Search

The decomposition of synthetic siderite (FeCO3) in air atmosphere at room temperature conditions was studied. Siderite was formed by mechanochemical reaction of Fe3O4 and graphite at high CO2 pressure in the presence of water. Kinetics of decomposition reaction was studied over period up to 9 days and it is shown that decomposition reaction obeys geometrical contraction solid-state reaction mechanism model. It was found that the water influences not only the kinetics of siderite formation but also its stability. Siderite completely decomposes at ambient conditions yielding magnetite (Fe3O4) and hematite (Fe2O3) which can reversibly re-absorb carbon dioxide.

(Hf1-xZrx)B2 solid solution powders were synthesized by two methods. First, solution-based processing of HfCl4, ZrCl4, sucrose, and H3BO3 was conducted followed by heat treatment in Argon to carry out the carbothermal reduction (CTR) reaction to form the diboride powders. Alternatively, in the so-called borohydride reduction (BHR) method, HfCl4, ZrCl4 and NaBH4 were mixed in an Argon glove box followed by heat treatment in Argon at 700−1500 °C. The synthesized powders were characterized by XRD, SEM, TEM, EDS, and TGA, and the influence of different parameters such as starting composition, heat treatment temperature and time on products characteristics were revealed. Both CTR and BHR solid solution powders were then consolidated within ∼5 min in a homemade flash sintering (FS) setup. The composition, microstructure, hardness, and thermal-oxidation properties of flash sintered ceramics were characterized, and the implication of this study and directions for future research were discussed.

Understanding the reaction process governing the formation of sol–gel sulfurized copper zinc tin sulfide (Cu2ZnSnS4, CZTS) films and the growth of other secondary sulfide phases is crucial to process optimization and solar cell device performance. In the current study, sulfurization of the relevant single Cu oxide, single Sn oxide, and Cu-Sn oxide films related to the Cu-Zn-Sn-S system was carried out in 100 ppm H2S + 4%H2 + 96%N2 (by volume) at low to intermediate temperatures. At intermediate temperature of 350°C, sulfurization of Cu oxide, Sn oxide, and Cu-Sn oxide precursors showed no evidence for the formation of any binary or ternary sulfide phase(s) as observed during the in situ Raman monitoring experiments. These observations were also confirmed by subsequent x-ray diffraction (XRD) and energy-dispersive spectroscopy (EDS) analyses, while the stoichiometric Cu-Zn-Sn oxide film underwent a direct reaction between the oxides and H2S to form CZTS without binary or ternary impurities. In comparison, at lower temperature of 170°C, sulfurization of the single Cu oxide, Sn oxide precursors in 100 ppm H2S + 4%H2 + 96%N2 led to the formation of simple sulfides such as Cu2−xS (with x close to 1) and SnS2. As a result, despite sulfurization of sol–gel-based stoichiometric Cu-Zn-Sn oxide film at 170°C in the same gas mixture leading to CZTS formation, extended exposure to 100 ppm H2S leads to over-sulfurization and formation of detrimental impurities, especially CuS. The implications of the results with respect to the understanding and optimization of the phase formation process for CZTS light absorber material are discussed, and the direction for future research is suggested.

Flash sintering is an electrical field-assisted densification technique that requires passing a current through a ceramic powder compact. Pressure-assisted flash sintering of commercially available Zirconium Nitride (ZrN) powders has been demonstrated. Near fully dense samples can be obtained within a short period of time. The influences of parameters such as electrical field strength, voltage ramping rate, current limit, external pressure, pre-heating, and holding time on the onset of the flash event were investigated. Some post-flash sintered samples were subjected to the same condition to observe if the material would experience repeated flash. In addition, material properties such as density and hardness were measured and correlated with SEM and XRD. Implications of the observations on underlying flash sintering mechanism will also be discussed.

