state 4H9/2 from which they relax non-radiatively to the metastable state 4G5/2 through the 4F7/2, 4G7/2, and 4F3/2 levels But 4H9/ and G5/2 correspond to very close and fast non-radiative relaxations So the spectra will have the four transition bands from 4G5/2 Among all the emitted transitions, 4G5/2 / 6H7/2 (616 nm) is the most prominent one with strong orange emission which is partly magnetic dipole and partly electric dipole 4G5/2 / 6H9/2 (653 nm) is purely electric dipole and in this study the intensity of the electric dipole transition is less compared to that of the magnetic dipole one, indicating the symmetry behaviour of Sm3ỵ ions in the host Bi2O3 [34,35] The variation of the PL intensity with respect to the Sm3ỵ dopant concentration is shown in Fig The PL intensity at 616 nm emission increases up to mol% with the increase of Sm3ỵ content and, subsequently, it decreases owing to concentration quenching The energy of the phosphor is lost due to non-radiative (or also multi phononassisted non-radiative) transitions by the incorporation of Sm3ỵ in the host or Sm3ỵ-Sm3ỵ interaction when excited through vacancies The total radiative transition probability (AT ) for an excited state j0 J is transition [37] given by formula: AT jJị ẳ X AR j J À jJ (6) jJ The radiative lifetime ðtr Þ of the excited state j0 J can be obtained by [38] À Á tr j0 J ¼ AR ðjJÞ (7) The luminescence quantum efficiency (h) can be calculated by the relation [39] and was found to be ~75% for the present phosphor: 3.4 Judd Ofelt (JeO) analysis Quantum efficiency is an important parameter which determines the efficiency of nanophosphors for the applications of display devices The electric-dipole (ED) and magnetic-dipole (MD) transitions are generally used in the investigation of rare earth ions doped luminescent materials However, it is challenging to calculate the JeO intensity Ut (t ¼ 2, 4, 6) parameters for powder materials because the absorption spectra of powder materials can hardly be recorded The radiative transition probabilities (AR ) from an excited state j0 J to the final state jJ are related to forced electric dipole transitions and they may be written as a function of the JeO intensity parameters: AR ! À Á2 n n2 ỵ 64p4 w Sed ỵ n Smd j J jJ ẳ 3h2J ỵ 1ị À 0 Á (5) where, Sed and Smd are the electric and magnetic dipole strengths, respectively, wJ is the wavenumber of the respective electronic transition, h is Planck's constant, n is the effective refractive index of the nanophosphor [36] Fig (a) CIE chromaticity diagram of Bi2O3:Sm3ỵ NPs (b) CCT diagram of Bi2O3:Sm3ỵ NPs S Ashwini et al / Journal of Science: Advanced Materials and Devices (2019) 531e537 0.10 (a) Bi2O3: Sm1mol% Min 15 Min 30 Min 45 Min 60 Min (b) Bi2O3: Sm3 mol% 0.10 Min 15 Min 30 Min 45 Min 60 Min 0.08 0.06 Absorbance Absorbance 0.08 0.04 0.06 0.04 0.02 0.02 0.00 350 0.00 400 450 500 550 600 350 650 400 450 (c) Bi2O3: Sm5mol% 0.10 600 650 0.06 0.04 Min 15 Min 30 Min 45 Min 60 Min 0.10 0.08 Absorbance Absorbance 550 (d) Bi2O3: Sm7mol% Min 15 Min 30 Min 45 Min 60 Min 0.08 0.02 0.06 0.04 0.02 0.00 0.00 350 400 450 500 550 600 350 650 400 450 (e) Bi2O3: Sm9 mol% Min 15 Min 30 Min 45 Min 60 Min 0.15 Absorbance 0.10 0.05 550 600 650 Min 15 Min 30 Min 45 Min 60 Min (f) Bi2O3: Sm11 mol% 0.10 0.05 0.00 0.00 350 500 Wavelength(nm) Wavelength(nm) Absorbance 500 Wavelength(nm) Wavelength(nm) 0.15 535 400 450 500 550 600 650 350 400 450 500 550 600 650 Wavelength(nm) Wavelength(nm) Fig Absorption spectra of Acid Red-88 (AR-88) with Bi2O3:Sm3ỵ NPs catalysts under UV light irradiation AR A h¼ ¼ R AR ỵ ANR AT (8) Table gives the results of JeO intensity parameters (U2 and U4) and radiative properties of Bi2O3:Sm3ỵ nanophosphors that are calculated from the emission spectra From the results it is clear that the U2 and U4 values are comparatively high due to the fact that the samples generally possess higher fractions of the rare earth ions on the surface of the nano crystals compared to the bulk counterparts [40] The parameter U2 is related to the short range impact in the vicinity of the rare earth Sm3ỵ ion and U4 is related to the long range