Rare earth based luminescent materials have emerged as a focal point of the scientific investigation owing to their remarkable optical behaviour and potential applications. An effort has been made to develop a series of Ce3+ doped CaWO4 nano-phosphors using an ethylene-glycol assisted reflux route. The detailed structural and morphological properties have been examined through various analytical techniques. The +3-oxidation state of the activator ion Ce has been verified through the XPS study. The change in optical band gap due to the substitution is well discussed using diffuse reflectance spectroscopy. In Photoluminescence study, a broad emission centred at 465 nm is observed due to the 5D3/2 -> 2FJ transitions (J = 7/2 and 5/2) and a significant enhancement in the emission peak is obtained for the optimized phosphor. Concentration quenching phenomenon, observed after 3 mol% of Ce3+ is mainly mediated by the electric multipole-multipole type interaction. The CIE diagram indicates the tuning of emission colour from blue to white region and the emission near white region for the optimized phosphor is further authenticated by its low colour purity value (43 %). The effective tunability of photo-physical properties and colorimetric parameters suggest the applicability of the optimized nano-phosphor in solid state lighting especially for outdoor illumination.

Self-activated tungstates doped with lanthanide ions are an excellent class of phosphor materials, exhibiting promising luminescence efficiency as well as stability which opens up their vast arena of applications. In this work, a detailed comparative study has been carried out on Sm3+ doped Ba/CaWO4 phosphors, synthesized via solid state reaction route. The structural, morphological and photo-physical properties have been investigated through various analytical techniques. The optical band gap and the refractive index of the phosphors have been estimated through diffuse reflectance spectroscopy. A 5-fold enhancement of the emission intensity is observed in CaWO4 as compared to BaWO4 phosphors owing to high asymmetrical environment. The underlying mechanisms of photoluminescence and energy transfer process (WO42+-Sm3+) are discussed in detail. The colour tuning from orange red to pure red emission is obtained from the Commission International de l ' Eclairage (CIE) diagram. Better luminescent properties with desirable quantum yield, absorption efficiency and suitable Correlated Colour Temperature (CCT) and colour purity (91 %) values allow the optimised phosphors for diverse potential applications such as solid-state lighting, security ink for anti-counterfeiting, latent fingerprint detection, etc.

Ferroelectric (FE) materials and their advancements have piqued the scientific community’s interest greatly since they provide numerous fascinating processes in addition to being used in devices. Among them, we have studied Mn and Sn co-doped PZT and Pb (Zr0.52Ti0.48) O3 as PZT, an extremely intriguing FE. The structure and phase purity of all the samples are determined by x-ray diffraction techniques. All the samples show a very good microstructures and the average grain size is found to be decreased with ion incorporation. The UV-Vis spectra show how doping reduces optical band gaps. Parallel resistance (R)-capacitance (C) circuits have been used to analyze the relationship between microstructure and electrical characteristics. The microscopic processes in various PZT samples with dilute magnetic cations at A-sites, B-sites, and/or both sites at the morphotopic phase boundary are established from the detail impedance, modulus, and ac conductivity of the samples as a function of temperature (300 –500 °C) and over a range of frequency (100 Hz to 1 MHz). Additionally, the framework of the Jump relaxation model and the Jonscher power law are used to study the ac-conductivity data.

A series of Sm and Mn co-doped nanoparticles are synthesized through ethylene glycol assisted sol–gel route to study the impact of both rare earth ions and Mn on the structural, magnetic and low temperature electronic behaviour in LaFeO 3 . The Rietveld analysis of X-ray diffraction data shows a single phase nature of the nanoparticle with distorted orthorhombic crystal structure. The unit cell volume reduces with increasing Mn, is due to the ionic radii differences between the cations which cause crystal lattice contraction because of the distortion of Fe/MnO 6 octahedra. Mostly, particles are agglomerated with an average particle size of 38.5 nm. From the XPS spectra, the existence of multivalence state of both Fe and Mn are obtained. This multiple state of transition metal ions along with Sm are expected to play a major role in the magnetic interactions and other related properties. A drastic magnetic disorder phase is acquired by the modified systems at low temperature as compared to the pure G-Type LaFeO 3 . Furthermore, the modified nanoparticle shows a colossal dielectric response (> 10 3 at 100 Hz) and the obtained dielectric relaxation follows mostly non-Debye type which is further confirmed through explicit modulus spectra analysis. From the impedance, modulus and ac-conductivity analysis, the conduction processes in the modified systems reveal a possible N-type and P-type polaronic conduction for both the grain and grain boundary.