Herein we describe a modeling work on gradient refractive index (GRIN) lenses which could be fabricated from utilizing a mixture of a photocurable (Hydroxyethyl) methacrylate and epoxy prepolymer resins. Simulations based on the polymer properties show measurable and tunable optical properties such as spherical aberrations.

The current research focuses on the role of oxygen partial pressure on structure and phase transitions of (1-x)Pb(Mg1/3Nb2/3)O3-xPbTiO3 with x = 0.28 (PMN-28PT). The changes in oxygen content have been traced through weight gain/loss during 160 cycles between 250 and 300 °C. The structural phase transitions have been investigated by in-situ high temperature powder X-ray diffraction and high temperature Raman spectroscopy. The variations in oxygen content in PMN-28PT result in structural changes and have a significant effect on electrical impedance. It is suggested that bonding between oxygen and Ti and Pb atoms in the perovskite structure of PMN-28PT can be controlled by low oxygen partial pressure heat treatment.

Carbon dioxide capture/release reactions using magnetite, Fe3O4, and hematite, Fe2O3, as sorbents were studied. Kinetics of mechanically activated chemical reactions between iron oxides and CO2 was investigated as a function of CO2 pressure and planetary ball mill process parameters. It was found that complete carbonation of iron oxides can be accomplished at room temperature and elevated CO2 pressure (10–30 bar). Siderite calcination was studied in vacuum and argon atmospheres. FeCO3 can be decomposed at 367 °C yielding magnetite, carbon and/or iron. This mixture can reversibly re-absorb carbon dioxide in multiple carbonation–calcination cycles. These results suggest that siderite or iron oxides are prospective and efficient reversible sorbents for CO2 capture. Keywords: Iron oxides, CO2 capture capacity, Carbonation, Mechanically activated chemical reactions, Calcination, Reversible sorbent

We report the catalyst-free synthesis of monolithic mesoporous nanopolycrystalline diamond from periodic mesoporous carbon at pressures between 15 and 21 GPa and a temperature of 1300 °C. We investigated the pressure-dependence of the porosity with 3-dimensional electron tomography. We have observed that surface areas increase from 56 to 90, 138 m2 g−1, and porosities increase from 10, 24, to 33% for materials produced at 15, 18, and 21 GPa, respectively. The increased porosity at higher pressure may be due to the earlier onset of the nucleation of diamond at higher pressure.

PrNi0.5Co0.5O3-δ (PNC) cathode material demonstrates total electrical conductivity on the order of ~300 S/cm at 400-600oC in air, and the conductivity shows a slight increase as temperature increases with an activation energy (from ln(σT) vs 1/T plot) of 10.9 kJ/mol. The introduction of water vapor (H2O) leads to a small (~0.16%) increase in total resistivity, which is reversible upon water removal and explained, tentatively, by the defect reaction of H2O + 2Oo x + 2h• = 2(OH)O • + 0.5O2. The thermal expansion coefficient (TEC) of PNC is measured to be 17.6×10-6/K by dilatometry and 18.43×10-6/K by in situ XRD up to 800oC. On the other hand, despite bulk chemical stability for both PNC and BZCYYb4411 powders against low percentage H2O and CO2, a PNC cathode symmetrical cell over proton conducting BaZr0.4Ce0.4Y0.1Yb0.1O3-δ (BZCYYb4411) electrolyte shows degradation (or increase) in interfacial resistance upon introduction of 3% moisture or 5% CO2 into simulated air at temperature in the range of 650 to 450oC. In comparison, oxygen ion conducting symmetrical cells with PNC cathode and Ce0.9Gd0.1O2-δ (GDC) electrolyte show no change upon H2O and CO2 introduction. The observed sensitivity of the PNC cathode proton conducting symmetrical cell to H2O and CO2 is attributed to the preferred adsorption of H2O and CO2 molecules onto the BZCYYb4411 proton conducting electrolyte surface than on the PNC cathode, and such an explanation is supported by temperature programmed desorption (TPD) measurements for H2O and CO2 on both PNC and BZCYYb4411 powders.

