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Novel crystalline tetragonal ZrO 2 : Eu 3+ phosphors were prepared by a facile and efficient low temperature solution combustion method at 400 ± 10 °C using oxalyl dihydrazide (ODH) as fuel. The powder X-ray diffraction patterns and Rietveld confinement of as formed ZrO 2 : Eu 3+ (1–11 mol%) confirmed the presence of body centered tetragonal phase. The crystallite size estimated from Scherrer’s and W–H plots was found to be in the range of 7–17 nm. These results were in good agreement with transmission electron microscopy studies. The calculated microstrain in most of the planes indicated the presence of tensile stress along various planes of the particles. The observed space group ( P4 2 /nmc ) revealed the presence of cations in the 2b positions (0.75, 0.25, 0.25) and the anions in the 4d positions (0.25, 0.25, 0.45). The optical band gap energies estimated from Wood and Tauc’s relation was found to be in the range 4.3–4.7 eV. Photoluminescence (PL) emission was recorded under 394 and 464 nm excitation shows an intense emission peak at 605 nm along with other emission peaks at 537, 592, 605 and 713 nm. These emission peaks were attributed to the transition of 5 D 0 → 7 F J ( J = 0, 1, 2, 3) of Eu 3+ ions. The high ratio of Intensity of ( 5 D 0 → 7 F 2 ) and ( 5 D 0 → 7 F 1 ) infers that Eu 3+ occupies sites with a low symmetry and without an inversion center. CIE color coordinates indicated the red regions which could meet the needs of illumination devices. [ABSTRACT FROM AUTHOR]

Eco-friendly, cost effective and bio template route was used for the preparation of cubic Gd 2 O 3 :Eu 3+ nanophosphors using Euphorbia tirucalli ( E. tirucalli ) plant latex as fuel. As – formed Gd 2 O 3 :Eu 3+ (7 mol%, 1–7 ml), calcined Gd 2 O 3 :Eu 3+ (7 mol%, 1–7 ml) and Gd 2 O 3 :Eu 3+ (1–11 mol%, 7 ml) samples were characterized using XRD, SEM and UV–Vis absorption spectrophotometer. With increase in latex concentration, the nanophosphor gets transformed from nano plates to rose – like nanoflowers with size varying from 20 to 30 nm. X-ray diffraction pattern of as – formed product shows hexagonal Gd (OH) 3 : Eu 3+ phase and it converts to pure cubic phase of Gd 2 O 3 :Eu 3+ on calcination at 600 °C for 3 h. Rietveld refinement of Gd 2 O 3 :Eu 3+ (7 mol%, 7 ml) revealed the presence of cations in the 8 b (0.25, 0.25, 0. 25) and 24 d positions (−0.0287, 0.00, 0. 25) and the anions in the 48 e positions (0.39, 0.15, 0. 37) with space group Ia -3(206). The photoluminescence intensities of transitions between different J levels depend on the symmetry of the local environment of Eu 3+ ion activators and the high ratio of intensity of ( 5 D 0 → 7 F 2 ) and ( 5 D 0 → 7 F 1 ) provides the conclusion that Eu 3+ ion occupies sites with a low symmetry and without an inversion centre. The chromaticity and the CIE coordinates were very close to the standard red color region. The absorption observed in the excitation spectra shows the suitability of the nanophosphor obtained in this study for getting excited in UV, NUV and visible regions for variety of display applications. Further, the Gd 2 O 3 :Eu 3+ (7 mol%, 1–7 ml) samples were experimented towards the photocatalytic behavior on Congo red (CR) and correlated with emission of PL intensity. The decolorization of dye was found to decreased from 83 to 54% with increase in the plant latex concentration. [ABSTRACT FROM AUTHOR]

