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A series of Eu²⁺- and Mn²⁺-coactivated CaAl2Si2O8 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 Eu²⁺ to Mn²⁺ by directly observing significant overlap of the excitation spectrum of Mn²⁺ and the emission spectrum of Eu²⁺ as well as the systematic relative decline and growth of emission bands of Eu²⁺ and Mn²⁺, respectively. The critical distance and average separation of Eu²⁺ and Mn²⁺ have also been calculated. By utilizing the principle of energy transfer, we have also demonstrated that with appropriate tuning of activator content CaAl2Si2O8:Eu²⁺,Mn²⁺ phosphors exhibit great potential to act as a phosphor for white-light ultraviolet light-emitting diodes (UVLEDs).

Rate coefficients of the reaction O(³P) + HCl in the temperature range 1093−3197 K were determined using a diaphragmless shock tube. O atoms in the ground electronic ³P states were generated either by photolysis of SO2 with a KrF excimer laser at 248 nm or by pyrolysis of N2O with the shock wave. Their concentrations were monitored via atomic resonance absorption excited by emission from a microwave-discharged mixture of O2 and He. Rate coefficients determined in this work show non-Arrhenius behavior, with values consistent with previously reported measurements for T < 1486 K; they fit well with the equation k1(T) = (9.27 ± 0.03) × 10^-24 T ^3.67±0.18 exp[−(1030 ± 160)/T] cm³ molecule^-1 s^-1; listed errors represent one standard deviation in fitting. Theoretical calculations at the CCSD(T)/6-311+G(d, p) level locate a bent ³A‘ ‘ (TS1) and a linear ³A‘ (TS3) transition state characterized previously. On the basis of the results computed by CCSD(T)/ 6-311+G(3df,2p)//CCSD(T)/6-311+G(d,p), the rate coefficients predicted with conventional transition-state theory, including Eckart-tunneling corrections and with variational transition-state theory including zero- and small-curvature tunneling corrections, all agree satisfactorily with experimental observations.

Rate coefficients of reactions (1) CH3S + NO2 and (2) C2H5S + NO2 were determined using laser photolysis and laser-induced fluorescence. CH3S and C2H5S radicals were generated on photolysis of CH3SSCH3 and C2H5SSC2H5, respectively, with a KrF excimer laser at 248 nm. Their concentrations were monitored via fluorescence excited by emission from a dye laser at 371.4 nm (for CH3S) or 410.3 nm (for C2H5S) pumped with a pulsed XeCl excimer laser at 308 nm. Our measurements show that k1 (297 K) = (1.01 ± 0.15) × 10^-10 cm³ molecule^-1 s^-1 is similar to a value reported by Balla et al. and approximately 50% greater than other previously reported values; listed errors represent 95% confidence limits. Reaction 1 has a negative activation energy:  k1 = (4.3 ± 1.3) × 10^-11 exp[(240 ± 100)/T] cm³ molecule^-1 s^-1 for T = 222−420 K. Reaction 2 has a rate coefficient similar to reaction 1 at room temperature:  k2 (296 K) = (1.05 ± 0.16) × 10^-10 cm³ molecule^-1 s^-1 but has a small positive activation energy with k2 = (2.4 ± 0.7) × 10^-10 exp[−(210 ± 80)/T] cm³ molecule^-1 s^-1 for T = 223−402 K. The temperature dependence of k2 is determined for the first time. Reactions of NO2 with HS, CH3S, and C2H5S are compared.