Demystification of luminescence properties and the near imperceptible thermal quenching of Sm3+-doped tungstate phosphors.

Ultra-high thermally stable Ca2MgWO6:xSm3+ (x = 0.5, 0.75, 1, 1.25, and 1.5 mol%) double perovskite phosphors were synthesized through solid-state reaction method. Product formation was confirmed by comparing the X-ray diffraction (XRD) patterns of the phosphors with the standard reference file. The structural, morphological, thermal, and optical properties of the prepared phosphor were examined in detail using XRD, Fourier transform infrared spectra, scanning electron microscopy, diffused reflectance spectra, thermogravimetric analysis (TGA), photoluminescence emission, and temperature-dependent PLE (TDPL). It was seen that the phosphor exhibited emission in the reddish region for the near-ultraviolet excitation with moderate Colour Rendering Index values and high colour purity. The optimized phosphor (x = 1.25 mol%) was found to possess a direct optical band gap of 3.31 eV. TGA studies showed the astonishing thermal stability of the optimized phosphor. Additionally, near-zero thermal quenching was seen in TDPL due to elevated phonon-assisted radiative transition. Furthermore, the anti-Stokes and Stokes emission peaks were found to be sensitive toward the temperature change and followed a Boltzmann-type distribution. All these marked properties will make the prepared phosphors a suitable candidate for multifield applications and a fascinating material for further development.

Thermoluminescence properties of copper-doped TiO2 nanoparticles synthesised using co-precipitation method for high-dose gamma dosimetry.

In this work, copper (Cu)-doped titanium dioxide (TiO2) nanoparticles were prepared by co-precipitation. For studying the morphological properties, the copper doped titanium dioxide (TiO2:Cu) nanocrystalline structures were characterised through powder X-ray diffraction and field emission scanning electron microscopy. The prepared TiO2:Cu nanoparticles were annealed at two temperatures, namely, copper doped titanium dioxide annealed at 723 K temperayure (TC1) and copper doped titanium dioxide annealed at 1073 K temperayure (TC2). The annealed samples were exposed to gamma radiation of 10-Gy-to-25-kGy doses. Thermoluminescence and dosimetric properties were evaluated using a thermoluminescent dosemeter reader. The glow curves of the TiO2:Cu nanoparticles were analysed. The thermoluminescence (TL) response of samples exhibited good linearity between 100 Gy and 10 kGy with high sensitivity of 1755.25 (TC1) and 5587.06 (TC2) counts g-1Gy-1 and a minimum detectable dose of 2.9666 Gy (TC1) and 0.4892 Gy (TC2). The fading of signals was observed by 12% for TC1 and 10% for TC2 samples after a week of storage.

Thermoluminescence dosimetric attributes of Yb3+ -doped BaO-ZnO-LiF-B2 O3 glass material after Er3+ co-doping.

Motivated by our previous study on Sm3+ ions as thermoluminescence (TL) sensitizers to the BaO-ZnO-LiF-B2 O3 -Yb2 O3 glass system, in the current study we examined the effect of Er3+ ion co-doping on the TL characteristics of this glass system. The 4f-4f electronic transitions of the Er3+ and Yb3+ ions were confirmed via the optical absorption spectrum. Notably, the use of Yb3+ -Er3+ ions failed to improve the TL intensity, sensitivity, and trap density. However, they enabled the glass system to function as an activator-quencher system. The linearity range and effective atomic number remained unaffected after co-doping. In addition, the problem of anomalous fading caused a remnant signal of just 58% after a week of storage of the Yb3+ monodoped glass. This was resolved by the optimum co-doping of Er3+ ions to achieve an 89% signal. The co-doping of Er3+ ions to the BaO-ZnO-LiF-B2 O3 -Yb2 O3 glass system regulated its thermal stability and therefore supplemented its potential for radiation monitoring in food processing and retrospective dosimetry.

Influence of Bi2O3 on Mechanical Properties and Radiation-Shielding Performance of Lithium Zinc Bismuth Silicate Glass System Using Phys-X Software.

