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In this review article, a brief discussion of fluoroquinolones (FQs) and their tendency to form metal complexes is presented. The effect of FQs-M complexes on disease causing microorganisms is also summarized. The antibacterial activity of various metal complexes of various fluoroquinolones [norfloxacin (NOR), ciprofloxacin (CIP), levofloxacin (LEVO), ofloxacin (OFL), gemifloxacin (GEMI), gatifloxacin (GATI), moxifloxacin (MOX), enrofloxacin (ENRO), sparfloxacin (SPRX)] is reviewed by comparing zone of inhibition and MIC values of metal complexes. It is found to be either corresponding with the parent fluoroquinolone or in some cases their respective metal complexes exhibit stronger antibacterial activity. New approach towards synthesis of FQ-metal complexes has led to formation of compounds with the anticancer and antiviral activity.

An energy efficient solution combustion technique was selected for fabricating a series of energy-efficient novel down-converted Ba3Y4O9:Er3+ nanoparticles with green emission. Crystal structure engineering along with the morphological aspects was investigated via certain advanced characterizations such as Rietveld refinement and powder X-ray diffractometry (PXRD) procedure, microscopic practices like scanning and transmission electron microscope techniques, photoluminescence and diffuse reflectance spectroscopic analysis. Average crystallite size (65.71 nm–74.15 nm) and micro strain (0.0012) of the optimum powder nanomaterial were analyzed from high quality XRD data using Williamson-Hall (W–H) plot method. Alluring spectroscopic features were realized by photoluminescent (PL) spectra recorded upon excitation via near ultraviolet (NUV) source of 381 nm; displaying an intense emission peak (562 nm) situated in the visible region that is solely responsible for the green glow of the prepared phosphor. PL analysis witnessed a bright green emission via a reliable emanation transition (4S3/2 → 4I15/2) of Er3+ ions. Excellent colorimetric parameters of optimized nanophosphor like CIE coordinates (0.3420, 0.6064), 5356K CCT and 79.02% color purity validated its advanced photonic and optoelectronic applications for cool light emitting WLEDs, lasers, optical sensors, solar and photovoltaic cells.

The present prospective observational study reports the generation of new Sm3+-incorporated BaYAlZn3O7 nanomaterials via urea-combustion route. Rietveld facilitated XRPD (X-ray powder diffraction) analysis outlines the absolute hexagonal phase in the nano-crystalline powders. Photo-luminescence (PL) technique reports the intense-orange–red emission, centered at 708 nm maximum. Higher content of Sm3+ retards the PL life-time and intensity, such that x = 0.02 is the best luminance composition. Post it, luminance quenching has been ascertained, which is attributed to the exchange type inter-linkages, as affirmed via Inokuti–Hirayama and Dexter’s model. Also, various radiative-possessions including decay-time (2.4876 ± 0.0311 ms), intrinsic life-time (3.4380 ms), quantum-efficiency (72.36%) and relaxation-rate (0.1111 ms−1), which reflect their better luminance-potentiality, have been evaluated. Color-coordinates (0.5299, 0.4670) for the same phosphor have realized their intense-orange radiance, which are proximate to those (0.570, 0.420) illustrated via AMBER LED-NSPAR 70 BS (generated via NICHIA CORP.). All the crystallographic and optical properties of the phosphor-powders, thus, vividly define their potential usage in near-ultra-violet triggered white-light-emitting diodes, digital-signs, horticulture, bio-imaging, solar-cells, lasers, and other optoelectronic appliances. Also, all the reported outcomes will certainly open an avenue for researchers to design more BaYAlZn3O7-like materials.

A series of green light-emitting Ba5Zn4Y8O21:Er3+ nanophosphors were prepared via single-step solution combustion process. PXRD-Rietveld investigation revealed that Er3+ ions are well-substituted Y3+ ions and no major change was observed in the crystalline structure of pure host matrix. Tetragonal nanoparticles with almost no agglomeration were revealed by morphological analysis. Different elements present in the prepared nanomaterials were elucidated via EDAX mapping. Photoluminescence investigation of Ba5Zn4Y8O21:Er3+ nanophosphors displayed an intense green emission peak of Er3+ ions credited to 4S3/2 → 4I15/2 transition, under NUV excitation of 379 nm. The concentration quenching occurred after 2.0 mol% concentration of the Er3+ ions in Ba5Zn4Y8O21 host, thus apprehended it an optimized concentration. CIE coordinates (x, y) of all the prepared nanocrystalline phosphors lied in the green region. Bandgap (Egap) values of the optimized sample were calculated by analysing the DR spectra of that sample which are found to be 4.0 eV for the pure host and 3.9 eV for the doped sample which lie in semiconductor range. The brief description of all these results proves the importance of synthesized nanophosphors in R-G-B (red–green–blue) PC white light-emitting diodes (WLEDs).