LaAlO 3 :Dy 3+ (1–11 mol%) nanophosphors (NPs) were synthesized using solution combustion route and the final product was well characterized. The bandgap energy (E g ) was estimated using diffuse reflection data and the value was found to be in the range 5.70 – 5.90 eV. Upon ~ 353 nm [ 6 H 15/2 → 6 P 5/2 ] excitation, a characteristic emissions peaks of Dy 3+ ions were recorded at ~ 480, 576 and 673 nm and ascribed to transitions from 4 F 9/2 to 6 H 15/2, 6 H 13/2 and 6 H 11/2 respectively. Judd–Ofelt parameters (Ω 2 , Ω 4 and Ω 6 ), transition probabilities (A T ), quantum efficiency (η), luminescence lifetime (τ rad ), branching ratio (β), color chromaticity coordinates (CIE) and correlated color temperature (CCT) values were estimated from the emission spectra and discussed in detail. The estimated branching ratio was found to be ∼75%, as a result the phosphor may be potentially useful for display device applications. Further, the optimized LaAlO 3 :Dy 3+ (5 mol%) nanophosphor can be effectively used in the white light emitting diodes (WLEDs) under NUV excitation. [ABSTRACT FROM AUTHOR]

Sm 3+ doped (1–9 mol%) Lanthanum aluminate (LaAlO 3 ) nanophosphor was prepared by solution combustion synthesis and characterized by photoluminescence (PL), powder X-ray diffraction (PXRD), UV–vis (UV-vis), scanning and transmission electron microscopy (SEM and TEM). PL excitation and emission spectra, quantum efficiency, luminescence life time were studied to investigate the luminescence properties of LaAlO 3 :Sm 3+ nanophosphor, effectively excited by near UV wavelength 406 nm. The combination of different coloured emissions in visible region presents a desired white light which leads to the WLED application. The chromaticity coordinates of the optimized concentration of Sm 3+ was estimated to be (0.3684, 0.4066) and the corresponding correlated color temperature (CCT) was found to be ∼4485 K which favors in warm white light emissive display applications. The luminescence quantum efficiency was calculated from the emission spectra using Judd–Ofelt (J-O) theory. From the analysis the estimated branching ratio (∼56%) was greater than 50%, as a result the phosphor was highly suitable for display devices. The present phosphor was highly useful as thermal sensor in the temperature interval between 100 to 400 °C as estimated from decay time measurements. [ABSTRACT FROM AUTHOR]

A series of Eu 3+ (1–7 mol %) doped Y 2 SiO 5 red nanophosphors were prepared by eco-friendly combustion route using Calotropis gigantea latex as a fuel. The obtained nanophosphors were calcined at 1000 °C and characterized by powder X-ray diffraction (PXRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier-transform infrared spectroscopy (FTIR), Raman studies, UV–Visible and photoluminescence (PL) spectroscopic techniques. PXRD were used to determine the structure of the phosphors, showing that the product was monoclinic phase of X1 type Y 2 SiO 5 having a phase group P2 1/c n. 14. The PL properties of samples exhibited an intense broad red emission band upon excitation with 397 nm, with a peak at 612 nm, color coordinates of (0.5866, 0.4026), and average correlated color temperature ~2018.5 K. Based on Judd–Ofelt (J–O) theory, the intensity parameters ( Ω 2 and Ω 4 ) were evaluated from the emission spectra of Y 2 SiO 5 : Eu 3+ (1–7 mol %) nanophosphors. The registered trend ( Ω 2 < Ω 4 ) reveals the relatively high symmetry environment around the rare earth ion (RE) site in Y 2 SiO 5 as compared to other host matrix. The results show that prepared samples were compared with the commercially available compound and founds as par to the commercial compound hence it may be used as a potential red phosphors for near UV excited White LEDs applications. [ABSTRACT FROM AUTHOR]

Green combustion synthesis using Calotropis gigantea latex as fuel, NaCl as flux were employed for the synthesis of Y 2 SiO 5 :Ce 3+ (1 mol%):Sm 3+ (0.2–1 mol%) nanoparticles. The 1000 °C calcined phosphors were characterized by powder X-ray diffraction (PXRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The powder X-ray diffraction (PXRD) patterns of the sample revealed a monoclinic phase with space group P 21/ C (n.14). The crystallite size using Scherer's formula and W–H plot was found to be in the range 34–39 nm and the same was confirmed by transmission electron microscopy (TEM) studies. Scanning electron microscopy (SEM) pictures show porous with agglomerated crystallites. The effect of Sm 3+ ions on the luminescence characteristics of Y 2 SiO 5 :Ce 3+ nanoparticles was studied and the results were discussed in detail. The phosphors exhibit bright orange red emission upon 404 nm excitation. The emission spectra consists of sharp emission peaks at 566, 601 and 654 nm which were attributed to typical 4 G 5/2 → 6 H 5/2 , 4 G 5/2 → 6 H 7/2 and 4 G 5/2 → 6 H 9/2 transitions of Sm 3+ ions, respectively. The Commission International de I’Eclairage (CIE) chromaticity co-ordinates were estimated from emission spectra which falls in white region of the CIE spectra. Further, color correlated temperature (CCT) was found to be 5011 K. Hence, the present phosphor was highly useful for mercury free solid state lighting (SSL) and also for white display applications. [ABSTRACT FROM AUTHOR]