KBiFe2O5 (KBFO) is one of the oxygen deficient perovskites which specifically comes under brownmillerite family. In this work, structural and electrical properties of KBFO has been investigated. Polycrystalline sample of KBFO is effectively prepared by citrate combustion method. Deriving out of Rietveld refinement of X-ray powder diffraction (XRD), KBFO conforms that, the sample is crystallized in monoclinic structure having P2/c space group. To know the surface morphology of the sample, scanning electron microscope (SEM) study is carried out. KBFO contains grains with different size in a micrometer range. Frequency dependent dielectric permittivity (ε′) of KBFO is investigated over a frequency range 100 Hz –1 MHz at some selected temperature and the data is well fitted with Modified Debye model. From the fitted results, KBFO manifests non Debye type of relaxation. To explore the conduction mechanism, grain and grain boundary contribution of the sample, frequency dependent ac conductivity measurement is carried out at a frequency and temperature range 100 Hz-1 MHz and 503 K- 603 K respectively. It is observed that ac conductivity shows an increasing order with increasing temperature. Jonscher′s power law is used to verify ac conductivity with frequency graph. Based on the fitted parameters, it is found that the power exponent (n) decreases with increasing temperature which indicates the conduction process in KBFO follows correlated barrier hopping (CBH) model.

Core nanoparticles (NPs) and core-shell particles have been synthesized using the low temperature reflux method. The structural and photo-physical properties of the developed phosphors have been investigated through various analytical techniques. The transmission electron microscopy (TEM) analysis evidences the formation of the shell on the core NPs. The optical band gap is estimated using the diffuse reflectance spectra. An 8-fold enhancement of emission intensity is observed in the core-shell particles as compared to that of core, due to the reduced surface quenchers after silica coating. In addition, the Judd-Ofelt (J-O) parameters have been calculated to reveal the site symmetry and coordination environment around Eu3+ ions. The tunable red emission on formation of core-shell structures is confirmed from the CIE diagram. These results are ascribed to the formation of the chemical bonds between CaWO4@ CaWO4:3%Eu3+:5%Bi-3+ (core) and amorphous SiO2 shell via W-O-Si bridges. Better hydrophilicity developing from active functional groups in solutions and intense luminescence behavior with a quantum efficiency of 91% allow the developed phosphors for various potential applications such as solid state lighting, bio-labelling agent for the visualization of latent fingerprints (LFPs) and anti-counterfeiting, etc.

Nanoparticles as contrast agents for in-vitro and in-vivo imaging is the most astounding, non-invasive method developed by researchers in the present scenario. To improve the multifunctionality of bio-imaging field, both Magnetic resonance imaging (MRI) and fluorescence based nanoconstructs are appreciated. In this regard, current research is dedicated to fabricate Fe3O4@NaGdF4 core–shell structure as a multifunctional, efficient probe to be useful for said purpose. Concerned core–shell is constructed in layer-by-layer approach with Fe3O4 and NaGdF4 served as core and shell respectively. Phase purity of sample is investigated through X-ray diffraction (XRD) data, seen to have inverse spinel phased Fe3O4 core and hexagonal NaGdF4. Field emission scanning electron microscopy (FESEM) images clarified the average dimension of isolated core and shell grains to be 59.86 and 62.20 nm respectively. Formation of Core-shell is verified through HRTEM images. Fourier transform infrared (FTIR) spectroscopy data reveals the functional group associated with the corresponding components. Magnetic criteria of sample are studied through room temperature magnetic field dependent magnetization (M−H) data in the range of ± 1.5 Tesla. Non-magnetic shell is seen to be dominate on magnetic core for reducing the magnetic saturation value to 9.104 emu/g from 37.891 emu/g of isolated Fe3O4 sample. Downshifting luminescence is also detected through photoluminescence (PL) study in Ultraviolet (UV) B range (309 nm) due to excitation in UVC region (271 nm) of Gd3+ energy states.

