Fracto‐mechanoluminescence and thermoluminescence properties of UV and γ‐irradiated Ca2Al2SiO7:Ce3+ phosphor

Ce³⁺‐doped calcium aluminosilicate phosphor was prepared by a combustion‐assisted method at an initiating temperature of 600°C. Structural characterization was carried out using X‐ray diffraction (XRD) and scanning electron microscopy (SEM). The absorption spectra of Ca₂Al₂SiO₇:Ce³⁺ showed an absorption edge at 230 nm. The optical characterization of Ca₂Al₂SiO₇:Ce³⁺ phosphor was investigated in a fracto‐mechanoluminescence (FML) and thermoluminescence (TL) study. The peak of ML intensity increased as the height of impact of the moving piston increased. The TL intensity of Ca₂Al₂SiO₇:Ce³⁺ was recorded for different exposure times of UV and γ‐irradiation and it was observed that TL intensity was maximum for a UV irradiation time of 30 min and for a γ‐dose of 1180 Gy. The TL intensity had three peaks for UV irradiation at temperatures 82°C, 125°C and 203°C. Also the TL intensity had a single peak at 152°C for γ‐irradiation. The TL and ML emission spectra of Ca₂Al₂SiO₇:Ce³⁺ phosphor showed maximum emission at 400 nm. The possible mechanisms involved in the TL and ML processes of the Ca₂Al₂SiO₇:Ce³⁺ phosphor are also explained. Copyright © 2015 John Wiley & Sons, Ltd.     

Ca2Al2SiO7:Ce3+ phosphors for mechanoluminescence dosimetry

A series of Ce³⁺ ion single‐doped Ca₂Al₂SiO₇ phosphors was synthesized by a combustion‐assisted method at an initiating temperature of 600 °C. The samples were annealed at 1100 °C for 3 h and their X‐ray diffraction patterns confirmed a tetragonal structure. The phase structure, particle size, surface morphology and elemental analysis were analyzed using X‐ray diffraction (XRD), transmission electron microscope (TEM), scanning electron microscopy (SEM) and energy dispersive X‐ray (EDX) spectroscopy techniques. Thermoluminescence (TL) intensity increased with increase in ultraviolet (UV) light exposure time up to 15 min. With further increase in the UV irradiation time the TL intensity decreases. The increase in TL intensity indicates that trap concentration increased with UV exposure time. A broad peak at 121 °C suggested the existence of a trapping level. The peak of mechanoluminescence (ML) intensity versus time curve increased linearly with increasing impact velocity of the moving piston. Mechanoluminescence intensity increased with increase in UV irradiation time up to 15 min. Under UV‐irradiation excitation, the TL and ML emission spectra of Ca₂Al₂SiO₇:Ce³⁺ phosphor showed the characteristic emission of Ce³⁺ peaking at 400 nm (UV–violet) and originating from the Ce³⁺ transitions of 5d‐4f (²F_5/2 and ²F_7/2). The photoluminescence (PL) emission spectra for Ca₂Al₂SiO₇:Ce³⁺ were similar to the ML/TL emission spectra. The mechanism of ML excitation and the suitability of the Ca₂Al₂SiO₇:Ce³⁺phosphor for radiation dosimetry are discussed. Copyright © 2016 John Wiley & Sons, Ltd.     

Photo and thermoluminescence of KMgSO4F: Ce and :Mn phosphors

KMgSO₄F:Ce and KMgSO₄F:Mn phosphors were prepared by a wet chemical method and studied for their photoluminescence (PL) and thermoluminescence (TL) characteristics. PL emission of KMgSO₄F:Ce peaked at around 440 nm for the excitation at 377 nm due to 5d → 4f transition, while KMgSO₄F:Mn had a peak at 540 nm for an excitation at 363 nm and 247 nm due to ⁴T_1g → ⁶A_1g transition. The phosphors also showed good thermoluminescence characteristics when they were exposed to γ‐rays at a 5 Gy dose at the rate of 0.36 kGyh^?1. KMgSO₄F:Ce exhibited a single thermoluminescence (TL) peak at around 167 °C and KMgSO₄F:Mn also exhibited a single TL peak at around 177 °C. Possible trapping parameters such as order of kinetics (b), the geometrical factor (μ_g), the frequency factor (s) and the activation energy were also evaluated by Chen's half width method. This article discusses fundamental PL and TL characteristics in inorganic fluoride material activated by Ce³⁺ and Mn²⁺ ions and prepared by a wet chemical method. Copyright © 2014 John Wiley & Sons, Ltd.     