We analyzed the mechanical properties and radiation-shielding performance of a lithium zinc bismuth silicate glass system. The composition of these glasses is 20ZnO-30Li2O-(50-x)SiO2-xBi2O3 (x varies between 10 and 40 mol%). The mechanical properties of the investigated glass system, such as Young's modulus (E), bulk modulus (K), shear modulus (S), and longitudinal modulus (L), were determined using the Makishima-Mackenzie model. The elastic moduli gradually decreased with the addition of Bi2O3. E decreased from 46 to 31 GPa, K decreased from 27 to 14 GPa, S decreased from 19 to 14 GPa, and L decreased from 52 to 32 GPa as Bi2O3 was substituted for SiO2. The mass attenuation coefficient (MAC) was investigated at energies between 0.284 and 1.33 MeV to understand the radiation-shielding performance of the glasses. The MAC value increased when SiO2 was replaced by Bi2O3. We found that the effect of Bi2O3 on MAC values was noticeably stronger at energies of 0.284 and 0.347 MeV, while the effect of Bi2O3 on MAC values became weaker as energy increased. The linear attenuation coefficient (LAC) results demonstrated that if the samples were exposed to low-energy photons, the glass could prevent the penetration of photons, and thus, the glass samples were effective in radiation protection. The LAC values for the lowest- and highest-density samples changed from 0.998 to 1.976 cm-1 (at 0.284 MeV) and from 0.286 to 0.424 cm-1 (at 0.826 MeV). According to the radiation-shielding results, the thick, high-density glass sample has special and distinctive shielding properties.

Structural and Optical Modifications in the BaO-ZnO-LiF-B2O3-Yb2O3 Glass System after γ-Irradiation.

A Yb3+-doped borate glass system was examined for the structural and optical modifications after γ-irradiation. Among the studied 10BaO-20ZnO-20LiF-(50-x)B2O3-xYb2O3 (x = 0.1, 0.5, 0.7, and 1.0 mol%) glasses, the 10BaO-20ZnO-20LiF-49.9B2O3-0.1Yb2O3 glass showed the highest thermoluminescence intensity, trap density, and trap depth. The glass was irradiated with the optimum γ-dose of 1 kGy towards the analysis of radiation-induced defects. The amorphous nature was preserved before and after irradiation. The glass density slightly increased after irradiation. The structural rearrangement was evident from the Fourier transform infrared spectroscopy by the appearance and disappearance of some bonds after γ-irradiation. The transformation of [BO4] units into [BO3] units and non-bridging oxygens was deduced. The color of the glass darkened after irradiation and the optical absorption intensity enhanced between 250 and 700 nm. The optical bandgap reduced and Urbach energy increased upon γ-dose exposure. The electron spin resonance of the irradiated glass exhibited two signals at g = 2.0167 and g = 1.9938, corresponding to the non-bridging oxygen hole center and Boron E'-center, respectively.

Composition dependent structural and optical properties of PbF2-TeO2-B2O3-Eu2O3 glasses.

Boric oxide based quaternary glasses in the system PbF2-TeO2-B2O3-Eu2O3 have been prepared by melt quenching technique. Density, molar volume, FTIR, UV-Vis techniques were used to probe the structural modifications with incorporation of europium ions in the glass network. An increase in glass density & decrease in molar volume (Vm) values proved the structural changes occurring in coordination of boron atom [conversion of BO3 units to BO4]. This resulted in the increase of the compaction of the prepared glasses with increase in Eu2O3 contents. The amorphous natures of the samples were ascertained by XRD and metallization criterion (M) studies. XPS study showed the values of core-level binding energy [O1s, Eu3d, Eu4d, Te3d, Te4d, Pd4f, Pb5d, O1s, and F1s] of (PbF2-TeO2-B2O3-Eu2O3) the glass matrix. The frequency and temperature dependence of dielectric properties of present glasses were investigated in the frequency range of 1 Hz-10 MHz and temperature range of 313-773K. The study of dielectric measurements proved good insulating and thermal stability of the prepared glasses. At room temperature, dielectric loss [tanδ] values were negligibly small for prepared glasses and increased with increase in temperature. FTIR spectroscopy results were in good agreement with optical band energy gap, density, molar volume and hardness values revealing network modifications caused by europium ions in the glass structure.