Human Immunodeficiency Virus Type 1 (HIV-1) remains one of the leading causes of death worldwide. Present combination antiretroviral therapy has substantially improved HIV-1 related pathology. However, delivery of therapeutic agents to the HIV reservoir organ like Central nervous system (CNS) remains a major challenge primarily due to the ineffective transmigration of drugs through Blood Brain Barrier (BBB). The recent advent of nanomedicine-based drug delivery has stimulated the development of innovative systems for drug delivery. In this regard, particular focus has been given to nanodiamond due to its natural biocompatibility and non-toxic nature–making it a more efficient drug carrier than other carbon-based materials. Considering its potential and importance, we have characterized unmodified and surface-modified (-COOH and -NH2) nanodiamond for its capacity to load the anti-HIV-1 drug efavirenz and cytotoxicity, in vitro. Overall, our study has established that unmodified nanodiamond conjugated drug formulation has significantly higher drug loading capacity than surface-modified nanodiamond with minimum toxicity. Further, this nanodrug formulation was characterized by its drug dissolution profile, transmigration through the BBB, and its therapeutic efficacy. The present biological characterizations provide a foundation for further study of in-vivo pharmacokinetics and pharmacodynamics of nanodiamond-based anti-HIV drugs.

The graphene oxides (GO) were prepared by a ball milling process with potassium perchlorate as oxidizing agent and deionized water as milling medium. GO samples were synthesized at different processing times and compared with a sample prepared by the Hummer's method. The prepared graphene oxides have been studied by Fourier transform infrared (FTIR), Raman spectroscopies, powder X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). FTIR spectroscopy indicates presence of oxygen-bearing functional groups on the surface, Raman spectroscopy, XRD, SEM and TEM analysis confirm GO formation in ball milling. The sample processed for 12 h (GO 12 h) showed the highest yield of the product, presenting a suitable particle size (40 nm) for biomedical applications, especially in drug delivery systems. Ball milling can be considered as suitable method to obtain GO due to time processing, good quality of product and chemical components used.

In this work, we demonstrate the application of high pressure conditions to enable the direct synthesis of α-AgGaO2 via a solid state reaction of Ag2O and Ga2O3. Synthesis experiments were carried out at pressures and temperatures up to ∼10 GPa and ∼600 °C, respectively, using a resistively-heated diamond anvil cell. Thus synthesized α-AgGaO2 samples were characterized and their chemical composition and crystal structure were confirmed. In particular, electron diffraction confirmed the rhombohedral delafossite crystal structure of the synthesized AgGaO2 and its corresponding lattice parameters of a = 2.99 A and c = 18.43 A. The vibrational modes analysis was also conducted using a combination of ab initio density functional theory (DFT) and Raman spectroscopy. This analysis yielded good agreement between the calculated Raman-active modes and experimental Raman data. Finally, the application of the GGA + U formalism-based on DFT to calculate the electronic band structure of α-AgGaO2 provided a more realistic theoretical band gap value than those reported previously.

Compressibility of the Ti3AlH6 and Ti3AlD6 has been studied by X-ray diffraction method using advanced synchrotron technique up to 38 GPa. Significantly higher values of bulk modulus have been revealed for the hydride and deuteride compounds as compared to the initial pure intermetallic compound. The consequences of this observation have been discussed in terms of ductility and strength of obtained materials. Possible explanation of the peculiarity in the equation of states for both compounds is proposed on the base of the difference in repulsion interactions of hydrogen and deuterium species in the metallic lattice. All advantages of the hydrogenation of titanium aluminum compound have been summarized.