Dy 3+ doped Mg 2 SiO 4 nanoparticles have been synthesized by the solution combustion method at 350 °C temperature. The crystallinity and changes of lattice parameters with the incorporation of the Dy 3+ ions are studied by means of Powder X-Ray Diffraction studies. Fourier transform infrared data indicate the formation of bonds and capping of the nanoparticles. Scanning electron microscopy pictures evident for the product is porous and agglomerated. The nano size of the product is confirmed by means of transmission electron microscopy. The characteristic emission peaks and the Judd–Ofelt intensity parameters of Mg 2 SiO 4 :Dy 3+ nanoparticles are studied. The emission can be tuned from green (0.238, 0.348) to white (0.276, 0.347) which indicates, the prepared phosphors can be effectively used for white light emitting diodes and biosensors. Further, the degradation of dyes is found to be enhancing in the presence of Dy 3+ ions due to suppress of the e − CB and h + VB recombination. [ABSTRACT FROM AUTHOR]

This work explores the synthesis of nanocrystalline MgO:Cr 3+ (1–9 mol%) nanophosphors via solution combustion route at 400 °C. The nanophosphors were well characterized by powder X-ray diffraction (PXRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and Fourier transform infra-Red (FTIR) spectroscopy. PXRD results confirm cubic phase and SEM micrographs indicate that the particles are highly porous and agglomerated. The TEM images show that the powder consists of spherical particles of size ∼5–15 nm. Upon 356 nm excitation the emission profile of MgO:Cr 3+ exhibits an emission peak at 677 nm due to 2 E g → 4 A 2g transition. It was observed that PL intensity increases with increase in Cr 3+ concentration and highest PL intensity was observed for 3 mol% doped sample and afterward it decreases, attributed to concentration quenching. The resultant CIE chromaticity co-ordinates in the white region make the present phosphor highly useful for display applications and also for white light-emitting diodes (WLEDs). [ABSTRACT FROM AUTHOR]

Ho 3+ (0.25–7 mol%) doped Sr 2 CeO 4 nanophosphors were synthesized by solution combustion method using urea as fuel. The structural properties of the nanophosphors were investigated by powder X-ray diffraction studies (PXRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) techniques. UV–Visible and photoluminescence (PL) spectroscopic techniques were used for analysing the optical properties of the nanoparticles. PXRD and TEM results revealed the formation of Sr 2 CeO 4 : Ho 3+ nanocrystalline particles with orthorhombic crystal structure. From the UV–Vis studies the optical band gap energy found to decrease from 5.9 to 5.74 eV with increase in dopant concentration. The PL spectra exhibit the broad excitation band from 200 to 400 nm which concurs well with the commercial near UV LED. The PL spectra vary with the dopant content due to energy transfer from the host to the activator. In this present work we demonstrate that color tuning of phosphor can be achieved by merely varying the Ho 3+ ions concentration. The CIE and CCT chromaticity coordinates suggests Sr 2 CeO 4 : Ho 3+ nanophosphors may be potentially applicable as promising single – phased phosphors for lighting applications. [ABSTRACT FROM AUTHOR]

