A series of Eu 2+ -and Mn 2+ -coactivated CaAl 2 Si 2 O 8 phosphors have been synthesized at 1400 °C under a reduced atmosphere and their luminescence properties have been investigated as a function of activator and coactivator concentrations. We have discovered that energy transfers from Eu 2+ to Mn 2+ by directly observing significant overlap of the excitation spectrum of Mn 2+ and the emission spectrum of Eu 2+ as well as the systematic relative decline and growth of emission bands of Eu 2+ and Mn 2+ , respectively. The critical distance and average separation of Eu 2+ and Mn 2+ have also been calculated. By utilizing the principle of energy transfer, we have also demonstrated that with appropriate tuning of activator content CaAl 2 Si 2 O 8 :Eu 2+ ,Mn 2+ phosphors exhibit great potential to act as a phosphor for white-light ultraviolet light-emitting diodes (UVLEDs).

H atom produced in the thermal decomposition of CH(3)OH highly diluted in Ar (0.48-10 ppm) was monitored behind reflected shock waves by atomic resonance absorption spectrometry (ARAS) at fixed temperatures (and pressures), that is, 1660 (1.73 atm), 1760 (2.34 atm), 1860 (2.04 atm), 1950 (2.18 atm), and 2050 K (1.76 atm) (+/-10 K, respectively). High sensitivity for the H atom has been attained by signal averaging of the ARAS signals down to the concentrations of approximately 1 x 10(11) atoms/cm(3) and enables us to determine the branching fraction for the direct H atom production channel, CH(3)OH --> CH(2)OH + H (channel 1c ) in a mixture of 1 ppm CH(3)OH. Channel 1c is confirmed to be minor, that is, branching fraction for channel 1c is expressed by Log(k(1c)/k(1)) = (- 2.88 +/- 1.88) x 10(3)/T - (0.23 +/- 1.02), which corresponds to k(1c)/k(1) < 0.03 for the present temperature range. By using 0.48 and 1.0 ppm CH(3)OH with (100-1000) ppm H(2), the total decomposition rate k(1) for CH(3)OH --> products is measured from the time dependence of H atom, where the radical products of main channels 1a and 1b , that is, OH, CH(3), and CH(2), were converted rapidly into H atoms. The experimental result is summarized as Log(k(1)/cm(3)molecule(-1)s(-1)) = (-12.82 +/- 0.71) x 10(3)/T - (8.5 +/- 0.38). A theoretical study based on ab initio/TST calculations with high accuracy has been conducted for the reaction: (3)CH(2) + H(2) --> CH(3) + H (reaction 3 ). The rate is given by k(3)/cm(3)molecule(-1) s(-1) = (7.32 x 10(-19))T(2.3) exp (-3699/T). This result is used for numerical simulations to evaluate k(1). Present experimental results on the thermal decomposition rate of CH(3)OH are found to be consistent with previous works. It is also found that time dependence of [H] observed in the 10 ppm CH(3)OH in Ar can be reproduced very well by kinetic simulations by using a reaction mechanism composed of 36 elementary reactions.

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at low pressure (~1 Torr) between 221 and 415 K and a negative temperature dependence was observed: kx = (2.9 ± 0.5) X 10"11 exp((240 ± 50)/7") cm3 molecule"1 s"1. The room temperature value for kx from this study is higher than three previous values. Secondary chemistry associated with high H2S concentrations in the earlier studies is believed to contribute to the discrepancies. DS was used to investigate the isotope effect for reaction 1 and no evidence has been observed for a primary.isotope effect, A:(DS + N02) = (7.3 ± 1.1) X 10'11 cm3 molecule"1 s"1, at 299 K. No reaction was observed with 02 and an upper limit of 1.5 X 10"17 cm3 molecule"1 s"1 was assigned to reaction 2.were measured under pseudo-first-order conditions in a discharge flow system coupled to the spectrometer. The results are A:(HSO + N02) = (9.6 ± 2.4) X 10"12 cm3 molecule'1 s"1; fc(HSO + NO) < 1 X 10"15 cm3 molecule"1 s"1; and k(HSO + 02) < 2 X 10"17 cm3 molecule'1 s'1. All measurements were made at low pressures (1-5 Torr) and room temperature (296 ± 3 K). Experiments were also conducted to determine the products of the HSO + NOz reaction. The results show that a species is produced which reacts with 02 to form H02 with a rate coefficient of (3 ± 2) X 10'13 cm3 molecule'1 s'1 which was determined from the rate of H02 formation. We propose that the unidentified intermediate is HS02.

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