A bright orange-red emanating Ca9Bi1−x(VO4)7:xSm3+ (x = 0.05–0.5) nanophosphor crystalline series has been synthesized for the first time through solution combustion route. X-ray diffraction pattern of Ca9Bi0.80Sm0.20(VO4)7 was analyzed and processed using Rietveld Refinement. The nanophosphors synthesized were found to crystallize in trigonal crystal lattice with R3c(161) space group. The morphological behavior of prepared nanophosphors was studied by means of transmission electron microscopy (TEM). The photoluminescence nature of the nanophosphors corresponds to bright orange emission due to near-ultraviolet (NUV) excitation at 405 nm followed by 4G5/2 → 6H7/2 radiative relaxation. The chromaticity coordinates (x = 0.5504, y = 0.4484) are in harmony with the intense orange-red emission. The decay curves been well fitted in 1st-order exponential decay function indicate that a single type of crystallographic site is occupied by the dopant-Sm3+ ions in host lattice. Auzel’s model was implemented to investigate into rates of nonradiative relaxation (302.008 s−1), radiative lifetime (0.76 ms), and quantum efficiency (81%) values. The crystalline and optical behavior of the synthesized orange-red emitting nanophosphors promote their usage in near UV-based WLEDS.

A series of five virescent color emitting terbium(III) complexes is fabricated by a cost-effective and eco-friendly solution precipitation technique with the utilization of 1-(4-methoxyphenyl)-5-(trifluoromethyl)-1H-pyrazole-4-carboxylic acid (L) as a primary ligand and highly conjugated nitrogen donor secondary ligands such as bathophenanthroline (batho), 5,6-dimethyl-1,10-phenanthroline (dmph), 1,10-phenanthroline (phen) and 2,2-bipyridyl (bipy). The elemental compositions of complexes are examined through energy dispersive x-ray and elemental analyses, whilst the binding nature of ligand with terbium(III) ion is confirmed using proton nuclear magnetic resonance and infrared spectroscopy. The band gap energy (Eg) of complexes is found in the range of 3.85–3.34 eV as evaluated from diffuse reflectance spectral data. The significant thermal stability of these luminescent materials (157°C) demonstrates their key role as virescent component in white organic light emitting diodes. The intense emission and decay time of complexes are explored through photoluminescent study. The good color purity and Commission International De I’Eclairage color coordinates promise the enhanced performance of these materials in lighting appliances. The sensitization phenomenon highlights the role of ligands in increasing the luminescence intensity of complexes. The biological assessment indicates that the complexes are potent antimicrobial and antioxidant agents. The aforementioned features extend the field of applications of complexes in laser technology and optoelectronic devices.

Novel cubic perovskite based orange red emissive Sr9(1-x)Al6O18: 9xSm3+ (0.001 ≤ x ≥ 0.04) nanocrystals were developed by environmentally benign and low temperature urea combustion method. Phase structure analysis showed the cubic structure with Pa 3 ‾ ( 205 ) space group. Scanning and transmission electron micrographs reported the agglomerated cubic morphology of the nanoparticles ranging from 40 to 60 nm. EDS (energy dispersive X-ray analysis) outcomes traced the adequate elemental composition of the spectral materials. The prepared nanomaterials displayed the fine orange red emission via 4G5/2 → 6H7/2 typical transition centered at 599 nm. Optical analysis asserted the wide band gap values of Sr8.82Sm0.18Al6O18 (3.77 eV) and Sr9Al6O18 (4.08 eV). Reliance of the emission intensity of developed nanophosphors on Sm3+ concentration claimed the Sr8.82Sm0.18Al6O18 as most desirable one with CIE coordinates (0.5833, 0.4159), 1747 K correlated color temperature (CCT) and color purity of 90.65%. These excellent results proved the relevancy of present nanophosphors as a novel promising material in the development of down conversion white LEDs. Also, the present research findings thus, can be well recurred to explore more about Sr9Al6O18 based spectral nanomaterials.

Four red photoluminescent europium(III) complexes have been synthesized by using fluorinated carboxylate ligand, 1-(4-methoxyphenyl)-5-(trifluoromethyl)-1H-pyrazole-4-carboxylic acid as main ligand...

To solve the problem of multiphased commercial light emitting diodes, a series of new single-phased BaLaAlO4:Dy3+ nanophosphors emitting cool white light were successfully fabricated via an energy-...

To improve the current multi-phased white-LEDs, novel down-converted Dy3+ doped layered perovskite SrLaAlO4 nanophosphors emitting cool white light were successfully fabricated by urea assisted solution combustion approach. X-ray diffractometry and Rietveld refinement revealed the 14/mmm (139) space group of tetragonal phase in doped samples (SrLa(1-x)DyxAlO4 (x = 0.01–0.10)). Morphological studies reported the nanocubic crystals (45–55 nm) while their nanocrystalline nature and (101) crystal plane was depicted by selected area electron diffraction patterns. Elemental composition of nanomaterials was detected effectively via energy dispersive X-ray analysis. The vibrational metal-oxygen bonding in the sample was confirmed by FT-IR results. Photoluminescence spectra, on near UV excitation, showed two intense bands of blue and yellow color at 484 and 574 nm subjected to transition from 4F9/2 → 6H15/2 and 6H13/2, respectively. Maximum emission intensity was noticed for 5.0 mol% amount of dopant (Dy3+) ions. Decay life time, band gap and refractive index of optimized sample were noted as 0.413 ms, 4.98 eV and 1.736, respectively. CCT value (7418 K), color purity (23.02 × 10−2) and CIE coordinates (0.308, 0.284) of SrLa0.95Dy0.05AlO4 nanophosphor were approximate to coordinates of commercial LEDs and National Television System Committee, which confirmed their excellent practicability in the advanced optoelectronic devices, especially single-phase WLEDs for the illumination purpose.

