Ravindra Nath Dwivedi

IR spectra and their application for evaluating physical properties of fluorophosphate glasses

Abstract Infrared (IR) absorbance spectra in the range 500–4000 cm −1 of the glasses in the system Ba(PO3)2–MgF2–CaF2–AlF3 have been studied with increasing fluoride content. Quantitative justification for assignment of some bands has been attempted. The spectra reveal that the glass structure changes with fluoride addition from metaphosphate, (PO3−)n to P2(O,F)7 and P(O,F)4 along with the formation of Al(O,F)6,[AlF6]3− and [AlF4]−. As a result of these structural changes density (d), refractive index ne) and IR band absorption coefficient at ∼2170 cm −1 (α IR ) of the glasses vary exhibiting maxima at ∼ 36 mol% fluoride. Statistical analyses show that d and ne are correlated with αIR by linear equations. Each of these equations gives a high correlation coefficient (r) and low residual standard deviation (RSD), and may, thus, be employed for the evaluation of physical properties of fluorophosphate glasses. Physical properties of some fluorophosphate glasses of this work and the published literature have been calculated by using these equations to test their validity. The experimental properties of the glasses present a very good fit of data within 95% confidence interval of the calculated mean values. These facts indicate the suitability of this IR spectroscopic method for the determination of physical properties of fluorophosphate glasses.

UV transparency and structure of fluorophosphate glasses

Abstract Ultraviolet (UV) transparency and local structural environment of fluorophosphate glasses in the Ba(PO3)2–MgF2–CaF2–AlF3 system have been studied with increasing fluoride content (covering the whole compositional range) by infrared (IR) reflection spectroscopy (IRRS) in conjunction with 31P magic angle spinning (MAS) nuclear magnetic resonance (NMR) spectroscopy. UV cutoff of the glasses shifts towards longer wavelength with increasing fluoride up to ∼36 mol%. IRRS spectra indicate a gradual increase in nonbridging oxygens (NBOs) in this region. According to 31P MAS NMR spectra, it is due to the combined effects of gradual increase in Q1 sites and P–O–Al bridges (increase in optical basicity). Beyond ∼36 mol% fluoride content, the UV cutoff shifts towards shorter wavelength. It is attributed to decrease in NBOs or Q1 sites (decrease in optical basicity) as revealed in the IRRS and 31P MAS NMR spectra, respectively. In this region, true partial role of the metal fluorides in controlling UV transparency has been found to contribute significantly as well.

Temperature dependent luminescence characteristics of Sm3+-doped silicate glass

Abstract We report here on the optical characterisation of Sm 3+ (5 wt%): SiO 2 +Al 2 O 3 +Li 2 O+Na 2 O+MgO glass from the measurements of optical absorption spectra (at 300 K), total luminescence spectra (10–300 K) and fluorescence lifetimes (10–300 K) of the prominent emission transitions of the Sm 3+ ions. Besides its spectral properties, physical and nonlinearity characterising property parameters have also been computed to understand the optical dispersive power of this glass. By the application of Judd–Ofelt parameters ( Ω λ ) of the measured absorption spectrum, the radiative transition probability factors ( A ) and stimulated emission cross-section ( σ E p ) of the observed fluorescent levels have been analysed. Both emission intensity and measured lifetimes of the prominent luminescent transition ( 4 G 5/2 → 6 H 7/2 ) concerning Sm 3+ -glass has been showing a descending trend with the rise in temperature with N 2 -laser (337.1 nm) as the source of excitation.

Fluorescence spectra of Cu+: ZnO-B2O3-SiO2 glass

Abstract This short paper brings out an analysis on the fluorescence spectral properties of Cu + ions in a zinc borosilicate glass. A strong emission peak at 500 nm has been observed upon excitation with 296, 310 and 360 nm based on the measured excitation spectrum of this phosphorescent copper glass. This greenish blue broader luminescent transition has been due to a spin forbidden transition ( 3 E g → 1 A g ) showing significant changes in its lifetime (ms) values depending upon the excitation wavelength used.

NIR emission and upconversion luminescence spectra of Nd3+:ZnO–SiO2–B2O3 glass

Abstract Zinc-borosilicate glass containing Nd 3+ ions has been prepared to study the NIR fluorescence and the violet upconversion emission properties. NIR photoluminescence spectrum has been recorded with the 514-nm line of Ar + laser and observed three emission transitions of 4 F 3/2 → 4 I 13/2,11/2, 9/2 . The decay curve of the prominent lasing transition 4 F 3/2 → 4 I 11/2 has been measured both at 514-nm line of an Ar + laser and at 808 nm of a pulsed laser diode. A bright violet color upconversion emission has been measured from a yellow light ( 4 I 15/2 → 4 G 5/2 at 576 nm) of a xenon arc lamp.