Photoacoustic spectroscopy of ovarian normal, benign, and malignant tissues: a pilot study.

Photoacoustic spectra of normal, benign, and malignant ovarian tissues are recorded using 325-nm pulsed laser excitation in vitro. A total of 102 (34 normal, 38 benign, and 30 malignant) spectra are obtained from 22 samples belonging to normal, benign, and malignant subjects. Applying multi-algorithm approach, comprised of methods such as, principal component analysis (PCA) based k-nearest neighbor (k-NN) analysis, artificial neural network (ANN) analysis, and support vector machine (SVM) analysis, classification of the data has been carried out. For PCA, first the calibration set is formed by pooling 45 spectra, 15 belonging to each of pathologically certified normal, benign, and malignant samples. PCA is then performed on the data matrix, comprised of the six spectral features extracted from each of 45 calibration samples, and three principal components (PCs) containing maximum diagnostic information are selected. The scores of the selected PCs are used to train the k-NN, ANN, and SVM classifiers. The ANN used is a classical multilayer feed forward network with back propagation algorithm for its training. For k-NN, the Euclidean distance based algorithm is used and for SVM, one-versus-rest multiclass kernel-radial basis function is used. The performance evaluation of the classification results are obtained by calculating statistical parameters like specificity and sensitivity. ANN and k-NN techniques showed identical performance with specificity and sensitivity values of 100 and 86.76%, whereas SVM had these values at 100 and 80.18%, respectively. In order to determine the relative diagnostic performance of the techniques, receiver operating characteristics analysis is also performed.

Autofluorescence of osteoporotic mouse femur bones: a pilot study.

OBJECTIVE: The objective of this study was to evaluate the efficacy of laser-induced fluorescence (LIF) in combination with principal component analysis (PCA) to characterize osteoporotic conditions induced by ovariectomy (OVX) in mice. BACKGROUND DATA: The dual energy X-ray absorptiometry is the gold standard methodology routinely used to diagnose osteoporosis. In recent years, the use of LIF to characterize human disease and to aid in diagnosis has shown great promise. However, this technique has not been much exploited for monitoring osteoporosis. MATERIALS AND METHODS: Swiss albino mice were sacrificed 2, 3, 4, and 5 wk after OVX and their femur bones were excised. The same protocol was used for age-matched female controls (no OVX). The LIF spectra from different regions of the bones were recorded and compared using PCA. RESULTS: A significant change in the fluorescence pattern of osteoporotic bones compared with the control was indicated by PCA match/no-match analysis. A region-wise PCA match/no-match analysis of the spectral changes against respective region calibration sets indicated more no-matches in the fifth week bones compared with the others. Further, the spectral differences were more prominent in the proximal and distal parts of the bones. In addition to the PCA, Gaussian curve fitting was also performed on control, third week, and fifth week bone spectra to identify different spectral components in them. CONCLUSION: This preliminary study using fluorescence spectroscopy in combination with PCA clearly demonstrated osteoporotic changes in mouse femur bones at different time points after OVX, suggesting possible human applications.

Principal component analysis (PCA)-based k-nearest neighbor (k-NN) analysis of colonic mucosal tissue fluorescence spectra.

OBJECTIVE: The objective of this study was to verify the suitability of principal component analysis (PCA)-based k-nearest neighbor (k-NN) analysis for discriminating normal and malignant autofluorescence spectra of colonic mucosal tissues. BACKGROUND DATA: Autofluorescence spectroscopy, a noninvasive technique, has high specificity and sensitivity for discrimination of diseased and nondiseased colonic tissues. Previously, we assessed the efficacy of the technique on colonic data using PCA Match/No match and Artificial Neural Networks (ANNs) analyses. To improve the classification reliability, the present work was conducted using PCA-based k-NN analysis and was compared with previously obtained results. METHODS: A total of 115 fluorescence spectra (69 normal and 46 malignant) were recorded from 13 normal and 10 malignant colonic tissues with 325 nm pulsed laser excitation in the spectral region 350-600 nm in vitro. We applied PCA to extract the relevant information from the spectra and used a nonparametric k-NN analysis for classification. RESULTS: The normal and malignant spectra showed large variations in shape and intensity. Statistically significant differences were found between normal and malignant classes. The performance of the analysis was evaluated by calculating the statistical parameters specificity and sensitivity, which were found to be 100% and 91.3%, respectively. CONCLUSION: The results obtained in this study showed good discrimination between normal and malignant conditions using PCA-based k-NN analysis.