Formation of kesterite CU2ZnSnS4 (CZTS) thin films from sulfurization of sol-gel derived oxide precursor was successfully monitored using advanced in situ Raman microspectroscopy from room temperature up to ∼350°C. The obtained in situ Raman data revealed the emergence of CZTS phase after 30 minutes of sulfurization at 350°C in 100 ppm $\mathbf{H}_{2}\mathbf{S}+4\%\mathbf{R}_{2}+\mathbf{N}_{2}$ gas mixture, while Cu2s phase was observed to form upon continued sulfurization, which was attributed to the slight Cu-rich recipe used. Both phases remained stable upon cooling the sample down to room temperature. Room temperature XRD and EDS data for the in situ examined sample confirmed that CZTS phase successfully formed with its surface decorated by Cu2s particles.

Nano-scratch behavior of ultrahigh molecular weight polyethylene (UHMWPE) reinforced with graphene nanoplatelet (GNP) in varying composition of 0, 0.1, 0.5 and 1 wt% is reported. Hot pressed composite structures are characterized for their tribological behavior in scratch mode using a normal load of 100–300 μN. Increasing GNP content from 0.1 to 1 wt% results in lowering of the coefficient of friction due to easy shear of graphene nanoplatelets. Graphene reinforcement also increases the wear resistance by more than four times, which is a combined effect of lubrication as well as toughening offered by GNPs.

We have studied the phase transformation behavior of the potential hydrogen storage compound ammonia borane at low temperature (from room temperature down to 90 K) and high pressure (from ambient pressure to 9.5 GPa at room temperature and up to 15 GPa at 90 K) region using the diamond anvil cell. This material shows four new phase transitions in this pressure and temperature region. The phase transition phenomenon is evidenced by the splitting of the peak and/or the appearance of the new peak in the Raman spectra as well as by the change of the pressure coefficient of the Raman modes. The phase boundaries between these phases are also established from the data collected during different cooling cycles. These results provide the information about the stability of the bonding characteristics of this potential hydrogen storage material at low temperature and high pressure region.

In this paper, we report the effect of subsequent electrochemical anodization and cathodization subjected to single walled carbon nanotubes. The performance of the single walled carbon nanotubes before and after activation was evaluated electrochemically using different charged redox probes and a biologically important neurotransmitter-dopamine. Further, for the first time, the surface of single walled carbon nanotubes before and after electrochemical activation was also evaluated using Raman Spectroscopy. Electrochemical results indicated that the pretreatment method employed in this work greatly enhanced the performance of single walled carbon nanotubes towards the detection of the model analytes employed. The observed enhancement in the signal is attributed to the rupture of the basal plane found on the end caps of carbon nanotubes giving rise to a larger density of edge-plane like defects on the single walled carbon nanotubes surface. A detection limit of 10 nM (based on three times the standard deviation of the slope) was also estimated when dopamine was monitored using electrochemically activated single walled carbon nanotube electrodes. In addition, the electrochemically activated carbon nanotubes exhibited a improved selective and sensitive detection of our model analyte dopamine with a minimal electrode fouling of about 3% +/- 1.2% (N = 4).

Mg2FeH6 was synthesized by ball milling MgH2 and Fe (2:1 molar ratio) mixture for 72 h followed by heating at 400 °C under H2 pressure. The hydride formation, its structure and homogeneity were investigated by scanning electron microscopy, X-ray diffraction, transmission electron microscopy and Raman spectroscopy. High pressure in situ synchrotron X-ray diffraction and Vienna ab initio simulation were used to determine bulk modulus of the sample. The bulk modulus of Mg2FeH6 was found to be 75.4(4) GPa by optimized experiment and 76.3 GPa by theoretical simulation. From high temperature in situ X-ray diffraction study the volumetric thermal expansion coefficient of Mg2FeH6 was found to be αv = 5.85(3) × 10−5 + 7.47(7) × 10−8 (T − To)/°C. Decomposition of Mg2FeH6 was observed at 425 °C and the decomposition products were Mg, Fe and H2.

