The Ba3MgSi2O8:Eu2+, Mn2+ shows three emission colors: 442, 505, and 620 nm. The 442 and 505 nm emission originate from Eu2+ ions, while the 620 nm emission originates from Mn2+ ions. The excitation bands of three emission colors are positioned around 375 nm. Electron paramagnetic resonance measurement demonstrates that Eu2+ ions are occupied with three different Ba2+ sites. The red emission of Mn2+ ions has a long decay time of 750 ms due to persistent energy transfer from oxygen vacancies to Mn2+ ions, while the blue and green bands of Eu2+ ions have decay times of 0.32 and 0.64 μs, respectively. The fabricated white-light emitting diode using a 400-nm-emissive chip with a white-light emitting Ba3MgSi2O8:Eu2+, Mn2+ phosphor shows warm white light and higher color stability against input power in comparison with a commercial GaN-pumped (Y1−xGdx)3(Al1−yGay)5O12:Ce3+ phosphor.

No abstract

No abstract

Optical properties of SrBi2Ta2O9 (SBT) ferroelectric thin films were investigated by spectroscopic ellipsometry at room temperature in the 1.5–5.5 eV spectral range. The films were grown on platinized silicon (Pt/Ti/SiO2/Si) with a Bi/Sr ratio (x) range from 1.2 to 2.8 by pulsed-laser deposition. The measured pseudodielectric functions of the samples indicate the band-gap energy of SBT shifts to lower energies as x increases. The optical constants and band-gap energies of the SBT films were determined through multilayer analyses on their pseudodielectric functions. The band-gap energy of SBT is found to shift to lower energies quite linearly with x. The band-gap energy at stoichiometric composition (x=2) is estimated to be 4.1 eV.

No abstract