Autofluorescence of normal, benign, and malignant ovarian tissues: a pilot study.

OBJECTIVE: The objective of this study is to evaluate the efficacy of laser-induced fluorescence (LIF) data obtained at 325-nm pulsed laser excitation for the discrimination of normal, benign, and malignant ovarian tissues. BACKGROUND DATA: Several studies have reported that the autofluorescence technique has a high specificity and sensitivity for discrimination between diseased and non-diseased tissues of various cancers, and also has the advantages of being non-invasive and producing a real-time diagnosis. When using this technique on ovarian tissues in most of the previously reported studies, multivariate statistical tools were used and classification analyses were carried out. MATERIALS AND METHODS: Autofluorescence spectra of normal, benign, and malignant ovarian tissues were recorded with 325-nm pulsed laser excitation in the spectral region from 350-600 nm in vitro. The spectral analysis for discrimination between the different types of tissues was carried out using principal component analysis (PCA)-based non-parametric k-nearest neighbor (k-NN) analysis. RESULTS: A total of 97 (34 normal, 33 benign, and 30 malignant) spectra were obtained from 22 subjects with normal, benign, and malignant tissues. The discrimination analysis of data using a PCA-based k-NN algorithm showed very good discrimination. The performance of the analysis was evaluated by calculating statistical parameters, specificity, sensitivity, and accuracy and were found to be 100%, 90.90%, and 94.2%, respectively. CONCLUSION: The results show that the discrimination of normal, benign, and malignant ovarian conditions can be achieved quite successfully using LIF.

Dynamics of L-tryptophan in aqueous solution by simultaneous laser induced fluorescence (LIF) and photoacoustic spectroscopy (PAS).

An experimental system for measuring simultaneously photoacoustic (PA) and fluorescence signals is described. The simultaneous measurement of laser induced fluorescence and photoacoustic signals provide a suitable method for the study of different quenching phenomena occurring in fluorescent systems. In this paper we report tryptophan solvation dynamics in water using fluorescence and photoacoustic spectra recorded simultaneously by photoacoustic and fluorescence signals as functions of concentration, indicate that quantum yield is maximum at low concentrations. Also, the energy lost in the fluorescence path of tryptophan, due to different quenching phenomena like self quenching, Resonance energy transfer (RET), solvation relaxation, etc. is clearly seen from the photoacoustic signal intensity which increases as the fluorescence intensity decreases.

Optical pathology using oral tissue fluorescence spectra: classification by principal component analysis and k-means nearest neighbor analysis.

The spectral analysis and classification for discrimination of pulsed laser-induced autofluorescence spectra of pathologically certified normal, premalignant, and malignant oral tissues recorded at a 325-nm excitation are carried out using MATLAB@R6-based principal component analysis (PCA) and k-means nearest neighbor (k-NN) analysis separately on the same set of spectral data. Six features such as mean, median, maximum intensity, energy, spectral residuals, and standard deviation are extracted from each spectrum of the 60 training samples (spectra) belonging to the normal, premalignant, and malignant groups and they are used to perform PCA on the reference database. Standard calibration models of normal, premalignant, and malignant samples are made using cluster analysis. We show that a feature vector of length 6 could be reduced to three components using the PCA technique. After performing PCA on the feature space, the first three principal component (PC) scores, which contain all the diagnostic information, are retained and the remaining scores containing only noise are discarded. The new feature space is thus constructed using three PC scores only and is used as input database for the k-NN classification. Using this transformed feature space, the centroids for normal, premalignant, and malignant samples are computed and the efficient classification for different classes of oral samples is achieved. A performance evaluation of k-NN classification results is made by calculating the statistical parameters specificity, sensitivity, and accuracy and they are found to be 100, 94.5, and 96.17%, respectively.