Five luminescent europium (III) carboxylate complexes have been synthesized by using ligand 3-isopropylpyrazole-5-carboxylic acid as primary ligand and 4,4’-dimethyl-2,2’-bipyridyl, 2,2’-bipyridyl, 5,6-dimethyl-1,10-phenanthroline and 1,10-phenanthroline as secondary ligands and characterized through various techniques. These complexes exhibit excellent thermal stability and characteristic europium centered photoemission spectra under the excitation of ultraviolet light. Luminescence decay curves, Judd–Ofelt analysis, internal quantum efficiency and energy transfer mechanism have also been discussed. The color coordinates and color purity are calculated to investigate red emission of the complexes. The study results reveal that these complexes can be potentially used as red light emitting materials in various optoelectronic devices.

Unique down-conversion virescent SrLaAlO4:Er3+ nanocrystals were successfully fabricated by urea-assisted solution combustion route. Presence of tetragonal phase in doped samples [SrLa(1−x)ErxAlO4 (x = 0.1–4.0 mol%)] with a space group of 14/mmm (139) was investigated by powder X-ray diffractometry and Rietveld refinement analysis. Nanocubic crystals with their size ranging from 45 to 55 nm were displayed by scanning electron microscopy and transmission electron microscopy (TEM) techniques while high-resolution TEM highlighted the (105) crystallite plane by representing the resolved fringes of lattice. Nanocrystalline nature and the (101) crystal plane was depicted by selected area electron diffraction patterns of the powder sample. Qualitative as well as quantitative elemental composition of nanophosphors were investigated by mapping and spectra of energy dispersive X-ray analysis, respectively. On near UV excitation, photoluminescence emission spectra showed a prominent band of green color due to 4S3/2 → 4I15/2 transition (549 nm). Energy bandgap and refractive index of optimized sample were determined as 4.97 eV and 1.736, respectively, via diffuse reflectance spectra. Color chromaticity coordinates (0.1735, 0.6909) of SrLa0.98Er0.02AlO4 nanophosphors verified their virescent emission with a color purity of 100% and were found to be consistent with the standard values of European Broadcasting Unit (EBU) as well as International Telecommunication Union, thus reflected their important role as the green component in the solid-state lighting devices, especially red–green–blue pc-white light-emitting diodes.

Nano-scaled green-emitting Ba3Bi2(PO4)4:Tb3+ crystalline series was effectively obtained via very efficient and straightforward combustion-synthesis route for the very first time. The JCPDS data (Card No: 780204) of Ba3Bi2(PO4)4 crystal were used for profiling the diffraction patterns of various mol% samples. The structure and lattice parameters of Ba3Bi1.70Tb0.30(PO4)4 system have been investigated by Rietveld refinement analysis. Further, it was found that incorporation of dopant (Tb3+) ion into the monoclinic crystal lattice of C12/c1 (15) space group symmetry did not induce any major structural changes. Lowering in the optical band-gap value from 4.16 to 4.02 eV was observed when Ba3Bi2(PO4)4 host lattice is doped with 15 mol% of activator ions. The photoluminescence analysis of Ba3Bi2(PO4)4:Tb3+ series at 368 nm excitation yielded the bright green emission due to the 5D4 → 7F5 transition. A maximum in emission intensity is observed corresponding to the Ba3Bi1.70Tb0.30(PO4)4 composition. Critical energy distance (13.235 A) proposed the existence of energy transfer through multipolar interaction (dipole–dipole) phenomenon, which is cross-verified by Huang analysis (s = 4.94). The value of radiative-lifetime and non-radiative transition rate are calculated to be 2.22 ms and 10.3 s−1, respectively. Furthermore, the very high value of quantum efficiency (97%) and the results of various optical analysis favor the practical utility of down-conversion Ba3Bi1.70Tb0.30(PO4)4 nanophosphor for solid-state and other illuminating devices.

Novel down-conversion SrGdAlO4:Er3+ nanophosphors with emerald emission were synthesized efficiently with a great success through solution combustion technique. Characterizations regarding crystallographic studies and morphological attributes were practiced by the powder XRD, EDX, SEM and TEM. Refined atomic parameters and positions were calculated for optimal sample SrGd0.96Er0.04AlO4 by realizing Refinement technique. The outcomes revealed the tetragonal phase of the doped lattice with 14/mmm (139) space group and particle size of 49.5 nm. EDX confirmed the chemical composition of sample while SEM and TEM images showed the spherical shape of nano particles with their size in the range of 49–55 nm whereas the distance between fringes present in the nanosamples was calculated as 0.204 nm by HRTEM image. FT-IR spectroscopy indicated the presence of stretching vibrations of Al–O bonds in the aluminate type of host lattice by exhibiting sharp peaks at 1154 and 1074 cm−1. Photoluminescence properties were investigated by recording photoluminescence (PL) excitation and emission, decay curves and diffuse reflectance (DR) spectra. The doped nanophosphor displays the exclusive emerald emission peaks of Er3+ ion subjected to 4S3/2 → 4I15/2 transition and its optimal concentration was remarked as 4.0 mol%. The value of critical distance (Rc) came out to be 15.91 A which induced both the dipole-dipole and electric dipole-quadrupole interrelations as the possible mechanism for concentration quenching. The detailed description of decay curves depicted the value of life time (0.29 ms) for optimized nanophosphor. DRS specified the band gap (Eg) values for SrGdAlO4 (5.50 eV) as well as SrGd0.96Er0.04AlO4 (5.47 eV). CIE coordinates confirmed the emerald emission of novel and energy efficient Er3+ doped nanophosphors which proclaims their potential uses in the PC-WLEDs as well as other opto-electronic devices.