Solvation Modulation and Reversible SiO2-Enriched Interphase Enabled by Deep Eutectic Sol Electrolytes for Low-Temperature Zinc Metal Batteries

Zinc metal batteries (ZMBs) hold great promise for large-scale energy storage in renewable solar and wind farms. However, their widespread application is hindered by poor stability and unsatisfactory low-temperature performance, attributed to issues such as dendrite formation, strong Zn²⁺-H₂O coordination, and electrolyte freezing. Herein, a deep eutectic sol electrolyte (DESE) is proposed by mixing SiO₂ nanoparticles with a solution composed of 1,3-dioxolane (DOL) and Zn(ClO₄)₂·6H₂O for stable low-temperature ZMBs. By substituting the strong Zn²⁺- H₂O coordination with favorable Zn²⁺-DOL coordination, the DESE exhibits exceptional antifreezing capability at temperatures beyond −40 °C. The formation of Si-O-Zn²⁺ bond near SiO₂ nanoparticles further improves the low-temperature performance of the DESE by decreasing Zn²⁺ desolvation energy. Moreover, the SiO₂ nanoparticles co-plating/co-stripping with Zn metal, forming a reversible and homogeneous SiO₂-enriched interphase to protect the Zn anode from dendrite growth and interfacial side reactions. Remarkably, the DESE-based ZMB full cells exhibit significantly prolonged cycle life of 8000 cycles at 1 A g⁻¹ at 25 °C and 700 cycles at 0.2 A g⁻¹ at -40 °C. This work provides a promising strategy to design advanced electrolytes for practical low-temperature ZMBs.     

Effect of different temperatures to remove reduction gas on the photoluminescence properties of Eu‐doped Li2(Ba1‐xSrx)SiO4 phosphors

In this study, Eu‐doped Li₂(Ba_1‐xSr_x)SiO₄ powders (x = 0, 0.2, 0.4, and 0.6) were synthesized at 850°C in a reduction atmosphere (5% H₂ + 95% N₂) for a duration of 1 h using a solid‐state reaction method. The reduction atmosphere was infused as the synthesis temperature reached 850°C, and was removed as the temperature dropped to 800–500°C. Li₂(Ba_1‐xSr_x)SiO₄ (or Li₂BaSiO₄), (Ba,Sr)₂SiO₄ (or BaSiO₄), and Li₄SiO₄ phases co‐existed in the synthesized Eu‐doped Li₂(Ba_1‐xSr_x)SiO₄ powders. A new finding was that the reduction atmosphere removing (RAR) temperature of the Li₂(Ba_1‐xSr_x)SiO₄ phosphors had a large effect on their photoluminescence excitation (PLE) and PL properties. Except for the 800°C‐RAR‐treated Li₂BaSiO₄ phosphor, PLE spectra of all other Li₂(Ba_1‐xSr_x)SiO₄ phosphors had one broad emission band with two emission peaks centred at ~242 and ~283 nm; these PL spectra had one broad emission band with one emission peak centred at 502–514 nm. We showed that the 800°C‐RAR‐treated Li₂BaSiO₄ phosphor emitted a red light and all other Li₂(Ba_1‐xSr_x)SiO₄ phosphors emitted a green light. Reasons for these results are discussed thoroughly.     

