TL, EPR and optical absorption in natural grossular crystal

Grossular is one of six members of silicate Garnet group. Two samples GI and GII have been investigated concerning their luminescence thermally stimulated (TL). EPR and optical absorption and the measurements were carried out to find out whether or not same point defects are responsible for all three properties. Although X-rays diffraction analysis has shown that both GI and GII have practically the same crystal structure of a standard grossular crystal, they presented different behavior in many aspects. The TL glow curve shape, TL response to radiation dose, the effect of annealing at high temperatures before irradiation, the dependence of UV bleaching parameters on peak temperature, all of them differ going from GI to GII. The EPR signals around g=2.0 as well as at g=4.3 and 6.0 have much larger intensity in GI than in GII. Very high temperature (>800 °C) annealing causes large increase in the bulk background absorption in GI, however, only very little in GII. In the cases of EPR and optical absorption, the difference in their behavior can be attributed to Fe³⁺ ions; however, in the TL case one cannot and the cause was not found as yet.     

Thermoluminescence and optical studies on X-irradiated terbium-doped potassium bromide crystals

This paper reports the thermoluminescence (TL) and other optical studies made on terbium-doped KBr crystals X-irradiated at room temperature. Photoluminescence studies confirm the presence of terbium ions in the KBr matrix in their trivalent form. Formation of Z₁ centres on F-bleaching of X-irradiated crystals is observed. The characteristic emission due to Tb³⁺ ions in the spectral distribution under optically stimulated emission and thermoluminescence emission confirm the participation of the Tb ions in the recombination process. TL process has been identified to be due to the thermal mobilization of electrons produced during the colouration process.     

Thermoluminescence of natural and synthetic diopside

Diopside, a natural silicate mineral of formula CaMgSi₂O₆, has been investigated concerning its thermoluminescence (TL) and electron paramagnetic resonance (EPR) properties. Glow curves and TL vs. γ-dose were obtained irradiating natural samples to additional dose varying from 50 to 10,000 Gy. Except for a 410 °C peak found in the Al-doped artificial diopside, all the other peaks grow linearly with radiation dose, but saturate beyond 1 kGy. To investigate high-temperature effect before irradiation, measurements of TL intensity in samples annealed at 500–900 °C and then irradiated to 1 kGy γ-dose were carried out. Also the TL emission spectrum has been obtained. To compare with natural diopside, a synthetic pure polycrystal was produced and further those doped with iron, aluminum and manganese were also produced.     

Thermoluminescence characterization of the irradiated minerals extracted from nopal

The mineral fraction from dehydrated nopal leaves (Opuntia ficus indica) belonging to the Cactaceae family was extracted and selected by sizes of 10 and 74 μm and exposed to ⁶⁰Co gamma radiation at different doses in the range 70 Gy–20 kGy. The glow-curves from these polyminerals show a thermoluminescence (TL) band with one very intense peak at a temperature around 150 °C and a second one emerging in the high temperature region, moving in a large zone of temperature values according to the preparation used and the level of irradiation. The XRD analysis shows a composition of both biominerals as whewellite and weddellite and a mineral fraction as anorthoclase and quartz. The main TL characteristics of the polymineral content of the nopal was analyzed, i.e. the TL response at different doses and fading during storage at room temperature. The activation energy of the traps responsible for the TL emission was also investigated and a possible continuous distribution of traps is discussed. A review of the scientific literature shows that this is the first time that a TL study on nopal ionized by irradiation has been carried out.     

Thermoluminescence and opitical absorption of BaF2 crystals

Abstract

Nominally pure and Dy-doped BaF₂ crystals were investigated concerning their optical absorption (OA) and thermoluminescence (TL) properties. Peaks at 120—150 and 200°C were observed for a heating rate of 1.7°C/s. The TL response for γ-rays and the TL emission spectra were obtained for these peaks. Except for the purest crystal, all BaF₂ crystals produced OA bands before irradiation typical of Ce³⁺ ions. After irradiation, Dy doped crystals showed bands due to Dy²⁺ ions. A nominally pure sample gave bands related to Ce²⁺ ions and photochromic centers of Ce³⁺ ions. and photochromic centres of Ce³⁺ ions. The correlation between some OA bands and TL peaks is discussed.     

High-pressure X-Ray diffraction and optical absorption studies of CsI

Static-compression data and absorption spectra for CsI have been collected to 61 GPa (610 kbar) at room temperature. The band gap closes with increasing pressure and CsI is expected to metallize at 105 (± 15) GPa. A second order phase transition to the CuAu I structure is observed at 39 (± 1) GPa. The elastic constants measured at low pressures do not predict that an elastic instability, and hence a structural distortion, would occur at elevated pressures. Similarly, an ionic pair-potential model which reproduces the properties of CsI at low pressures does not show the distortion to be stabilized at high pressures.     