Europium doped lanthanum aluminate nanophosphors were synthesized by a combustion process using Oxalyl di-hydrazide as fuel. The nanophosphors calcined at 900 °C for 3 h were characterized by PXRD, FTIR spectroscopy, SEM and TEM. The average crystallite size determined by TEM and Scherrer's method was found to be in the range 20–50 nm. The characteristic emission peaks (λ exi - 395 nm) recorded at ∼ 591, 616, 646 and 696 nm ( 5 D 0 → 7 F j=0,1,2,3 ) may be attributed to the 4f–4f intra shell transitions of Eu 3+ ions. The estimated CIE chromaticity co-ordinates were calculated from emission spectra, were close to the national television standard committee value of red emission. Correlated color temperature was found to be 1929 K. [ABSTRACT FROM AUTHOR]

Facile and green route was employed for the synthesis of Y 2 O 3 :Dy 3+ (1–11 mol%) nanostructures (NSs) using Aloe vera gel as fuel. The formation of different morphologies of Y 2 O 3 :Dy 3+ NSs were characterized by SEM, TEM and HRTEM. PXRD data and Rietveld analysis evident the formation of single phase Y 2 O 3 with cubic crystal structure. The influence of Dy 3+ ion concentration on the structure morphology, UV absorption, PL emission and photocatalytic activity of NSs were investigated. NSs exhibited an intense warm white emission with CIE chromaticity coordinates (0.32, 0.33) and average CCT value ∼5525 K which corresponds to vertical day light. The control of Dy 3+ ion on Y 2 O 3 matrix influences the photocatalytic decolorization of Metanil Yellow as a model compound was evaluated. The enhanced photocatalytic activities of core shell structured Y 2 O 3 :Dy 3+ (1 mol%) was attributed to co-operation effect of dopant concentration, crystallite size, textural properties and capability for reducing electron–hole pair recombination. Further, the recycling catalytic ability of Y 2 O 3 :Dy 3+ (1 mol%) nanostructure was also evaluated and found promising photocatalytic performance with negligible decrease in decolorization efficiency even after sixth successive cyclic runs. Considering its green, facile synthesis and recyclable feature from an aqueous solution, the present Y 2 O 3 :Dy 3+ (1 mol%) nanophosphor can be considered as one of the ideal photocatalyst for various potential applications. [ABSTRACT FROM AUTHOR]

We report the synthesis of Y 2 O 3 : Eu 3+ (1–11 mol%) nanoparticles (NPs) with different morphologies via eco-friendly, inexpensive and simple low temperature solution combustion method using Aloe Vera gel as fuel. The formation of different morphologies of Y 2 O 3 : Eu 3+ NPs were characterized by PXRD, SEM, TEM, HRTEM, UV–Visible and PL techniques. The PXRD data and Rietveld analysis confirms the formation of single phase Y 2 O 3 with cubic crystal structure. The influence of Eu 3+ ion concentration on the morphology, UV–Visible absorption, PL emission and photocatalytic activity of Y 2 O 3 : Eu 3+ nanostructures were investigated. Y 2 O 3 : Eu 3+ NPs exhibit intense red emission with CIE chromaticity coordinates (0.50, 0.47) and correlated color temperature values at different excitation ranges from 1868 to 2600 K. The control of Eu 3+ ion on Y 2 O 3 matrix influences the photocatalytic decolorization of methylene blue (MB) as a model compound was evaluated under UVA light. Enhanced photocatalytic activity of conical shaped Y 2 O 3 : Eu 3+ (1 mol%) was attributed to dopant concentration, crystallite size, textural properties and capability of reducing the electron–hole pair recombination. The trend of inhibitory effect in the presence of different radical scavengers followed the order SO 4 2− > Cl − > C 2 H 5 OH > HCO 3 − > CO 3 2− . These findings show great promise of Y 2 O 3 : Eu 3+ NPs as a red phosphor in warm white LEDs as well as eco-friendly heterogeneous photocatalysis. [ABSTRACT FROM AUTHOR]