Thermoluminescence characterization of Ag‐doped Li2B4O7 single crystal materials

In this study, the thermoluminescence (TL) characteristics of Ag‐doped and undoped lithium tetraborate (Li₂B₄O₇, LTB) materials, grown using the Czochralski method, were reported. The TL properties of LTB:Ag, such as glow curve structure, dose response, fading and reproducibility, were investigated. The glow curve of the Li₂B₄O₇:Ag single crystal consists of four peaks located at approximately 75, 130, 190 and 275°C; in undoped LTB, the single crystal shows a broad glow curve with peaks at 65, 90, 125, 160 and 190°C using a heating rate of 5°C/s in the 50–350°C temperature region. The high temperature peak of Ag‐doped sample at 275°C has a nonlinear dose response within the range from 33 mGy to 9 Gy. There is a linear response in the range of 33–800 mGy; after which, a sublinear region appears up to 9 Gy for Ag‐doped LTB single crystal. For undoped single crystal, the dose response is supralinear for low doses and linear for the region between 1 and 9 Gy. The thermal fading ratio of the undoped material is almost 60% for the high temperature peak after 7 days. Ag‐doped LTB single crystal exhibits different behaviour over a period of 7 days.     

Mechanoluminescence,thermoluminescence, photoluminescence studies on Ca3Y2Si3O12:RE3+ (RE3+ = Dy3+and Eu3+) phosphors

Dy³⁺ and Eu³⁺ activated Ca₃Y₂Si₃O₁₂ phosphors were synthesized by the solid‐state synthesis method. The phosphors were characterized by X‐ray diffraction (XRD), mechanoluminescence (ML), thermoluminescence (TL) and photoluminescence (PL) to determine structure and luminescence. For ML glow curves, only one peak was observed, as only one type of luminescence centre was formed during irradiation. The Ca₃Y₂Si₃O₁₂:Dy³⁺ TL glow curve showed a single peak at 151.55°C and the Ca₃Y₂Si₃O₁₂:Eu³⁺ TL glow curve peaked at 323°C with a small peak at 192°C, indicating that two types of traps were activated. The trapping parameters for both the samples were calculated using Chen's peak shape method. Dy³⁺‐activated Ca₃Y₂Si₃O₁₂ showed emission at 482 and 574 nm when excited by a 351 nm excitation wavelength, whereas the Eu³⁺‐activated Ca₃Y₂Si₃O₁₂ phosphor PL emission spectra showed emission peaks at 613 nm, 591 nm, 580 nm when excited at 395 nm wavelength. When excited at 466 nm, prominent emission peaks were observed at their respective positions with very slight shifts. Copyright © 2015 John Wiley & Sons, Ltd.     

Thermoluminescence emission on lead oxychloroborate glasses under UV exposure

Glassy materials were prepared using two different systems: 50B₂O₃ – (50 ? x)PbO ? xPbCl_2, with x = 0, 2 and 5 in mol % (System BPCl‐I) and 50BO_1.5 – (50 ? x)PbO ? xPbCl₂ with x = 0, 2, 5 and 7 in cationic % (System BPCl‐II). Structural and optical characterization showed that PbCl when substituted for PbO changed the structure of the glass network by replacing nonbridging oxygens for chlorine ions. This substitution also caused a change in the number of defects responsible for thermoluminescence (TL) emission (electrons and hole trap centres). Thermoluminescence emissions were observed for the first time in lead oxychloroborate glasses after exposure to UV radiation. Sample BPCl‐I‐2 (x = 2 from System I) demonstrated better TL emission compared with other glass samples. One intense peak in the glow curve, centred at ~122°C followed by a shoulder at ~180°C, was highly sensitive to UV radiation. There were also good linear responses at dose range ~0.4 to ~2 J/cm² for the first peak (low temperature) and ~0.4 to ~4 J/cm² for the second peak (high temperature).     

Effect of pH on the thermoluminescence of spinach chloroplasts in the presence and absence of Photosystem II inhibitors