Thermoluminescence emission spectra and optical bleaching of oligoclase

Thermoluminescence (TL) spectra of oligoclase samples have been recorded in the temperature range from 300 to 700 K and the wavelength range from 300 to 850 nm. Like other feldspars, oligoclase produces blue (peaking at 460 nm) and red (peaking at 765 nm) emission bands. The maximum of the red emission occurs 20 K lower than that of the band. Optical bleaching was performed at wavelengths varying from 360 to 800 nm. Bleaching of artificially irradiated oligoclase causes a decrease of the TL signal. The bleaching efficiency increases with descreasing with wavelegth. Bleaching does not only influence the height of the glow curve but also the shape. An interesting observation is that ratio of the blue and red band intensities is not affected by a bleaching procedure. No evidence has been found that bleaching influences the shape of the emission spectra. The correlation between the blue and red bands is discussed.     

Infrared reflection and optical absorption studies on SmAsO4

Polarized infrared reflection spectra from flux-grown SmAsO₄ crystals were obtained in the frequency region 100–1200 cm^-1. The observed bands were assigned and compared with those of Raman and infrared spectra. The static dielectric constants, 9.03 and 9.10, for A_2u and E_u, respectively were determined using the Lyddane-Sachs-Teller (LST) relation. Optical absorption measurements suggest that a suitably high dosage of X-ray irradiation increases the background absorption, indicating an increase in the energy band gap in the lower wavelength region.     

Thermoluminescence and ESR of γ-ray and pile-irradiated natural barite

Thermoluminescence (TL) and electron spin resonance (ESR) studies of γ-ray and pile-irradiated natural barite have led to the identification of centres which act as electron or hole traps. Intense pile irradiation seems to help the formation of the S₂O₃-radical. The presence of cation vacancies, as indicated by TL glow curves, makes pile-irradiated (>10¹⁸ n cm^-2 samples “immune” to further γ-irradiations as far as TL and ESR are concerned.     

On the synthesis and optical absorption studies of nano-size magnesium oxide powder

Magnesium oxide (MgO) nano-size powder is synthesized using magnesium nitrate hexahydrate and oxalic acid as precursors with ethanol as a solvent. The process involves gel formation, drying at 100 °C for 24 h to form magnesium oxalate dihydrate [α-MgC₂O₄·2H₂O] and its decomposition at 500, 600, 800, and 1000 °C for 2 h to yield MgO powder (average crystallite size ∼6.5-73.5 nm). The sol-gel products at various stages of synthesis are characterized for their thermal behaviour, phase, microstructure, optical absorption, and presence of hydroxyl and other groups like OCO, CO, C-C, etc. MgO powder is shown to possess an f.c.c. (NaCl-type) structure with lattice parameter increasing with decrease in crystallite size (t_av); typical value being ∼4.222(2) Å for t_av∼6.5 nm as against the bulk value of 4.211 Å. Infrared absorption has shown MgO to be highly reactive with water. Also, a variety of F- and M-defect centres found in MgO produce energy levels within the band gap (7.8 eV), which make it attractive for application in plasma displays for increasing secondary electron emission and reducing flickering effects. The possible application of the intermediate sol-gel products, viz., α-MgC₂O₄·2H₂O and anhydrous magnesium oxalate (MgC₂O₄) in understanding the plants and ESR dosimetry, respectively, has also been suggested.     

EPR and optical absorption studies of V O ions in L-asparagine monohydrate

Electron paramagnetic resonance (EPR) studies of V O²⁺ ions in L-asparagine monohydrate single crystals are reported at room temperature. It is found that the V O²⁺ ion takes up an interstitial site. The angular variations of the EPR spectra in three mutually perpendicular planes are used to determine the principal g and A values and their direction cosines. The values of g and A parameters are: g_x=1.9011, g_y=2.1008, g_z=1.9891 and A_x=100, A_y=78, A_z=126 (×10⁻⁴) cm⁻¹. The optical absorption spectrum of V O²⁺ ions in L-asparagine monohydrate is also studied at room temperature. The band positions are calculated using the energy expressions and compared with the observed band positions to confirm the transitions. The best-fit values of the crystal field (Dq) and tetragonal (Ds and Dt) parameters are evaluated from the observed band positions.     

EPR and optical absorption studies of X-irradiated cobalt doped sodium chloride crystals

Sodium chloride crystals containing small concentrations of cobalt (< 10 ppm) do not show any EPR line. A thick block of crystal containing ～25 ppm of Co showed two partially resolved lines, with approximate g-values 2.036 and 2.011. These g-values are not close to those of Co⁺⁺ (4.0 to 4.5) in other crystals. On X-irradiation, pure NaCl crystals show a complex EPR spectrum. X-irradiated Co doped NaCl crystals showed an EPR line superimposed on the complex EPR spectrum. Cobalt doped highly pure crystals, on X-irradiation, showed an EPR line superimposed on the F center EPR line. The g-value of the former is 2.049±0.002 and half width is 62±3 gauss. These results combined with those of dielectric loss and optical studies show that X-irradiation of Co doped crystals produces new centers, labelled as S centers, which produce a dielectric loss peak, a decrease in electrical conductivity, an optical band at 210 nm and the EPR line. Possible models of the S centers are discussed.     