High pressure Raman scattering on Mo(CO)6 up to 37.7 GPa at ambient temperatures are recorded inside the Diamond-Anvil-Cell (DAC). The Raman spectra of the molybdenum hexacarbonyl completely vanish at 23.3 GPa, signifying novel pressure induced decomposition. The decomposed Raman spectrum recovered at ambient conditions has the characteristic features of a highly dense polymer with δ(OCO) units possibly attached to metal centers, C=O functional group, and graphitic carbon; and also CO adsorbed to molybdenum metal centres. The so formed highly dense metal mediated polymer upon relaxation from high pressure conditions and upon exposure to 514.5 nm argon ion laser outside the DAC transforms to MoO3 in the presence of disordered carbon as characterized by the Raman modes.

Phase stability of titanium hydride (TiH2) was studied at high pressure-high temperature conditions using synchrotron radiation under non-hydrostatic conditions. Resistive heating method was used to heat the sample to a maximum temperature of 873 K in a diamond anvil cell (DAC) under pressure up to 12 GPa. Pressure–temperature behavior was studied by varying the temperature upto 823 K in steps of 50 K with pressure variations within 3 GPa. Structural phase transformation from tetragonal (I4/mmm) to cubic (Fm-3 m) was observed with increase in temperature. Tetragonal phase was found to be stabilized when the sample was subjected to pressure and temperature cycle.

A zero-emission process of hydrogen production from fossil fuel through a system of reactions involving hydroxide, carbon, CO, CO2 and water is described here. It provides for a complete sequestration of carbon (CO2 and CO) from coal/natural-gas burning plants. The CO and or CO2 produced in coal or natural gas burning power plants and the heat may be used for producing hydrogen. Economically hydrogen production cost is less than the current price of fossil-fuel produced hydrogen with the added benefit of carbon sequestration. The reduced cost of the hydrogen may aid in making a hydrogen fueled automobile economically viable.

High-pressure Raman spectra (300–2200 cm −1 ) of crystalline Cr(CO) 6 at room temperature for pressures up to 29.5 GPa have been recorded. A probable second-order phase transition is assigned at ∼4.1 GPa. Recorded Raman spectra started to vanish at 20.8 GPa and upon further increase in pressures resulted in complete vanishing at 29.5 GPa. The dν/d p values suggest the breakdown of Dewar–Chatt–Duncanson model for the first time in homoleptic mono carbonyls which has been discussed. Decomposition of Cr(CO) 6 leads to the formation of polymeric CO with characteristic sp 2 carbon and (OCO) units for the first time.

Hydrogen generating reaction between sodium borohydride, NaBH4, and magnesium hydroxide, Mg(OH)2 (brucite), was studied. Reaction rate was found to depend on the degree of reactants homogenization and/or their particle size. Kinetic of the reaction was studied in isothermal approach in the temperature range of 240–360 °C. It is shown that the reaction obeys 2D diffusion mechanism and its activation energy is 155.9 kJ/mol. Powder XRD analysis and Raman spectroscopy reveal that mechanically activated mixture of NaBH4 and Mg(OH)2 reacts yielding MgO as the only crystalline phase in the temperature range of 240–318 °C. At higher temperatures a new crystalline tetragonal phase of as yet undetermined composition is developed.

α-AgGaO2 is prepared via hot pressing of Ag2O and Ga2O3 (diamond anvil cell, 10 GPa, 600 °C, 2 h).

Detailed investigations of the photoluminescence properties of Mn4+ (3d3) ions in YAlO3 have been performed in the temperature range 10–600 K. The luminescence of Mn4+ ions due to the transition consists of two zero-phonon lines (R lines) at 691.3 and 692.7 nm, which became visible only at low temperature, and their vibronic sidebands that cover the range of 660–740 nm. The thermal quenching of the luminescence intensity due to the non-radiative decay occurs at temperatures above 420 K. The temperature dependence of the luminescence decay time shows a quasi-linear decrease from τ = 4.9 to 1.6 ms in the temperature range from 90 to 420 K (with a temperature coefficient −0.01 ms K−1) that makes YAlO3:Mn a potentially good phosphor for a fibre optic fluorescence thermometer in this temperature range. The high-pressure low-temperature luminescence measurements in a diamond-anvil cell reveal similar pressure coefficients for Mn4+ and Cr3+ dopant ions in YAlO3, equal to 1.16 cm−1 kbar−1 and 1.08 cm−1 kbar−1, respectively.