The glow curve of chloroplasts excited by continuous light of high intensity (500 W · m⁻²) at pH 7.5 during cooling from +2 to −80°C consisted of seven bands appearing at about −30°C (TL₋₃₀), −15°C (TL₋₁₀), +10°C (TL₊₁₀), +30°C (TL₊₃₀), +50°C (TL₊₅₀), +65°C (TL₊₆₅) and +85°C (TL₊₈₀), in which TL stands for thermoluminescence. In the pH range from 5.5 to 9.0 the peak positions of the TL₋₃₀, TL₋₁₀, TL₊₅₀, TL₊₆₅ and TL₊₈₀ bands were independent of pH. On the other hand the peak positions of the TL₊₁₀ and TL₊₃₀ bands were gradually shifted from +25 to −5°C and from +20 to +40°C, respectively, as the pH was decreased from 9.0 to 5.5. The same pH-induced shift (from +25 to −5°C) was observed for the TL₊₁₀ band when electron transport was inhibited by DCMU. In dinoseb-treated chloroplasts the peak position of the main thermoluminescence band also exhibited pH dependency, and shifted from +20 to −20°C upon lowering the pH from 9.0 to 5.5. After the water-splitting system had been inactivated by Tris or NH₂OH treatment no pH-induced shifts were observed in the peak positions of the thermoluminescence bands of DCMU and dinoseb-treated chloroplasts. The results suggest that the effect of pH on the thermoluminescence of untreated and inhibitor-treated chloroplasts is associated with protonation/deprotonation reactions occurring at the donor and acceptor sides of Photosystem II during the S₁ → S₂ transition of the water-splitting system.     

Thermoluminescence properties of gamma‐irradiated nano‐structure hydroxyapatite

The suitability of nano‐structured hydroxyapatite (HAP) for use as a thermoluminescence dosimeter was investigated. HAP samples were synthesized using a hydrolysis method. The formation of nanoparticles was confirmed by X‐ray diffraction and average particle size was estimated to be ~30 nm. The glow curve exhibited a peak centered at around 200 °C. The additive dose method was applied and this showed that the thermoluminescence (TL) glow curves follow first‐order kinetics due to the non‐shifting nature of T_m after different doses. The numbers of overlapping peaks and related kinetic parameters were identified from T_m–T_stop through computerized glow curve deconvolution methods. The dependence of the TL responses on radiation dose was studied and a linear dose response up to 1000 Gy was observed for the samples. Copyright © 2015 John Wiley & Sons, Ltd.     

Luminescence investigation of CaY2Al4SiO12:Dy3+ phosphor synthesized by sol–gel method

Dy³⁺-doped CaY₂Al₄SiO₁₂ phosphors were prepared using the sol–gel method. X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), and energy dispersive spectroscopy analyses (EDS) were used to analyse the crystal structure, morphology, and elemental composition of the prepared samples. The luminescence behaviour of the sample was investigated using photoluminescence (PL) and thermoluminescence (TL) techniques. The prepared CaY₂Al₄SiO₁₂:xDy³⁺ phosphor showed a characteristic blue and yellow emission at ~480 and 583 nm, respectively, with an excitation wavelength of 350 nm. The most intense PL emission was found for a 4 mol% doping concentration of Dy³⁺ ions. The CIE diagram of the phosphor showed bluish-white colour emission. For TL studies, the prepared phosphors were irradiated with a ⁶⁰Co γ (gamma) source and the TL glow curve of the CaY₂Al₄SiO₁₂:0.04Dy³⁺ phosphor showed three overlapped peaks. For the Gaussian peaks, Chen's peak shape method was applied to determine the kinetic parameters of the samples.     

Low and high temperature asymmetric forms of pig kidney and rabbit muscle phosphofructokinases and reversible, temperature-dependent transitions.