Superconducting NbTiN thin films have garnered extensive interest due to their use in Superconducting Nanowire Single-Photon Detectors (SNSPDs) and other low-temperature applications for potential use in quantum computing and nanoelectronics. This study examines structural phase transitions observed in NbTiN thin films by analyzing the grazing angle x-ray diffraction patterns of a set of reactive magnetron sputter deposited NbTiN thin films with varying nitrogen partial pressures in the reactive gas mixture. The superconducting transition temperature (T_C) of the NbTiN thin films showed a correlation with the crystal structure, with the highest T_C of 14.26 K obtained for the highly crystalline FCC phase.

In this report, impact of co-doping of samarium (Sm3+) and iron (Fe3+) on structural, dielectric and magnetic properties of YCrO3 compound has been investigated. Here, YCrO3 and Y1-xSmxCr1-yFeyO3 (x = 0.3, y = 0.1) compounds are synthesized successfully through sol–gel auto combustion route. The synthesized samples are characterized through X-ray diffraction (XRD), surface electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), impedance analyzer and vibrating sample magnetometer (VSM) techniques. Rietveld refinement of XRD analysis reveals that both the compounds are crystallized in distorted orthorhombic structure belongs to Pnma space group. It is observed that with co-doping of both Sm3+ and Fe3+, lattice unit cell volume increases. SEM micrograph shows that the grains are slightly elongated as compared to the undoped sample. The temperature variation of real part of dielectric permittivity (εr) and tangent loss (tan δ) are analyzed over a frequency range 40 KHz − 500 KHz at a temperature range 300 K − 523 K. The temperature dependent dielectric permittivity reveals that both εr and tan δ decrease with co-doping. Moreover, both the compounds show relaxor like ferroelectric transition. Room temperature field dependent magnetization analysis shows that maximum magnetization value increases with co-doping. The result reveals that the enhanced properties with co-doping can be useful for practical device applications.

Effect of simultaneous Sm and Mn substitutions around half-doping level on the structural, magnetic and low temperature electronic behaviour of LaFeO3 nanoparticle is extensively studied. The SXRD and FESEM data shows a single-phase nanoparticle of size 33 nm. A drastic magnetic phase change with a low temperature non-ergodic phase is seen compared to the parent LaFeO3 (G-type antiferromagnetic) and this typical behaviour stems from the facts that, simultaneous presence of Sm and Mn alters the Fe crystal environment as well as its multiplicity which leads to improved exchange interactions among different ions. The doped nanoparticle shows a colossal dielectric response. Impedance, modulus spectra and ac conductivity analysis are used to find the conduction process involved in the system and it is related to the hopping conduction through grain and grain boundary resistances. The possibility of the polaronic part may arise from the interactions among mixed-valence state of Fe (Fe3+/Fe2+), Mn (Mn3+/Mn2+) and from the oxygen vacancies. Moreover, the ac-electrical conductivity is analysed using Jonscher's double-power law and Jump relaxation model.