Six crimson samarium (III) complexes based on β-ketone carboxylic acid and ancillary ligands were synthesized by adopting grinding technique. All synthesized complexes were investigated via employing elemental analysis, infrared, UV-Vis, NMR, TG/DTG and photoluminescence studies. Optical properties of these photostimulated samarium (III) complexes exhibit reddish-orange luminescence due to 4G5/2→6H7/2 transition at 606 nm of samarium (III) ions. Further, energy band gap, color purity, CIE color coordinates, CCT and quantum yield of all complexes were determined accurately. Replacement of water molecules by ancillary ligands enriched the complexes (S2-S6) with decay time, quantum yield, luminescence, energy band gap and biological properties than parent complex (S1). Interestingly, these efficient properties of complexes may find their applications in optoelectronic and lighting systems. In addition to these the antioxidant and antimicrobial assays were also investigated to explore the application in biological assays.

A green and highly efficient grinding method was adopted to synthesize emerald terbium complexes with 1-cyclopropyl-6-fluro-4-oxo-7-piperazin-1-ylquinoline-3-carboxylic acid as the main organic ligand and 2,2'-bipyridyl, 1,10-phenanthroline, neocuproine, 5,6-dimethyl-1,10-phenanthroline and bathophenanthroline as ancillary ligands. Structural analysis of these complexes was executed via elemental, infrared and 1 H-nuclear magnetic resonance analysis, which confirmed that the ligand coordinated to the metal ion through β-ketone and hydroxyl groups of carboxylic acid. Thermal stability of these complexes was investigated by study of thermogravimetric/derivative thermogravimetric analysis. Photoluminescence properties were investigated by observing emission spectra (400-700 nm), excitation spectra (250-500 nm) and decay time curves for display devices. The emission spectra revealed that an intense peak at 545 nm was observed due to 5 D4 →7 F5 electronic transition, which is responsible for the emerald colour in synthesized complexes, under 353 nm ultraviolet light excitation. The energy band gap and refractive index were determined, which proclaimed the dormant applications of these complexes in semiconductors. Commission Internationale de l'eclairage colour coordinates confirmed that the emerald emission of these complexes lies in the green region. Furthermore, antioxidant, antimicrobial and antimalarial assays of these complexes were also investigated, which confirmed that these complexes are potent for antioxidant, antimicrobial and antimalarial activities.

A systematic computational analysis is integrated with the experimental records like Rietveld and Judd-Ofelt studies to have a deeper insight into the structural and optoelectronic characteristics of Eu 3+ -doped Ba 2 LaV 3 O 11 system. The vanadates used were developed via solution combustion-synthesis (SCS) route, with all ab-initio calculations performed in the density functional framework. The Rietveld refinement over Ba 2 La 0.65 Eu 0.35 V 3 O 11 lattice confirmed the phase purity and crystal structure prototype (monoclinic with P21/a space group). The first-principal routed structure-optimization of the pure host unveiled not only the total energy but also the atomic positions which were unknown till date. The experimental band-gap (3.724 eV) was found to be pretty much comparable to the value obtained computationally (3.482 eV). The partial density of states (PDOS) were analyzed orbital-as well as element-wise to understand the electronic structure in a more comprehensive manner. The calculation of dielectric function yielded the value of many important optical properties like refractive index, extinction-coefficient, optical-conductivity, and loss-function. The photoluminescent (PL) excitation-emission and decay analysis revealed a very efficient energy transfer from vanadate absorption of Ba 2 LaV 3 O 11 to Eu 3+ ; resulting in a significantly intense emission with blue-white-red color tunability. Furthermore, the density-functional assisted PL analysis also provided the Judd-Ofelt parameters (Ω 2 = 3.3175 × 10 −20 cm 2 and Ω 4 = 0.1197 × 10 −20 cm 2 ), radiative-lifetime (2.03 ms), emission cross-sections (10.80 × 10 −22 cm 2 ), quantum efficiencies and radiative rates for 5 D 0 term. All optoelectronic results of Ba 2 La 0.65 Eu 0.35 V 3 O 11 phosphor suggest that it can be used in the nanocrystalline form for white light emitting diodes (WLEDs) while potentially the bulk crystal in laser devices. Moreover, the results of this report may find applications in designing novel material based upon Ba 2 LaV 3 O 11 lattice.