Previous viscometric studies from this laboratory (Johnson, C. S., Vogtmann, L., and Deal, W. C., Jr. (1976) Biochem. Biophys. Res. Commun.73, 391–395) have shown that at 3.5 ° C, pig kidney phosphofructokinase (PFK) is markedly asymmetric and rabbit muscle PFK is moderately asymmetric. The present viscometric and ultracentrifugal studies show that both enzymes are also asymmetric at near-physiological temperatures, that both exist in high-temperature and low-temperature forms, and that the high-temperature forms of both are less asymmetric and more dissociated than the low-temperature forms. The risults also show that the transitions from low- to high-temperature forms are reversible if the exposure to 35 °C is short enough that no irreversible chemical modification occurs. For pig kidney PFK, intrinsic viscosity values of 34.0, 25.6, and 13.8 ml/g were obtained at 3.5, 20 and 35 °C, respectively, whereas rabbit muscle PFK yielded values of 6.9, 6.2, and 5.2 ml/g at the corresponding temperatures. These data clearly show a decrease in asymmetry with increase in temperature. However, both enzymes are still asymmetric at the higher temperature, inasmuch as most globular macromolecules have intrinsic viscosity values in the range of 3 to 4 ml/g, regardless of molekular weight. Studies from 1 to 45 ° C at a fixed protein concentration (4.8 mg/ml) showed that pig kidney PFK has reduced viscosity values of 51.0 ml/g (low-temperature form) and 20.4 ml/g (high-temperature form) in plateau regions of the viscosity graph at the temperature extremes; the mid-point of the transition between the two forms is at about 22–24 °C. Rabbit muscle PFK at 4.2 mg/ml reproducibly gave corresponding reduced viscosity values of 6.9 and 4.8 ml/g for the low- and high-temperature forms, respectively; the transition mid-point between the two forms is at about 16 °C. The first reported sedimentation velocity studies of rabbit muscle PFK at near-physiological temperature (35 °C) show that with near-physiological protein concentration (1.25 mg/ml), the enzyme is in a much more dissociated form, s_20,w(weight average) = 14. 5 S; s_20,w(peak leading edge) = 17 S, than that previously reported at lower temperatures, s_20,w(fastest peak) = 23–30 S. Similarly, the first sedimentation studies on the pig kidney enzyme indicate a lower sedimentation coefficient at 35 ° C (s^0.39%_20,w = 48 S) than at 3.5 ° C(65 S).     

Luminescence characterization of Dy and Eu doped Na6Mg(SO4)4 phosphors

A series of single‐phase phosphors based on Na₆Mg(SO₄)₄ (Z_eff = 11.70) doped with Dy and Eu was prepared by the wet chemical method. The photoluminescence (PL) and thermoluminescence (TL) properties of Dy³⁺‐ and Eu³⁺‐activated Na₆Mg(SO₄)₄ phosphors were investigated. The characteristic emissions of Dy³⁺ and Eu³⁺ were observed in the Na₆Mg(SO₄)₄ host. The TL glow curve of the Na₆Mg(SO₄)₄:Dy phosphor consisted of a prominent peak at 234°C and a very small hump at 158°C. The TL sensitivity of the Na₆Mg(SO₄)₄:Dy phosphor was found to be four times less than the commercialized CaSO₄:Dy phosphor. The TL dose–response of the Na₆Mg(SO₄)₄:Dy phosphor was studied from a dose range of 5–10 kGy and the linear dose–response was observed up to 1 kGy which is good for a microcrystalline phosphor. Trapping parameters for both the samples were calculated using the Initial Rise and Chen's peak shape methods.     

Comparison of thermoluminescence characteristics in γ‐ray and C5+ ion beam‐irradiated LiCaAlF6:Ce phosphor

We compare the thermoluminescence (TL) behavior of Ce³⁺ ion‐activated LiCaAlF₆ exposed to γ‐rays and a carbon ion beam. The reported phosphor is synthesized using an in‐house precipitation method with varying concentrations of activator ion and is characterized by X‐ray diffraction (XRD) and TL. Rietveld refinement is performed to study the structural statistics. The TL glow curve consists of a prominent glow peak at 232°C with three shoulders at 115, 159 and 333°C when exposed to γ‐rays from a ⁶⁰Co source. When exposed to a C⁵⁺ ion beam, the TL glow curve consists of five peaks with peak temperatures near 156, 221, 250, 287 and 330°C, and is found to vary slightly with changing fluence. Glow curve convolution deconvolution (GCCD) functions are applied to the TL curves for complete analysis of the glow curve structure and TL traps. The order of kinetics (b), activation energy (E) and frequency factor are determined using Chen's peak shape method and theoretical curves are drawn using GCCD functions. A track interaction model (TIM) is used to explain the sublinearity/saturation at higher fluences. Ion beam parameters are analyzed using Monte‐Carlo simulation‐based SRIM‐2013 code. Copyright © 2016 John Wiley & Sons, Ltd.     