The paper presents results on study of thermoluminescent dosimetry (TLD) properties of YAlO 3 :Mn crystals for dosimetry of γ-radiation. The TL emission at 530 nm from Mn 2+ ions has been used as a TL signal for detecting of γ-radiation. The studied YAlO 3 :Mn samples have shown a sensitivity to γ-radiation commensurable with commercial LiF:Mg, Ti. Since the YAlO 3 :Mn crystals exhibit linear dose response up to 1 kGy, it makes them a candidate for high-dose dosimetry of ionizing radiation.

The thermoluminescence (TL) of calcium aluminate persistent luminescence materials doped with Eu 2+ and co-doped with R 3+ ions were studied between 20 and 325 K. The basic material, CaAl 2 O 4 :Eu 2+ , showed three TL bands between 150 and 300 K in the glow curve. Changing the R 3+ co-dopant to the adjacent element in the rare earth series affects significantly the thermoluminescence intensity and even the position of the glow curve maximum. The physical effect seemed to be removing the traps since the La 3+ , Y 3+ , and Lu 3+ ions suppressed the thermoluminescence. The Pr 3+ , Ho 3+ , and Dy 3+ co-doping enhanced mainly the low temperature traps and these materials have an intense but relatively short persistent luminescence at room temperature. The Nd 3+ and Tm 3+ ions enhanced the TL bands close to room temperature and are thus the most suitable co-dopants to induce intense and long persistent luminescence. The quenching of the thermoluminescence by Sm 3+ was concluded to be due to the presence of Sm 2+ that removes totally the traps.

We have studied effects induced by γ-radiation and temperature in Mn-doped YAlO3 crystals. The studies have been performed by means of optical spectroscopy that include measuring of optical absorption changes induced by γ-radiation and elevated temperature as well as thermally stimulated luminescence (TSL). It has been shown that under γ-irradiation of YAlO3:Mn crystals, along with the ionization of MnAl4+ ions (MnAl4+→MnAl5++e−), some additional coloration processes take place. This additional coloration is characterized by a wide intense band centered at 26,000– 25,000 cm −1 that is ascribed to color centers intrinsic to YAlO3 lattice. This coloration is removed by the way of crystal warming at T⩾350 K , while the coloration caused by MnAl5+ ions is removed at higher temperature (T⩾500 K ) . The observed TSL glow of irradiated crystals reveals three peaks near 360, 400 and 500 K that correspond to three types of traps. Parameters of the traps have been determined. The TSL emission corresponds to intra-center luminescence of MnAl4+ and MnY2+ ions. The possible ionization and trapping mechanisms in YAlO3:Mn crystals are discussed.

The paper presents results of thermally stimulated luminescence (TSL) studies of YAlO 3 crystals both pure and doped with rare-earth (Ho 3 + , Tm 3 + , Er 3 + ) and Mn ions performed in the 20-600 K temperature range. The activation energy and frequency factor of traps have been determined. Nature of the traps and role of dopant ions are discussed.

It is shown that the process of thermal relaxation of the photochromic effect in LaGaO 3 crystals proceeds due to transfer of the charges between defects involved in the effect and shallow traps. The crystals exhibit luminescence of Cr 3+ ions, which are an unintentional dopant. However, the emission observed in the thermally stimulated luminescence of the crystals with residual concentration of chromium is associated with luminescent centers different from typical isolated Cr 3+ ions. The spectral properties of these centers are studied.