Novel multifunctional Ba5Zn4Y8O21:Tb3+ nanorods, fabricated via solution combustion route, have been found to go in the tetragonal system with the I4/m (87) crystallographic space group. The diffuse reflectance (DR) studies unveiled a band-gap of 3.77 eV for Ba5Zn4Y7.84Tb0.16O21 (most emitting composition). The ultra-violet (UV) excitation at a wavelength of 290 nm for all Ba5Zn4Y8O21:Tb3+ samples produced the characteristics emission peaks corresponding to 5D4 → 7F6,5,4,3 transitions in Tb3+ (used to obtain Judd–Ofelt parameters). The critical distance of energy transfer between neighboring Tb3+ ions was found to be 18.62 A, and helped to shortlist the right mechanism responsible concentration quenching phenomena (dipole–quadrupole). The in-depth analysis of photoluminescence (PL) decay curves and emission spectra of Ba5Zn4Y8O21:Tb3+ nanorods delivered the value of radiative lifetime (1.1934 ms) and total radiative rates from 5D4 state in Tb3+. The radiative probabilities of electric-dipole transitions (extracted from total radiative rates i.e. magnetic-dipole + electric-dipole) were used to calculate the Judd–Ofelt intensity parameters (Ω2 = 3.98 × 10−20, Ω4 = 1.76 × 10−20 and Ω6 = 0.28 × 10−20 cm2). The quantum efficiency of 5D4 state in Ba5Zn4Y7.84Tb0.16O21 phosphor was calculated to be 79% with pure green emission, signifying their potential use in display and lighting devices. As a final point, the high magnitude of emission cross-section of 5D4 → 7F5 (14.84 × 10−20 cm2) transition also claims their promising candidature as a good laser crystal.

A series of blue–green Ba3Gd(1−x)P3O12: xTb3+ nanocrystals has been successfully prepared via the urea-assisted solution-combustion method. Its structure, morphology, energy-transfer mechanism, photoluminescent (PL) excitation-emission and decay time behavior were investigated in detail employing powder X-ray diffraction (XRD), Transmission Electron Microscopy (TEM), Diffuse Reflectance (DR) and PL spectroscopy. The Rietveld analysis exposed the cubic phase of all the nanophosphors with I-43d (220) space group and infers that Gd3+ ions can be well substituted by Tb3+ ions without any major alteration in the crystal prototype of the host lattice. The optical band-gap of the host was calculated to be 4.9 eV, unveiling the high potential as a host for lanthanide activators. Under the excitation at λex = 224 nm, the photoluminescent emission spectra exhibited the two main characteristic peaks at 545 nm and 487 nm as a result of 5D4 → 7F5 (green and magnetic-dipole) and 5D4 → 7F6 (blue and electric-dipole) transitions, respectively. The decay analysis showed that the activator occupies a single crystallographic site, a fact that is also supported by the Rietveld refinement. The critical distance of the energy transfer (19.87 A) integrated with Dexter’s modeling inferred about the energy migration (dipole–dipole). The PL result showed that the blue-to-green tunable emission can be achieved simply via varying the dopant concentration, with 7 mol% as the optimum concentration for standard CIE coordinates of green emission. All the results suggest that Ba3Gd(1−x)P3O12: xTb3+ crystals may find their use as a green phosphor component in display devices and solid-state lighting.

Perovskite orange-red SrLa2(1-x)Al2O7:2xSm3+ (x = 0.01–0.07) nanocrystalline phosphor series were successfully synthesized by means of solution combustion route for the first time. X-ray diffraction (XRD) measurements were performed to analyze the structural framework and it was concluded that the resulted nanophosphors were well-crystallized in tetragonal lattice with the space group I4/mmm (139). The lattice constants and refinement factors for SrLa2Al2O7 and SrLa1.92Sm0.08Al2O7 compositions were obtained by performing Rietveld refinement technique. From transmission electron micrographs, the spherical or semi-spherical nature of highly agglomerated particles (20–30 nm range) was noticed. Further, the diffuse reflectance (DR) studies yielded the band-gaps for SrLa2Al2O7 (5.03 eV) and SrLa1.92Sm0.08Al2O7 (4.88 eV) powder samples. The photoluminescence investigation of nanophosphors revealed the strong orange-red luminescence at 600 nm (most prominent) attributed to 4G5/2 → 6H7/2 emission of Sm3+ ions under near-ultraviolet (NUV) excitation (λex = 407 nm). The optimum composition of Sm3+ in SrLa2Al2O7 lattice was found to be 4 mol%. However, the double exponential decay behaviour confirmed the simultaneous occupancy of two crystallographic sites by activator ions in the host matrix. In addition, the critical distance for non-radiative energy migration amid adjacent activator centres was calculated to be 15.07 A, using Blasse's relation. A detailed analysis of non-radiative relaxation rates (131.9531 s−1), radiative life time (1.79 ms) and quantum efficiencies (81%) was carried out using Auzel's modal. Finally, the results highlight the importance of SrLa2Al2O7:Sm3+ orange-red nanophosphors in white LEDs under NUV excitation.