M- Type hexaferrite captivates researchers and industrialists for its diverse usage and applications in different fields such as permanent magnets, storage devices, recording media, radar absorbing materials and many more. In this work, Sm3+ substituted Strontium hexaferrite, Sr1-xSmxFe12O19 (x = 0, 0.05) is synthesized by using ethylene glycol aided sol–gel auto combustion technique. X-Ray Diffraction Technique is employed for the understanding of various structural features. Phase purity of the prepared samples is authenticated by performing Rietveld refinement method. All the studied samples crystallizes in hexagonal magneto-plumbite phase with P63/mmc space group. Crystallite sizes are determined using Scherer equation. Field Emission Scanning Electron Microscopy is used for morphological analysis. Average particle size decreases with Sm3+ substitution in comparison with parent one. Both field and temperature dependent magnetization measurements are accomplished for magnetic properties analysis. Hysteresis curves show Coercivity (Hc) value increases more than two times and saturation magnetization (MS) decreases slightly as compared to parent sample which clearly indicates that the sample can be used as hard ferrites. M−T measurements are carried out with the application of 500 Oe field. Both the sample show transition around 500 °C temperature. Substituted sample also shows a prominent Hopkinson peak in comparison with parent sample.

A series of xMg2+/ySc3+ co-doped beta-NaYF4:0.2Yb3+/0.02Ho3+ (x = y = 0 -0.2) upconversion (UC) green phosphors are synthesized using EDTA-assisted hydrothermal method. The structure, morphology and elemental compositions are investigated in detail using different experimental techniques. The lengthwise suppression of crystal due to co-doping is associated to the kinetics involved in the crystal growth in presence of Mg2+/Sc3+. The effect of Mg2+/Sc3+ co-doping on the UC green emission of beta-NaYF4:0.2Yb3+/ 0.02Ho3+ microphosphors is studied and about 31-fold enhancement in the green emission (5F4,5S2 -> 5I8) is observed for the 0.08Mg2+/0.12Sc3+ co-doped phosphor. The downconversion properties of the phosphors is also discussed to showcase the dual mode luminescence. The temperature sensing performance is in-vestigated using luminescence intensity ratio (LIR) technique for non-thermally coupled levels (5F5/5F4,5S2) of Ho3+ ions and maximum relative sensitivity of 0.258% K-1 at 374 K is obtained for the optimized phos-phor. The microphosphor can be sustained at high temperature as the UC emission intensity retains about 65% and 36% at 423 K and 574 K. From chromaticity diagram, the maximum color purity of 91.37% is obtained for 0.08Mg2+/0.12Sc3+ doping concentration. The estimated thermal parameters and color purity of Mg2+/Sc3+ co-doped beta-NaYF4:0.2Yb3+/0.02Ho3+ UC phosphors suggest their applicability in fabricating temperature sensors and LEDs. (c) 2022 Elsevier B.V. All rights reserved.

Dual sensitized phosphors owing to their efficient energy transfer and wide spectral range have grabbed the attention of the scientific community to sort out the issue of poor luminous efficacy and simultaneously improve their applicability. Herein, a series of doubly sensitized (Bi3+/Mn2+) and Dy3+ activated YVO4 phosphors have been synthesized adopting the high temperature solid state reaction route and characterized through various analytical techniques. The tetragonal zircon type structure is confirmed from the XRD patterns supported by quantitative Reitveld refinement. The emission spectral profile reveals a wide spectral range of Dy3+ covering blue, green and red region with two-fold enhancement in the luminescence intensity due to double sensitization by Bi3+/Mn2+. The underlying energy transfer mechanism is also discussed in detail to showcase the dual sensitization of the activator ions. The CIE coordinates indicate the spectral tuning towards the white region and the low color purity percentage shows its purity towards white color. Furthermore, the CCT value favours cool white feature of the phosphor. Thus, Bi3+ and Mn2+ doping reflects in enhancing the emission intensity, thereby increasing the applicability of these Dy3+ activated phosphors in the field of solid state lighting.

