Nanocrystalline mixed Ni1-xZnx Fe2O4 (x = 0.0, 0.2, 0.4, 0.6, 0.8 and 1) have been achieved by low temperature self-combustion technique using oxylyldehydrazide (ODH) as fuel. The structural, ...morphological and dielectric properties were studied using X-ray diffraction (XRD), Scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), Raman Spectroscopy and frequency dependant impedance spectroscopy with frequency range from 1 Hz to 107 Hz. The XRD analyses of as prepared samples show single phase cubic spinel structure with Fd-3m space group. The average crystallite size was estimated using Debye-Scherer's formula and was found to be in the range 15–30 nm. FTIR spectra shows two prominent absorption bands, the higher band at tetrahedral (A) sites and the lower band at octahedral (B) site. The Raman peaks above 600 cm−1 correspond to A1g type, involving motions of O atoms in the tetrahedral group (A-site) and the other low frequency peak 241, 335 and 480 represent the characteristics of the octahedral group (B-site) of ferrites. SEM images shows that all the samples have nano crystalline behavior with spherical shape. EDX confirms the constitutional distribution of prepared samples. The dielectric properties such as dielectric constant ε′, dielectric loss tangent and ac conductivity were found to be lowest for x = 0.8. The grain and grain boundary contributions in nano ferrites have been explained using Nyquist plot. The prepared mixed ferrites are good material for frequency dependent applications.
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•Mixed Ni–Zn ferrites were prepared via low temperature self-combustion technique using ODH as fuel.•The structural characterization of the prepared sample confirms the nanocrystalline nature.•Dielectric properties of ferrites can be tuned by the composition.•The prepared samples are good material for frequency dependent applications.
A series of scheelite-type Eu
3+
-activated CaMoO
4
phosphors were synthesized by the nitrate–citrate gel combustion method. All the compounds crystallized in the tetragonal structure with space ...group
I4
1
/a
(No. 88). FESEM results reveal the spherical-like morphology. The CaMoO
4
phosphor exhibited broad emission centered at 500 nm under the excitation of 298 nm wavelength, while Eu
3+
-activated CaMoO
4
shows an intense characteristic red emission peak at 615 nm at different excitation wavelengths, due to
5
D
0
→
7
F
2
transition of Eu
3+
ions. The intensities of transitions between different
J
levels depend on the symmetry of the local environment of Eu
3+
ions and were estimated using the Judd–Ofelt analysis. The high asymmetric ratio revealed that Eu
3+
occupies sites with a low symmetry and without an inversion center. The CIE chromaticity co-ordinates (
x
,
y
) were calculated from emission spectra, and the values were close to the NTSC standard. Therefore, the present phosphor is highly useful for LEDs applications.
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•BaMoO4: Eu3+ phosphors were synthesized using nitrate–citrate gel combustion method.•Host BaMoO4 phosphor revealed white emission upon excitation at 370nm.•Eu3+-activated BaMoO4 ...exhibited red luminescence which was confirmed by CIE chromaticity diagram.•Judd–Ofelt parameters and other radiative properties of Eu3+-activated BaMoO4 have been determined.•These phosphors can be used in red lasers and optical display devices.
Eu3+-activated BaMoO4 phosphors were synthesized by the nitrate–citrate gel combustion method. The Rietveld refinement analysis confirmed that all the compounds were crystallized in the scheelite-type tetragonal structure with I41/a (No. 88) space group. Photoluminescence (PL) spectra of BaMoO4 phosphor reveals broad emission peaks at 465 and 605nm, whereas the Eu3+-activated BaMoO4 phosphors show intense 615nm (5D0→7F2) emission peak. Judd–Ofelt theory was applied to evaluate the intensity parameters (Ω2, Ω4) of Eu3+-activated BaMoO4 phosphors. The transition probabilities (AT), radiative lifetime (τrad), branching ratio (β), stimulated emission cross-section (σe), gain bandwidth (σe×Δλeff) and optical gain (σe×τrad) were investigated by using the intensity parameters. CIE color coordinates confirmed that the BaMoO4 and Eu3+-activated BaMoO4 phosphors exhibit white and red luminescence, respectively. The obtained results revealed that the present phosphors can be a potential candidate for red lasers and white LEDs applications.