Synthesis and thermoluminescence characterizations of Sr2B5O9Cl:Dy3+ phosphor for TL dosimetry

The photoluminescence (PL) and thermoluminescence (TL) displayed by Dy‐activated strontium haloborate (Sr₂B₅O₉Cl) were studied. A modified solid‐state reaction was employed for the preparation of the phosphor. Photoluminescence spectra showed blue (484 nm) and yellow (575 nm) emissions due to incorporation of Dy³⁺ into host matrix. The Dy‐doped (0.5 mol%) Sr₂B₅O₉Cl was studied after exposure to γ‐irradiation and revealed a prominent glow curve at 261°C with a small hump around 143°C indicating that two types of traps were generated. The glow peak at the higher temperature side (261°C) was more stable than the lower temperature glow peak. The TL intensity was 1.17 times less than that of the standard CaSO₄:Dy thermoluminescence dosimetry (TLD) phosphor, the phosphor showed a linear dose–response curve for different γ‐ray irradiation doses (0.002–1.25 Gy) and fading of 5–7% was observed for higher temperature peaks upon storage. Trapping parameters and their estimated error values have been calculated by Chen's peak shape method and by the initial rise method. Values of activation energies estimated by both these techniques were comparable. The slight difference in activation energy values calculated by Chen's peak shape method indicated the formation of two kinds of traps Furthermore, slight differences in frequency values are due to various escaping and retrapping probabilities. Copyright © 2014 John Wiley & Sons, Ltd.     

Evaluation of trapping parameters of γ‐rays irradiated Dy3+‐doped LaPO4 phosphors

Thermoluminescence (TL) materials are widely used in radiation measurements. The best‐known applications of TL materials are in the dosimetry of ionizing radiation, and in CTV screen phosphors, scintillators, X‐ray laser materials, etc. The TL glow curve and its kinetic parameters for annealed LaPO₄ at different constant temperatures and for Dy³⁺‐doped LaPO₄ phosphors irradiated by gamma‐rays are reported here. The samples were irradiated using a ⁶⁰Co gamma‐ray source at a dose of 10 Gy and the heating rate used for TL measurements was 5ºC/s. The samples were characterized using X‐ray diffraction (XRD), Fourier transform infrared, transmission electron microscopy and TL techniques. The XRD pattern shows that the prepared phosphor has a good crystalline structure with an average crystallite size of ~ 18 nm. The samples show good TL peaks for 0.05, 0.1 and 0.2 mole % doping concentrations of Dy³⁺ ions and anneal above 400ºC. The TL glow curve characteristics of annealed LaPO₄ and Dy³⁺‐doped LaPO₄ were analyzed and trapping parameters calculated using various methods. All TL glow curves obey the second‐order kinetics with a single glow peak, which reveals that only one set of trapping parameter is set for a particular temperature. The TL sensitivity was found to depend upon the annealing temperature and Dy³⁺ doping concentration. The prepared sample may be a new nano phosphor and be useful in TL dosimetry. Copyright © 2014 John Wiley & Sons, Ltd.     

Luminescence characteristics of Na3Ca2(SO4)3F: Ce3+ fluoride material

A new Na₃Ca₂(SO₄)₃F: Ce³⁺ phosphor synthesized by a solid state diffusion method is reported. The photoluminescence study showed a single high intensity emission peak at 307 nm wavelength when excited by UV light of wavelength 278 nm. An unresolved peak of comparatively less intensity was also observed at 357 nm along with the main peak. The characteristic emission of dopant Ce in Na₃Ca₂(SO₄)₃F phosphor clearly indicated that it resides in the host lattice in trivalent form. The emission peak can be attributed to 5d → 4f transition of rare earth Ce³⁺. The prepared sample is also characterized for its thermoluminescence properties. The TL glow curve of prepared sample showed a single broad peak at 147°C. The trapping parameters are also evaluated by Chen's method. The values of trap depth (E) and frequency factor (s) were found to be 0.64 ± 0.002 eV and 1.43 × 10⁷ s^–1 respectively. The study of PL and TL along with evaluation of trapping parameters has been undertaken and discussed for the first time. Copyright © 2014 John Wiley & Sons, Ltd.     