A series of reddish orange light emitting SrGdAlO4: Sm3+ nanophosphor was prepared by urea aided solution combustion process. Structural features of the prepared nanophosphor were described by the powder X-ray diffraction (PXRD) together with Rietveld refinement technique. The results authenticate the existence of single phased tetragonal lattice with space group of I4/mmm (139). The highly intense peak observed in the photoluminescence emission spectra of the synthesized nanocrystalline phosphors was observed at 600 nm owing to 4G5/2 → 6H7/2 transition upon excitation by 407 nm light. The estimated energy band gap of SrGd0.97Sm0.03AlO4 nanophosphor was found to be 5.45 eV. The critical distance value evaluated for non-radiative energy transfer comes around 17.52 A. The main reason responsible for the observed concentration quenching phenomenon in emission intensity of the prepared nanophosphor beyond 3 mol % doping of Sm3+ was found to be dipole-dipole (d-d) type electric multipolar interaction. The refractive index of the optimized nanophosphor (SrGd0.97Sm0.03AlO4) comes around 1.682. The chromaticity coordinates were found to lie in the reddish-orange region of CIE (Commission Internationale De I'Eclairage) diagram. The vivid description of the photoluminescent and structural aspects validate the potential applications of synthesized nanophosphor as optical nanomaterials in phosphor converted white light emitting diodes (pc-WLEDs).

High-brightness, red-emitting Ca9Gd1−x(PO4)7:xEu3+ phosphors were developed via the facile route of solution-combustion. The Rietveld-assisted structural analysis of Ca9Gd(PO4)7 and Ca9Gd0.40Eu0.60(PO4)7 systems unveiled a trigonal crystal system having R3c(161) space-group symmetry. The absence of JCPDS data was compensated by simulating one from refined structural prototype. The band-gap for the host and best luminescent composition were determined to be 4.55 and 4.01 eV, respectively. The ratio of Judd-Ofelt parameters inferred a very high asymmetry around activator ion which can further be enhanced as a function of dopant concentration. The refractive index of Ca9Gd(PO4)7 was determined to be 2.34. The value of stimulated emission cross section, total radiative transition rate and non-radiative transition rate for Ca9Gd0.40Eu0.60(PO4)7 are calculated from detailed photo-luminescent (PL) analysis. Furthermore, very high value of quantum efficiency (98.13%) and radiative lifetime (1.85 ms) suggested that Ca9Gd0.40Eu0.60(PO4)7 nanophosphor have practical applicability in PC-WLEDs (components of solid-state lighting).

Five novel europium(III) complexes with 2-[4-(dibutylamino)-2-hydroxybenzoyl]benzoic acid (DAHB) as primary ligand and bathophenanthroline (batho), 2,2’-bipyridyl (bipy), 5,6-dimethyl-1,10-phenanthroline (dmph), 1,10-phenanthroline (phen) as ancillary ligands were synthesized via solution precipitation method. The structural formulae of synthesized complexes were speculated to be Eu(DABH)3·2H2O (C1), Eu(DABH)3·batho (C2), Eu(DABH)3·bipy (C3), Eu(DABH)3·dmph (C4) and Eu(DABH)3·phen (C5) by elemental analysis, infrared spectroscopy and proton nuclear magnetic resonance spectroscopy (1H-NMR). The photoluminescent properties and thermal stability of the complexes were investigated by photoluminescent spectroscopy and thermogravimetric analysis (TG-DTG), respectively. The Commission Internationale de I’ Eclairage (CIE) color coordinates, Judd–Ofelt intensity parameter (Ω2), total quantum yield, intrinsic quantum efficiency and energy transfer dynamics of complexes were also explored. The excitation spectra of complexes are extended up to visible region. These complexes exhibit characteristic photoemission of Eu3+ metal ion with high color purity in red region attributed to efficient energy transfer from ligand to metal ion. The replacement of water molecules from coordination sphere of europium ion by ancillary ligands results in enhancement of luminescent properties of the C2–C5 complexes, indicating that ancillary ligands act as additional light harvesting centers in sensitization phenomenon. The thermal studies show that these complexes are suitable for meeting the requirement of temperature for fabrication of OLEDs devices.

An efficient and cost-effective technique, solution combustion synthesis was used to synthesize Dy3+ doped SrGdAlO4 nanophosphor utilizing urea as a suitable fuel. The tetragonal phase and nano-crystallinity of the synthesized phosphor belonging to I4/mmm space group was confirmed by powder X-ray diffraction (PXRD) and transmission electron microscope (TEM) technique respectively. Various crystal structure parameters and refined atomic positions of host matrix and SrGd0.95Dy0.05AlO4 nanophosphor were determined by Rietveld refinement. The two intense bands i.e. blue and yellow bands were observed in photoluminescence emission spectrum recorded at 352 nm excitation wavelength, associated to transitions 4F9/2 → 6H15/2 (484 nm) and 4F9/2 → 6H13/2 (575 nm) respectively. Photometric characterizations revealed the emission of white color by the synthesized nanophosphor proving its wide applications in WLEDs (white light emitting diodes). Band gap values calculated using diffuse reflectance spectra (DRS) were found to vary in the range of 5.50 eV–5.59 eV for host and doped lattice system. Keeping in mind, the concentration quenching phenomenon, SrGd0.95Dy0.05AlO4 was considered as optimized nanophosphor for WLEDs.