Color centers created during growth processes as well as formed under various external influences (UV and γ-irradiation, thermal treatments) are studied in YAP–Nd crystals obtained under different technological conditions. The role of impurity ions (including Fe and Cr) in growth and induced crystal coloration as well as models of color centers are discussed.

The results of the absorption and photocurrent measurements and light-induced grating spectroscopy of undoped LaGaO3 crystals near room temperature are presented. Several absorption bands in the visible and near-ultraviolet region have been detected. Reversible photochromic effect has been observed in the nonoxidized crystals. The results of measurements show that the main absorption band in crystals annealed in air, peaked at 22 500 cm, which also coincides with the main band in the photocurrent spectrum, is associated with the hole-related defect. The diffusion of holes is revealed in the light-induced grating’s experiments. The diffusion is thermally activated with an activation energy equal to 0.7560.03 eV. This value of the activation energy of hole diffusion is responsible for large changes of the diffusion coefficients, which increase more than two orders of magnitude between 20° and 70 °C. @S0163-1829~99!00448-8#

The photoconductivity and the temperature dependence of conductivity of YAlO3 and YAlO3: Nd crystals are studied. It is shown that the photoconductivity in YAlO3 is associated with the transfer of charges between trapping levels of defect centers and the conductivity band of examined crystals. An annealing in reducing atmosphere changes the photoelectric properties of YAlO3 crystals.

The nature of stable and transient color centers in Y3Al5O12, Gd3Ga5O12, YAIO3 and LiNbO3 crystals is studied. The color centers are created by various types of irradiatioin. The effect of irradiation on crystal optical properties in visible and ultravioleft range is presented.

We present results of investigation of transient and stable color centers generated in YAlO 3 and YAlO 3 : Nd crystals under the influence of γ, continuous wave and pulsed UV irradiation in the 30–300 K temperature range. Influence of the color centers on lasing characteristics of YAP–Nd crystals is also studied. The models of color centers in the examined crystals are discussed.

A number of hydrides are considered good candidates for hydrogen storage material for various applications in particular for automobile use. A metal hydride is synthesized through the reaction of a metal with hydrogen which is formed on industrial scale either by the electrolysis of water, by heating coke with steam in the water gas shift reaction or using hydrocarbons with steam. This study demonstrates that under certain conditions, it is possible to synthesize a metal hydride by the reaction of a metal with water or with a hydroxide. Such a synthesis route dispenses with the need for separately forming hydrogen by an expensive process and then to synthesize a hydride by metal–hydrogen reaction. If adopted in many of the hydrogen storage projects which plan to use a hydride for producing hydrogen through a chemical reaction or by a reversible dissociation for automobile use, this method could make a significant difference in making them cost-effective.

The color centers, which are generated in yttrium–aluminium perovskite YAP:Nd(1 at.%) and YAP:Er(50 at.%) crystals under the influence of ultraviolet and γ-irradiation, have been studied by absorption spectroscopy. Both stable and transient at room temperature color centers are generated. It is shown that the transient color centers are mainly responsible for the decrease of laser generation efficiency of Nd:YAP and YAP:Er irradiated crystals, although physical mechanisms leading to efficiency decrease are different in these materials.

Radiation induced recharging of Ce 3+ and Ce 4+ ions in Ce and Nd doped yttrium-aluminium garnet crystals was observed. This effect depends on the Ce 3+ ion concentration and the type of ionizing radiation. The crystals investigated were irradiated with gamma-rays, protons with fluences up to 10 14 protons/cm 2 and electrons with a fluence of 5 × 10 16 electrons/cm 2 . Changes in cerium concentration after gamma-irradiation were calculated from the formula of Smakula.

The influence of gamma irradiation on optical and lasing properties of YAG:Er, YAG:CTH, YAG:Nd and YAG:Cr 4+ single crystals were studied. For no thermal annealed rods from YAG:Er and YAG:CTH crystals the increase of laser output energy was established. The mechanisms of radiation sensibilization are discussed.