impact AR and tr were calculated from the emission spectra The quantum efficiency (h) is calculated with equation (8) and found to be equal to 74.8% as shown in Table An increase in quantum efficiency indicates a better applicability for display devices It was observed that 4G5/2 / 6H7/2 transition of Sm3ỵ doped Bi2O3 NPs dominates the intensity emitted by the NPs in the emission spectra The results infer that the current NPs can be utilized for display devices [38] 3.5 CIE and CCT analysis “Commission International de i’Eclairage (CIE) 1931 standards” were used to calculate the colour coordinates of Bi2ÀxO3:Smx (x ¼ 1e11 mol%) from the emission spectra In the colour space, coordinates (x, y) are used to specify the colour quality and to evaluate the phosphors performance These coordinates are the most prominent parameters Fig 7(a) shows the CIE 1931 chromaticity diagram for Bi2ÀxO3:Smx (x ¼ 1e11 mol%) NPs excited at 365 nm and 465 nm The CIE colour coordinates so calculated for Bi2ÀxO3:Smx (x ¼ 1e11 mol%) are summarized in Fig 7(a) It is clear that all the 536 S Ashwini et al / Journal of Science: Advanced Materials and Devices (2019) 531e537 samples fall into the scope of orange red light emission Fig 7(b) shows CCT of Bi2ÀxO3:Smx (x ¼ 1e11 mol%) and the average value was found to be 1758 K [41] Hence, it is obvious that the NPs can be used as an Orange red light source to meet the needs of the illustrated applications maximum for mol% (Fig 10) This might be due to the fact that at mol%, Sm3ỵ ions on the host Bi2O3 behave as electron trapper to detach the electronehole pairs which is much needed for PCA At other molar concentrations, the catalyst may behave as recombination centres and this leads to less PCA efficiency 3.6 Photocatalytic activity of AR-88 dye Conclusion Acid Red-88 (AR-88) is an azo dye Due to its intense colour, Ar88 was used to dye cotton textiles red and used for Photocatalytic studies The PCA of Bi2ÀxO3:Smx (x ¼ 1e11 mol%) were analysed for the decolourization of AR-88 in aqueous solution under UV light irradiation for a time duration of 60 The UV visible absorption spectra of the dye for various concentrations of Bi2ÀxO3:Smx (x ¼ 1e11 mol%) are shown in Fig 8(aef) To know about the response kinetics of AR-88 Dye decolourization, the LangmuireHinshelwood model was adopted which follows the equation, ln (C/C0) ẳ kt ỵ a, where, k is the reaction rate constant, C0 the preliminary attention of AR-88, C the attention of AR-88 on the response time t [22,42] Fig shows the plot of ln (C/C0) photo decolourization of all catalysts Bi2O3:Sm3ỵ under UV light irradiation As the doping concentration increases, the photo decolourization efficiency decreases and after 60 irradiation it was found that the photo decolourization efficiency was 98.57% which is the The present Bi2O3:Sm3ỵ nanophosphors were prepared by a solution combustion method The crystallite size was found to be in the range 13e30 nm The phosphors upon exciting at comparably low energy of 465 nm, emit orange colour with all 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photoluminescence properties of a novel Sr2CeO4:Dy3ỵnanophosphor with enhanced brightness by Liỵ codoping, RSC Adv (2014) 38655e38662 [42] C Pratapkumar, S.C Prashantha, H Nagabhushana, M.R Anilkumar, C.R Ravikumar, H.P Nagaswarupa, D.M Jnaneshwara, White light emitting magnesium aluminate nanophosphor: near ultra violet excited photoluminescence, photometric characteristics and its UV photocatalytic activity, J Alloys Compd 728 (2017) 1124e1138 ... shows an excellent photocatalytic activity which proofs the multi functionality of the prepared nanophosphors Bi2O3: Sm1 mol % 0.0 Bi2O3: Sm3 mol % Bi2O3: Sm5 mol % Bi2O3: Sm7 mol % Bi2O3: Sm9 mol... (1e11 mol%) doped Bi2O3 NPs Table Crystallite size of Bi2O3: Sm3ỵ Sl no Compound Bi2O3: Sm3ỵ: Bi2O3: Sm3ỵ: Bi2O3: Sm3ỵ: Bi2O3: Sm3ỵ: Bi2O3: Sm3ỵ: Bi2O3: Sm3ỵ: Crystallite size (nm) mol% mol% mol% mol%... view of its low temperature and reduced time consumption which result in a high degree of crystallinity and homogeneity The synthesised nanophosphor is characterized by PXRD and DRS The effect of