Down-conversion Ba5Zn4Gd8O21:Sm3+ reddish-orange nanocrystalline phosphors with high quantum efficiency were well-synthesized by solution combustion route. The structural and morphological characterizations were systematically done via X-ray diffractometry (XRD) and transmission electron microscopy (TEM). Refined atomic positions as well as unit cell parameters for optimum composition were calculated using refinement technique. The results revealed that the substitution of Gd3+ ions by Sm3+ ions in Ba5Zn4Gd7.76Sm0.24O21 nanophosphor did not induce any major structural change and confirmed its tetragonal framework with I4/m (87) space group. TEM studies indicated the rod-shaped morphology with uniform samarium ion distribution of combustion derived nanophosphor ranging from 40 to 90 nm. The energy band-gap values for Ba5Zn4Gd8O21 (5.1 eV) and Ba5Zn4Gd7.76Sm0.24O21 (4.88 eV) were estimated from diffuse reflectance (DR) measurements. Further, the photoluminescence studies upon 410 nm excitation yielded the reddish-orange luminescence (at 610 nm) attributed to 4G5/2→6H7/2 transition of Sm3+ ions. The luminescence intensity of samarium-activated phosphor reached the maximum at the Sm3+ content of 3 mol%, for which the critical separation (RSm-RSm) was ≈ 16.5 A. In addition, the energy relaxation process in Ba5Zn4Gd8O21:Sm3+ was clearly observed, which was confirmed via electric dipole-quadrupole interaction pathway. Besides, the radiative lifetime (1.19 ms), non-radiative relaxation rate (544.31 s−1) and most importantly, the quantum efficiency of 4G5/2 electronic state (60%) were also analyzed in detail. The obtained CIE chromaticity coordinates favour the applications of samarium activated Ba5Zn4Gd8O21 phosphor in near-ultraviolet (NUV) excited tricolor phosphor based white light-emitting diodes (WLEDs).

Color tunable Tb3+ doped SrGd2Al2O7 nanophosphor is synthesized employing a facile and economic urea assisted solution combustion approach. XRD studies confirm the crystallization of single phased SrGd2(1-x)Tb2xAl2O7 nanophosphor in tetragonal lattice with I4/mmm (139) space group. Rietveld refinement is performed over SrGd1.9Tb0.1Al2O7 sample to execute qualitative as well as quantitative phase analysis. TEM analysis confirms the more or less spherical shaped phosphors in nano domain with average particle size ranging 45–80 nm. Photoluminescent investigation reveals that this nanophosphor can be successfully excited by ultraviolet light yielding significant luminescent properties arising due to radiative transitions from 5D3,4 levels to 7Fj levels. Dipole-dipole interactions are solely responsible for the energy transfer causing concentration quenching. Concentration controlled luminescent tendency can be employed to induce chromaticity from blue to green region. Findings of the study proclaim the application of this nanophosphor as one of the green component of tricolor based ultraviolet excited white LEDs.

To improve current multiphase white light emitting diodes (WLEDs), a novel series of five complexes consisting of one binary and four ternary complexes that emitted cool white light was successfully synthesized using a chelating tetradentate ligand and auxiliary ligands, i.e. 5,6-dimethyl-1,10-phenanthroline, 1,10-phenanthroline, 4,4'-dimethyl-2,2'-bipyridyl, and 2,2'-bipyridyl. The series was examined structurally using elemental analysis, Fourier transform infrared spectroscopy, energy dispersive X-ray analysis, ultraviolet-visible spectroscopy, and proton nuclear magnetic resonance spectroscopy. These complexes had the appropriate thermal stability required for the generation of white organic LEDs (WOLEDs). Dysprosium (III) (Dy3+ ) ion complexes demonstrated the characteristic emission peaks of blue colour at 482 nm and yellow colour at 572 nm, respectively, when excited using near ultraviolet light. Band gap, refractive index, and decay lifetime of the optimized samples were recorded as 2.68 eV, 2.12, and 1.601 ms, respectively. Correlated colour temperature value (7875 K), Commission International de l'Eclairage coordinates (0.300, 0.294), and colour purity (21.04 × 10-2 ) of the optimized complex were near to those of white illuminants as defined by the National Television System Committee. These complexes had promise as commercial LEDs for the advanced optoelectronics devices, especially as WOLEDs for illumination applications.

An efficient and cost-effective technique, solution precipitation approach is adopted to synthesize five bright green luminescent terbium (III) complexes by employing the main β-hydroxy ketone ligand, 2-hydroxy-4-ethoxyacetophenone, and ancillary ligands like bathophenanthroline, 5,6-dimethyl-1,10-phenanthroline, 1,10-phenanthroline, and 2,2-bipyridyl. The elemental compositions and binding mode of ligand to terbium (III) ion can be validated by using energy dispersive X-ray analysis, elemental analysis, Fourier transform infrared, and proton nuclear magnetic resonance spectroscopy. The complexes are thermally stable up to 158°C and possess the cubic shaped particles as confirmed by thermogravimetric analysis and scanning electron microscopic study, respectively. The band-gap energy (3.02-2.92 eV) of complexes is reckoned through diffuse reflectance spectra, which tailors them as potential candidates in the field of military radars. The photoluminescence studies unveil that the complexes exhibit the bright green luminescence corresponding to 5 D4 → 7 F5 transition of Tb3+ ion (548 nm) under the excitation wavelength of 395 or 397 nm. The Commission International de I'Eclairage chromaticity coordinates (x, y) and color purity substantiates the green emission of complexes. The energy transfer mechanism elucidates that the main ligand and ancillary ligands sensitize Tb3+ ion, which in turn enhances the luminescence efficiency of the emissive layer of white organic light emitting diodes. The results reveal that the complexes are considered as good contenders in the field of display devices and laser technology. Lastly, in vitro antimicrobial and antioxidant activity proclaim the potent antimicrobial and antioxidant actions of complexes via tube dilution and 2, 2-diphenyl-1-picrylhydrazyl assays, respectively.