A low cost and simple method for fabrication of a gas sensor device was developed using reduced graphene oxide (rGO)-doped poly (3, 4-ethylenedioxythiophene)-poly (styrenesulfonate) (PEDOT-PSS) ...organic thin film for the detection of ammonia gas at room temperature. Scanning electron microscopy, atomic force microscopy, Fourier transform infrared spectroscopy, X-ray photospectrometry and thermogravimetric analysis were used for the analysis of morphological, structural and thermal behavior of the prepared thin films. The doping of reduced graphene oxide in PEDOT-PSS was observed to increase the conductivity of pristine PEDOT-PSS thin films by threefold. The gas sensing mechanism of pure and doped PEDOT-PSS thin films were studied at room temperature by fabricating the sensor device on indium tin oxide-coated glass substrate. The gases such as ammonia, carbon monoxide, nitrogen dioxide and nitrogen were used to test the sensing performance in the prepared thin films. The reduced graphene oxide-doped PEDOT-PSS thin films show improved sensitivity towards all test gases, mainly toward ammonia gas with fast response and recovery times. The gas sensitivity of 10 wt% rGO-doped PEDOT-PSS thin film was observed to be about 87% for ammonia gas. The sensor stability test shows that, the prepared sensor is highly stable even after a period of 1 month. Due to improved sensitivity, stability and improved response and recovery times, these rGO-doped PEDOT-PSS organic thin films could be used to detect ammonia gas at low concentrations at room temperature.
•New method for estimation of vocal tract system characteristics from short segments of speech.•Zero-time windowing using an impulse-like window function provides temporal resolution.•Additive ...property of the group delay function provides the spectral resolution.•Robust to additive noise degradations.•Outperforms short-time Fourier analysis, LP analysis and STRAIGHT analysis methods in estimating second and third formants.
Traditional methods for estimating the vocal tract system characteristics typically compute the spectrum using a window size of 20–30ms. The resulting spectrum is the average characteristics of the vocal tract system within the window segment. Also, the effect of pitch harmonics need to be countered in the process of spectrum estimation. In this paper, we propose a new approach for estimating the spectrum using a highly decaying window function. The impulse-like window function used is an approximation to integration operation in the frequency domain, and the operation is referred to as zero-time windowing analogous to the zero-frequency filtering operation in frequency domain. The apparent loss in spectral resolution due to the use of a highly decaying window function is restored by successive differencing in the frequency domain. The spectral resolution is further improved by the use of group delay function which has an additive property on the individual resonances as against the multiplicative nature of the magnitude spectrum. The effectiveness of the proposed approach in estimating the spectrum is evaluated in terms of its robustness to additive noise, and in formant estimation.
In this paper, a new method for voiced/nonvoiced detection based on epoch extraction is proposed. Zero-frequency filtered speech signal is used to extract the instants of significant excitation (or ...epochs). The robustness of the method to extract epochs in the voiced regions, even with small amount of additive white noise, is used to distinguish voiced epochs from random instants detected in nonvoiced regions. The main feature of the proposed method is that it uses the strength of glottal activity as against using the periodicity of the signal. Performance of the proposed algorithm is studied on TIMIT and CMU ARCTIC databases, for two different noise types, white and vehicle noise from the NOISEX database, at different signal-to-noise ratios (SNRs). The proposed method performs similar or better than the popular normalized crosscorrelation based voiced/nonvoiced detection used in the open source utility wavesurfer , especially at lower SNRs.
In this report, LaAlO
3
:Dy
3+
nanophosphors were synthesized via combustion synthesis utilizing sucrose as a fuel. The phase of the prepared phosphors was confirmed by Powder X-Ray Diffraction ...(PXRD) pattern which exhibited rhombohedral pure phase. The optical band gap of the fabricated phosphors was estimated to be of the range of 5.28–5.47 eV. The nanoparticle structure of the prepared nanophosphors is examined with the scanning electron microscope (SEM) images. Transmission electron microscope (TEM) image was taken to access the crystallite size of the prepared samples. Under excitation wavelength of 352 nm, the photoluminescence (PL) emission peaks centered at 490 nm 560 nm, and 666 nm attributed to Dy
3+
ions characteristics. The effect of quenching on luminescence has been explored in detail. The CIE coordinates lie in the white emission with the color purity (CP) of 67%. The quantum efficacy (QE) of the prepared nanophosphors was found to be ~70%. The cathodoluminescence studies of the prepared LaAlO
3
:Dy
3+
phosphors were performed at RT and showed good CL intensity at low voltage. These outcomes validate the prominence of LaAlO
3
:Dy
3+
phosphors to be used in the field of photovoltaic and display devices.