The current study involves synthesis of a series of Tb 3+ doped ZrO 2 nanophosphors by solution combustion method using oxalyl dihydrazide as fuel. The as-formed ZrO 2 :Tb 3+ nanophosphors having different concentrations of Tb 3+ (1–11 mol%) were characterized by powder X-ray diffraction (PXRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and UV–Visible spectroscopic techniques and the materials were subjected to photoluminescence and photocatalytic dye decolorization studies. The PXRD analysis indicates the formation of tetragonal symmetry up to 5 mol% concentration of Tb 3+ . Further increase in Tb 3+ concentration has lead to cubic phase formation and the same was confirmed by Rietveld refinement analysis. SEM images revealed that material was highly porous in nature comprising of large voids and cracks with irregular morphology. TEM and SAED images clearly confirm the formation of high quality tetragonal nanocrystals. The emissive properties of nanophosphors were found to be dependent on Tb 3+ dopant concentration. The green emission of the material was turned to white emission with the increase of Tb 3+ ion concentration. The photocatalytic activities of these nanophosphors were probed for the decolorization of Congo red under UV and Sunlight irradiation. All the photocatalysts showed enhanced activity under UV light compared to Sunlight. The photocatalyst with 7 mol% Tb 3+ showed enhanced activity attributed to effective separation of charge carriers due to phase transformation from tetragonal to cubic. The influence of crystallite size and PL on charge carrier trapping–recombination dynamics was investigated. The study successfully demonstrates synthesis of tetragonal and cubic ZrO 2 :Tb 3+ green nanophosphors with superior photoluminescence and photocatalytic activities. [ABSTRACT FROM AUTHOR]

ZnAl 2 O 4 :Cr 3+ nanophosphors were synthesized for the first time by a simple and environment friendly route using Calotropis procera milk latex as fuel. The structural and surface morphological studies were carried out using powder X-ray diffraction (PXRD), scanning electron microscopy and transmission electron microscopy techniques. The photoluminescence (PL) properties of ZnAl 2 O 4 :Cr 3+ as a function of dopant concentration and calcination temperature was studied in detail. The PXRD patterns and Rietveld confinement confirmed the cubic crystal system with space group Fd - 3m . The crystallite size estimated from Scherrer’s and W–H plots was found to be in the range of 16–26 nm. The PL spectrum shows an intense peak at ∼688 and ∼699 nm assigned to spin – forbidden 2 E g → 4 A 2g transition of Cr 3+ ions. The PL measurements for two excitations (∼410 and 527 nm) and with respect to calcination temperature indicated no significant change in the shape and position of emission peak except PL intensity. The CIE chromaticity coordinates lies well within the white region. Thermoluminescence (TL) studies revealed well resolved glow peak at ∼212 °C with a small shoulder at 188 and 233 °C. The glow peak intensity at ∼212 °C increases linearly with γ-dose which suggest ZnAl 2 O 4 :Cr 3+ is suitable candidate for radiation dosimetric applications. The activation energy ( E in eV), order of kinetics ( b ) and Frequency factor ( s ) were estimated using glow peak shape method. [ABSTRACT FROM AUTHOR]

For the first time nanoparticles of Tb 3+ doped (1–11 mol%) Mg 2 SiO 4 have been prepared using low temperature (350 °C) solution combustion technique with magnesium nitrate as precursor and oxalyl di-hydrazide (ODH) as fuel. The Powder X-ray diffraction (PXRD) patterns of the sample revealed orthorhombic structure with α-phase. The average crystallite size using Scherer’s formula, W – H plot and Size–strain plot is found to be 28 nm and the same is confirmed by Transmission electron microscopy (TEM) studies. Scanning electron microscopy (SEM) pictures show a porous structure and the crystallites were agglomerated. The effect of Tb 3+ cations on luminescence characteristics of Mg 2 SiO 4 is studied and the results are discussed in detail. The phosphors exhibit bright green emission upon near ultra violet (NUV) 377 nm excitation. The characteristic photoluminescence emission peaks at 417, 436, 458 nm in blue region due to 5 D 3 → 7 F J ( J = 5, 4, 3) of Tb 3+ ions and the emission peaks at 486, 541, 584 and 621 nm in green region corresponds to 5 D 4 → 7 F J ( J = 6, 5, 4, 3) transitions of Tb 3+ ions owing to f–f transitions of Tb 3+ cations in the given host lattice and are due to dipole–quadropole interactions. The CIE chromaticity co-ordinates are calculated from emission spectra and falls in green region. Therefore the present phosphor is highly useful for mercury free solid state lighting (SSL) and also for display applications. [ABSTRACT FROM AUTHOR]