Photoluminescent investigation and Rietveld refinement has been performed on trivalent samarium fused Bi4MgO4(PO4)2 -a novel nanophosphor series. The series from 0.5 mol% to 6 mol% dopant concentrations has been developed by means of a time efficacious path of solution combustion synthesis (SCS) fueled by urea. The X-ray powder diffraction patterns for complete Bi4(1-x)Sm4xMgO4(PO4)2 (x = 0.005–0.06) nanophosphor series being in accordance with that of pure host comply of phase purity. The arrangement in space group Pbca(61) and crystallization in orthorhombic cell of Sm3+ doped Bi4MgO4(PO4)2 is recognized by Rietveld refinement. The bivalent Mg ions as a part of [(PO4)2MgBi2O2]2- slabs are present alongside [Bi2O2]2+ planes in the unit cell. In host Bi4MgO4(PO4)2, the diffuse reflectance spectrum led calculations give an optical band-gap of 3.87 eV. The PL emission spectra mark 2 mol% as the optimal fluorescent composition and the emission intensity declines for further compositions. It is credited to concentration quenching phenomena due to dipole-dipole energy exchanges as observed by Dexter's theoretical model. The decay curves for Sm3+ doped phosphate-based nanophosphor bear bi-exponential decay behavior and hence, the average PL lifetime values derived are used in the Auzel's model to obtain the magnitude of radiative lifetime. The transmission electron microscopy operated at high -resolution (HRTEM) and field emission scanning electron microscopy (FE-SEM) inform about the polycrystalline and morphological behavior of the synthesized nanophosphor. The elemental purity of the sample is confirmed by the energy dispersive spectroscopy (EDS). The PL as well as decay curves are inspected to gain the quantum efficiencies and non-radiative rates for Sm3+ doped Bi4MgO4(PO4)2 nanophosphors. The analysis related to different parameters as well as chromaticity coordinates (x = 0.517, y = 0.480) and quantum efficiency (94%) espouse Bi3.92Sm0.08MgO4(PO4)2 for relevance in solid state lighting (SSLs) expedients.

A series of Eu3+ ion doped SrGdAlO4 nanophosphors were prepared via solution combustion technique utilizing urea as a fuel. Structural properties of the tetragonal phase of the host/doped lattice belonging to the space group I4/mmm were characterized by powder X-ray diffraction (PXRD). Photoluminescence spectra, decay curves, UV–Visible diffuse reflectance spectra (UV–Vis DRS) and Judd–Ofelt analysis were utilized to characterize the photoluminescent properties. The radiative rates (Ar), branching ratios (Br) and intensity parameters (Ωλ) were estimated by Judd–Ofelt analysis. The optimal doping concentration of europium ions for SrGdAlO4 host lattice was found to be 20 mol%, above which concentration quenching was observed due to dipole–dipole interactions. CIE coordinates values lie in the blue region at lower concentrations of Eu3+ ions, which shifted towards white and then to reddish-orange region with higher concentrations of Eu3+ ions, suggesting the color tunable property of the synthesized nanophosphors. Lower value of CCT and color tunable phenomenon proved it as potential candidate for warm white light and phosphor converted white light emitting diodes (Pc-WLEDs) applications. The optical band gap of both host lattice (5.50 eV) as well as of 20 mol% Eu3+ doped SrGdAlO4 nanophosphors (5.26 eV) lie in the range of semiconductors which enhanced their areas of applications.

Eu3+ doped Ba2YAlO5 nano-crystalline phosphor is synthesized for the first time using urea assisted solution combustion approach. X-ray diffraction analysis depicts that single phased Ba2Y(1-x)EuxAlO5 sample obtained by post heat treatment for 4 h at 1225 °C crystallize in monoclinic lattice with P21/ (11) space group. Transmission electron microscopy (TEM) studies reveal semi-spherical shaped particles in nano dimension ranging 40–90 nm. Photoluminescent studies elicits that this nanophosphor can be efficiently excited by NUV light generating emission in the red region. Ba2Y0.95Eu0.05AlO5 is found to be the optimal composition for achieving the maximum luminescence. Concentration controlled luminescent behavior can be utilized to obtain the chromatic color tuning from blue to red region. Luminescent centres shows cross relaxation via quadrupole-quadrupole interactions beyond 5 mol% concentration of Eu3+ ion leading to concentration quenching. Judd-Ofelt intensity parameters and refractive index of host are also determined. Chromatic color tuning proclaim the possible utilization of this nano-crystalline phosphor in NUV excited solid state lighting devices.