Synthesis,characterization and thermoluminescence studies of (ZnS)1‐x(MnTe)x nanophosphors

The present paper reports the thermoluminescence (TL) of (ZnS)_1‐x(MnTe)_x nanophosphors that were prepared by a wet chemical synthesis method. The structure investigated by X‐ray diffraction patterns confirms the formation of a sphalerite phase whose space group was found to be F 3m. From XRD, TEM and SEM analyses the average sizes of the particles were found to be 12 nm, 11 nm and 15 nm, respectively. Initially the TL intensity increased with increasing values of x because the number of luminescence centres increased; however, for higher values of x the TL intensity decreased because of the concentration quenching. Thus the TL, mechanoluminescence and photoluminescence intensities are optimum for a particular value of x, that is for x = 0.05. Thermoluminescence of the (ZnS)_1‐x (MnTe)_x nanophosphor has not been reported previously. There were two peaks seen in the thermoluminescence glow curves in which the first peak lay at 105–100 °C and the second peak lay at 183.5–178.5 °C. The activation energies for the first and second peaks were found to be 0.45 eV and 0.75 eV, respectively.     

Electronic structure and defect-induced luminescence study of phase-stabilized t-ZrO2 nanocrystals

Luminescent tetragonal-ZrO₂ (t-ZrO₂) nanocrystals were synthesized using an optimized combustion method without post-synthesis annealing and characterized using X-ray diffraction, electron microscopy, Raman spectroscopy, X-ray photoelectron spectroscopy, UV–Vis. spectroscopy, photoluminescence spectroscopy, thermoluminescence (TL), and vibrating sample magnetometry. The as-synthesized t-ZrO₂ nanocrystals have a bandgap of 4.65 eV and exhibit defect-assisted blue emission (Commission Internationale de I'Elcairage coordinates 0.2294, 0.1984) when excited at 270 nm. The defect states were qualitatively and quantitatively analyzed using TL after irradiating nanocrystals with γ- and UV radiations at various doses. The TL glow curves show intense emission in the high-temperature region from 523 to 673 K for both UV- and γ-irradiated samples; however, another less-intense TL peak was also observed in the low-temperature region from 333 to 453 K with γ irradiation at higher doses, indicating the formation of shallow trapping states. The activation energies, frequency factor, and order of kinetics were estimated using the computerized glow curve deconvolution method for the shallow and deep traps for γ- and UV-irradiated samples. The present study shows that phase-stabilized t-ZrO₂ nanocrystals are potential candidates for luminescence-based applications.     

An analysis of photosynthetic response and adaptation to temperature in higher plants: temperature acclimation in the desert evergreen Nerium oleander L*

Abstract. Factors underlying the process of photosynthetic acclimation to temperature were investigated for the shrub Nerium oleander L. Ramets of a single clone were grown under day/night temperature regimes of 20°C/15°C or 45°C/32°C. Plants grown at the lower temperature regime possessed rates of photosynthesis twice that of the high-temperature grown plants when CO₂ fixation was measured at 20°C. In contrast, the plants grown at the high-temperature regime had twice the rate of CO₂ fixation of the 20°C/l 5°C-grown plants at a measurement temperature of 45° C. It was determined that the ability to acclimate to changes in temperature regime was present in fully mature leaves. A reciprocal transfer of plants between the two growth regimes resulted in the appearance of the CO₂ fixation characteristics appropriate to the new growth temperature after 12–14d. The response of CO₂ fixation to light, temperature, and CO₂ partial pressure and the temperature responses of soluble and membrane-bound photosynthetic enzyme systems were analysed to determine which components might be responsible for the superior photosynthetic performance of the 20°C/I5°C-grown plants at 20°C, and the enhanced high-temperature stability of the 45°C/32°C plants. The measured photosynthetic capacity of the 20°C/15°C plants could not be attributed to gross morphological, stomatal, or other physical changes, or to a general increase in the concentration of components of the photosynthetic process. Only a single enzyme, Fru-P₂ phosphatase, was affected to an extent similar to that of photosynthesis. The enhanced thermal stability of the 45°C/32°C plants may be attributed primarily to an enhanced stability of the chloroplast membrane-bound enzymatic activities and the stability of the photosynthetic carbon metabolism enzymes which require lighl for activation.