Present paper reports the study on luminescence and optical behaviour of samarium doped lanthanum oxychloride (LaOCl:Sm3+) nanophosphor for their potentiality in display devices. The conventional ...solid state route was employed to synthesize the phosphor La1-xSmxOCl (x = 0, 0.01, 0.03, 0.05, 0.07 and 0.09). Tetragonal phase of the prepared compound was confirmed by PXRD. An agglomerated and spherical like structure were seen of the samples from FE-SEM analysis. The Wood and Tauc relation was employed to find out band gap energy and is around 4.23 eV. At an excitation wavelength of 408 nm, a high intense peak of emission was observed at 608 nm for transitions (4G5/2 → 6H7/2) of Sm3+ ions in the PL spectra. Colour co-ordinates (X̄,Ȳ) were used for the analysis of measured photoluminescence spectra. For the optimized concentration of Sm3+ (La1-xSmxOCl with x = 0.05), the intensity parameters ( 2, 4 and 6)were determined. The trend of 6 > 4 > 2 was observed. An emission cross section and Branching ratio are found to be 3.98 × 10−22 cm2 and 59% respectively for 4G5/2 → 6H7/2 transition that makes it suitable for laser designs and application. The obtained results reveal that the LaOCl phosphor doped with samarium can be used on the screens of optical electronic systems and also is suitable for emission of reddish orange colour.
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•Lanthanum aluminate (LA) and Sm3+ doped Lanthanum aluminate (SDLA) compounds synthesized by solution combustion method using sucrose (C12H22O11) as fuel.•SDLA have shown maximum ...sensing response of 92 % in the relative humidity (RH) range 11%–97%.•The mechanism of humidity sensing is schematically represented and discussed using physisorption, chemisorption and capillary condensation.
In the present research, the enhanced room temperature operable humidity sensing response of lanthanum aluminate (LA) and (1 mol%) Sm3+ doped Lanthanum aluminate (SDLA) compound synthesized by solution combustion method using in-toxic and bio-degradable sucrose (C12H22O11) as fuel, is been discussed. Structural analysis are carried out by many analytical methods like X-ray diffraction (XRD), Scanning electron microscopy (SEM), Fourier Transform infrared (FTIR) spectroscopy. The crystallite size for the compound is about 40−60 nm as depicted by XRD studies, the SEM images and BET studies show increased porosity and specific surface area correlated with the decreased crystallite size of SDLA compared to LA. Intensified agglomeration forming the greater pores available for sensing further confirmed by Transmission electron microscopy (TEM) images. The shifting in absorption bands at tetrahedral and octahedral sites is confirmed by FTIR spectra. SDLA has shown maximum sensing response of 92 % in the relative humidity (RH) range 11%–97%. The response time for the compound was found to be 40 s and 60 s and the stability was tested for 3 months. The mechanism of humidity sensing is schematically represented using various steps of adsorption processes.
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•Scheelite-type MWO4 nanphosphors were synthesized by wet chemical approach.•CIE chromaticity diagram reveals that these nanophosphors emit intense blue luminescence.•Under UV ...illumination, we achieved 100% MB dye degradation over BaWO4 nanocatalysts within 60min.•MWO4 can be useful in removing industrial pollutants and fabricating blue component in white LEDs.
Scheelite-type MWO4 (M=Ca, Sr, and Ba) nanophosphors were synthesized by the precipitation method. All compounds crystallized in the tetragonal structure with space group I41/a (No. 88). Scherrer’s and TEM results revealed that the average crystallite size varies from 32 to 55nm. FE-SEM illustrate the spherical (CaWO4), bouquet (SrWO4), and fish (BaWO4) like morphologies. PL spectra indicate the broad emission peak maximum at 436 (CaWO4), 440 (SrWO4), and 433nm (BaWO4) under UV excitation. The calculated CIE color coordinates of MWO4 nanophosphors are close to the commercial BAM and National Television System Committee blue phosphor. The photocatalytic activities of MWO4 were investigated for the degradation of methylene blue dye under UV illumination. At pH 3, BaWO4 nanocatalyst showed 100% dye degradation within 60min. The photocatalytic activity was in the decreasing order of BaWO4>CaWO4>SrWO4 under both neutral and acidic conditions.
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