Upconversion emission in CaWO4:Er3+/Yb3+/Mn2+ phosphor synthesized via ethylene glycol route has been analyzed on excitation under 980 nm diode laser. The structural information and morphology have been widely studied through different experimental techniques. The Yb-Mn dimer is inserted to explicate the energy transfer mechanism which brings about twofold enhancement in the green emission. The optical thermometric perfor-mance of the developed phosphor based on the thermally coupled green levels of Er3+ (2H11/2 and 4S3/2) ions in the range of 303-623 K has been explored using the fluorescence intensity ratio (FIR) technique. The maximum sensitivity of 1.04 % K-1 at 303 K is obtained for the optimized phosphor with a thermal resolution of 0.4 K. Additionally, the internal heating characteristics of the said phosphor developed by the variation in excitation laser power is also studied which is found to raise from 265 to 563 K. Under 980 nm excitation the prepared phosphors exhibit strong green emission with a color purity of 98 %. The energy transfer mechanism, population redistribution ability and thermal stability have been discussed in detail and the possible field of applications have been explored.

An interesting rather intriguing consequence of Pb-2(+) upon the structural, dielectric and magnetic properties are studied in Strontium Hexaferrite (SrFe12O19). The ethylene glycol assisted sol-gel autocombustion technique is adopted for the synthesis of hexaferrites. Structural aspects of the SrFe12PbxO19 (x = 0, 0.1) is extensively carried out by using X-Ray Diffraction technique. Phase purity of the prepared samples is confirmed by performing rietveld refinement analysis. The parent as well as doping sample both crystallizes in a space group P6(3)/mmc. An extensive dielectric study of the prepared sample is carried out from 30 degrees to 400 degrees C over the frequency range from 100 Hz to 1 MHz From the frequency dependent behaviour it is realised that dielectric constant along with loss tangent decrease with increase in frequency and achieve a steady value at elevated frequency range. Similar behaviour is also can be seen in doping system but attains a smaller value. Furthermore, this behaviour is convenient with Maxwell-Wagner model along with Koop's phenomenological theory. Field dependent magnetization plots show usual hysteresis loops. However saturation magnetization decreases and coercivity increases with doping in comparison with the parent compound. This shows that the samples can be used in storage devices. Copyright (C) 2022 Elsevier Ltd. All rights reserved.

A series of beta-Na(Y0.95-x,Gd-0.05)F-4: xEu(3+) (x = 0 - 0.15) microphosphors with minimal concentration of Gd3+ is developed using modified hydrothermal techniques. The phase purity, structure, morphology, el-emental distributions and surface chemical compositions are investigated by X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy, energy dispersive X-ray analysis and X-ray photoelectron spectroscopy analysis. Characteristics photoluminescence emissions of Gd3+ (P-6(7/2) > S-8(7/2)) and Eu3+ (D-5(0) -> F-7(j)) are observed in the doped and codoped phosphors by indirect and direct excitations at 272 nm (of Gd3+) and 394 nm (of Eu3+) respectively. Strong PL emissions at 310 nm of Gd-doped beta-NaYF4 at an excitation of 272 nm suggests its possibility in phototherapy applications. The observed Omega(2) > Omega(4) from the Judd-Ofelt model suggests a local asymmetricity around Eu3+ ions in the studied microphosphors. The emission peak intensity at 615 nm varies with Eu3+ concentrations and quenching occurs at higher doping level. Moreover, the emission spectra and luminescence lifetime based on Inokuti-Hirayama model reveals an efficient energy transfer from Gd3+ to Eu3+ is mainly mediated through dipole-dipole interaction. A detail schematic representation of the energy transfer process between activator ions is also documented. Comparatively a better emission color tunability and color purity (90.08%) of red emission is achieved in Gd3+-Eu3+ doped phosphors for indirect excitation of Eu3+ ions at 272 nm. The effective tunability of the photophysical properties of these UV excitable phosphors suggest its applicability in fabricating wLED using UVchips, spectral converters for solar cell and bio-labeling etc. (C) 2022 Elsevier B.V. All rights reserved.