Effect of vacuum dehydroxylation on the UV transparency and structure of metaphosphate glasses

Abstract UV cutoff of calcium metaphosphate glass shifts towards shorter wavelengths in the initial stage dehydroxylation in vacuum. IR reflection spectral study reveals that it is due to the combined effects of polymerization of the phosphate glass network and formation of small metaphosphate rings caused by the decrease in OH content. This is supported by the decrease of Q 2 sites (decrease in optical basicity) in the 31 P MAS NMR spectra. On further dehydroxylation, the shifting of UV cutoff towards longer wavelengths is attributed to the increase of Q 1 and Q 2 sites (increase in optical basicity) associated with the formation of nonbridging oxygens (NBOs). It is caused by the preferential loss of P 2 O 5 and simultaneous decrease of OH groups during exhaustive dehydroxylation for a prolonged period of melting in vacuum.

Emission properties of Eu3+ ions in ZnCl2-BaCl2-KCl glass

Abstract In this short communication, we present the results concerning the excitation and emission spectra of 1 mol% Eu 3+ -doped 50ZnCl 2 +20BaCl 2 +29KCl glass. A bright red color emission was observed under an UV source from this glass. The photoluminescence spectra have shown prominent red emission transition ( 5 D 0 → 7 F 2 ) at 610 nm along with three other weak emission transitions of 5 D 0 → 7 F 0, 1 and 3 at 580, 598 and 650 nm upon excitation with six identified excitation bands. Dependence of the emission intensities and lifetimes based on the excitation wavelengths employed has been investigated.

Effect of hydroxyl content on the physical properties of calcium metaphosphate glasses

The hydroxyl (OH) content of calcium metaphosphate glasses has been controlled in the range 50–800 ppm by melting calcium dihydrogen phosphate in air, under vacuum and with fluoride addition. Density, refractive index and glass transition temperature of the glasses increase with decrease in OH content while the coefficient of thermal expansion remains almost unchanged. With gradual decrease in OH, the UV cutoff initially shifts towards shorter and finally towards longer wavelengths. IR spectroscopic study shows that the OH groups exist exclusively in the hydrogen bonded states. Correlations of the glass properties with OH content have been explained in terms of structural rearrangement leading to the change in P-O bond length and O-P-O/P-O-P bond angles of the PO4 tetrahedral units of (PO3−)n chains. These changes are caused due to conversion of non-bridging oxygens (NBOs) of the H-bonded OH groups into bridging oxygens (BOs) during progress of dehydroxylation.

Infrared Spectroscopic Method for Estimating Physical Properties of Metaphosphate Glasses

Calcium metaphosphate glass has been dehydroxylated under vacuum and by calcium fluoride addition. The first overtone band of Vss(OPO) and/or combinational band of Vas(OPO) + vas(POP) at around 2170 cm−1 in the infrared (IR) spectra of the glasses, not originally observed in high hydroxyl (OH) containing glasses, has been found to develop gradually with the progress of dehydroxylation. The absorption coefficient of this band has been statistically correlated with density, refractive index and glass transition temperature of low OH containing glasses in the form of equations. Each of these equations has high correlation coefficient and low residual standard deviation. Thus, they have been employed for the estimation of physical properties of high OH containing glasses. The experimental values of the properties of these glasses present a good fit with the calculated mean values within 95% confidence interval. This fact confirms the validity and utility of this IR spectroscopic approach for the estimation of physical properties of calcium metaphosphate glasses.

Nucleation and crystallisation of some Na2OAl2O3SiO2 and Na2OBaOAl2O3SiO2 glasses

Abstract Na2O Al2O3 2.7 SiO2 and BaO Al2O3 2 SiO2 3(Na2O Al2O3 2 SiO2) type glass compositions with P2O5, TiO2 and CaF2 as additives were studied for nucleation and Crystallisation to obtain glass-ceramics. Structural OH groups seemed to be responsible for the initiation of crystallisation. Metastable sodium zeolite was the first phase to crystallise in the glasses. This subsequently transformed into cubic carnegieite on further heat treatment. In nephelene type composition glasses the crystalline assemblage in the glass-ceramics was nephelene and rutile. In nephelene plus celsian type composition glasses, nephelene, celsian and rutile were the major crystalline phases in the glass-ceramics.