EPR and optical absorption studies of Fe ions in sodium borophosphate glasses

Electron paramagnetic resonance (EPR) and optical absorption spectral investigations have been carried out on Fe³⁺ ions doped sodium borophosphate glasses (NaH₂PO₄-B₂O₃-Fe₂O₃). The EPR spectra exhibit resonance signals with effective g values at g=2.02, g=4.2 and g=6.4. The resonance signal at g=4.2 is due to isolated Fe³⁺ ions in site with rhombic symmetry whereas the g=2.02 resonance is due to Fe³⁺ ions coupled by exchange interaction in a distorted octahedral environment. The EPR spectra at different temperatures (123-295 K) have also been studied. The intensity of the resonance signals decreases with increase in temperature whereas linewidth is found to be independent of temperature. The paramagnetic susceptibility (χ) was calculated from the EPR data at various temperatures and the Curie constant (C) and paramagnetic Curie temperature (θ_p) have been evaluated from the 1/χ versus T graph. The optical absorption spectrum exhibits bands characteristic of Fe³⁺ ions in octahedral symmetry. The crystal field parameter (Dq) and the Racah interelectronic repulsion parameters (B and C) have also been evaluated and discussed.     

Nonlinear optical absorption studies of an organo-metallic complex by Z-scan technique

An organo-metallic complex, [(CH₃)₄N][Ni(dmit)₂] (dmit²⁻ = (1,3-dithiole-2-thione-4,5-dithiolate), abbreviated as MeNi, is synthesized. The nonlinear optical absorption properties of MeNi dissolved in acetone have been studied using the open-aperture Z-scan technique with 40 ps pulse width at 1064 nm and 1 ns, 15 ns pulse width at 1053 nm, respectively. Strong saturable absorption has been found when the sample solution is irradiated by 40 ps and 1 ns laser pulses. While irradiated with 15 ns laser pulse, a stronger reverse saturable absorption has been found. The nonlinear optical absorption coefficients are −1.03 × 10⁻¹¹ m/W, −1.85 × 10⁻¹¹ m/W and 3.84 × 10⁻¹⁰ m/W, respectively. The mechanism responsible for the difference between the results is analyzed. All the results suggest that this material may be a promising candidate for the application to laser pulse compression in the near-infrared waveband.     

EPR and optical absorption studies on VO ions in zinc lactate trihydrate

EPR and optical absorption studies of VO²⁺-doped zinc lactate trihydrate single crystals are done at room temperature. The EPR spectra of VO²⁺ are characteristic of tetragonally compressed octahedral site. The angular variation of the EPR spectra shows single site occupying interstitial position in the lattice. The spin Hamiltonian parameters are evaluated as g_x=1.9771, g_y=2.0229, g_z=1.9236 and A_x=76, A_y=104, A_z=197 (×10⁻⁴) cm⁻¹. Using these parameters and optical absorption data various bonding parameters are determined and the nature of bonding in the complex is discussed.     

Thermoluminescence and absorption spectra of CdSe quantum dot-doped glass irradiated by X-rays

Thermally stimulated luminescence (TSL) of aluminoborosilicate glass doped with CdSe nanoparticles (28 and 47 Å) has been studied after exposure to ionizing radiation; the intense TSL peaks were observed at temperatures 150 and 85 °C, respectively. The optical absorption spectra, as well as TSL of the irradiated samples containing CuBr nanoparticles (44 Å) were also measured. In the case of CuBr, TSL was observed neither before nor after irradiation. The dependence of TSL intensity on irradiation time indicates that glass activated by CdSe nanoparticles shows promise as a dosimetric material.     

EPR and optical absorption studies of vanadyl impurity in lithium hydrogen oxalate single crystal

Electron paramagnetic resonance (EPR) and optical absorption studies of vanadyl ions in lithium hydrogen oxalate monohydrate single crystal and powder are reported at room temperature. Single crystal rotations in each of the three mutually orthogonal crystalline planes, $a{b}^1$, $b^1{c}^1$ and $a{c}^1$ indicate four different vanadyl complexes. The detailed investigation of EPR spectra indicates that one of the VO^{2 +} sites (the intense one) may enter the lattice substitutionally and the other three occupy the interstitial positions. From the angular variation, the spin Hamiltonian parameters are evaluated and discussed. The optical absorption spectrum shows four bands. From the optical and EPR data, various bonding parameters are determined and the nature of bonding in the crystal is discussed.