In the present study, Sm3+ activated inorganic orthophosphate CsMgPO4 (CSMP) phosphors were prepared by adopting a solid-state reaction method. The structural phase purity and morphological features were studied by X-ray powder diffraction (XRD) and scanning electron microscopy (SEM), respectively. The molecular structure and vibrational modes were substantiated with the Fourier transform infrared spectroscopy (FTIR) and Raman spectroscopy characterization. The optical bandgap of the host and Sm3+ doped phosphors was deduced from the diffused reflectance (DR) spectra with a typical value of 5.72 eV and a small variation is observed with increasing concentrations. A systematic study of photoluminescence (PL) properties of Sm3+ doped CSMP phosphors was carried out. From the room temperature excitation and emission spectra, it is found that the phosphor emits in the orange rich red light under the suitable excitation of 402 nm in the UV region and concentration quenching occurs at x = 0.02 doping level. The emission peaks observed at around 562, 598 and 644 nm confirm the characteristic Sm3+ 4f-4f transitions. The temperature-dependent photoluminescence (TD-PL) of the x = 0.02 (optimum doping) is recorded from 30 to 210 degrees C, showing good thermal stability even at 150 degrees C. The thermal quenching mechanisms are discussed based on the configuration coordinate model of excitation and emission. The prepared phosphors are found to exhibit near thermal stability compared to the commercially available red phosphors. PL decay time and quantum efficiency were measured. The colour coordinates are found to lie in the orangish-red region of the colour space. Thus the prepared phosphors CSMP:x Sm3+ can be useful as a red component in designing UV excitable chip-based phosphor-converted white LED applications. (c) 2022 Chinese Society of Rare Earths. Published by Elsevier B.V. All rights reserved.

We report a significant effect of Aluminum (Al3+) substitution on the structural, optical and dielectric properties in brownmillerite KBiFe2O5 (KBFO) multiferroic. Polycrystalline samples of KBiFe2-xAlxO5 (x = 0, 0.2) are synthesized by citrate combustion method. From the Rietveld refinement of X-ray diffraction analysis, both the samples are found to crystalize in a monoclinic structure possessing P2/c space group. The calculated crystallite size from the Scherer's formula is found to decrease with Al doping. The surface morphology reveals that, multiple grains of different sizes are present in all the samples and the average grain size is reduced with substitution. The optical band gap decreases from 1.739 eV to 1.715 eV with x = 0.2 of Aluminum. Furthermore, the temperature dependent Dielectric constant (epsilon) and dielectric loss (tan delta) of KBiFe2-xAlxO5 are investigated in a temperature range (300-773 K) at 100 Hz and 1 KHz frequency shows a substantial variation followed by a transition at around 550 K for all the samples. A comparative analysis for both the systems reveals that, for x = 0.2 of Al, an order of increase of dielectric constant appears as compared to the parent system. Additionally, the dielectric loss is also found to decrease with doping as compared to pure KBFO. Copyright (C) 2022 Elsevier Ltd. All rights reserved. Selection and peer-review under responsibility of the scientific committee of the 3rd International Conference on Processing and Characterization of Materials 2021 (ICPCM 2021).

A 15-fold intense green emission at 545 nm is observed in a Tb 3+ -activated (Y, Gd)F 3 nanophosphor with high Tb 3+ content and minimal Gd 3+ concentration.

Efficient utilization of phosphors in solid-state lighting and phosphor-converted light-emitting diodes demands high emission intensity, narrow size distribution, and tunable luminescence. Here in this work, un-doped and Li+ co-doped CaMoO4:Dy3+ nanoparticles are synthesized via modified reflux method in ethylene glycol medium at 130 degrees C. The host shows broad dual band emission centered in blue and green regions endowed by charge transfer and defects. Upon Dy3+ doping, the host-to-dopant energy transfer causes the CaMoO4:Dy3+ nanoparticles to exhibit characteristic emission lines from Dy3+. The Commission Internationale de L'Eclairage (CIE 1931) chromaticity coordinates for the prepared phosphors are estimated and found to lie in the nearly white region of color space. The light output as well as excited state lifetimes are successfully improved by lithium co-doping by virtue of reduced charge compensating defects and sensitization via oxygen-related defects. The positron annihilation studies show that all the lithium concentration co-doped for charge compensation is merely helping in the removal of cations. This work shows the role of lithium co-doping and its optimum concentration in improving the optical properties of phosphors.