Abstract
Europium-doped bismuth silicate (Bi4Si3O12) phosphor has been prepared by microwave irradiation method and its crystal structure is determined using Rietveld method. As-prepared phosphor consists of spherical, monodispersed particles with few agglomeration, high crystallinity, and narrow grain size distribution. The phosphor can be efficiently excited in the wavelength range of 260–400 nm, which matched well with the emission wavelengths of NUV LED chips. The photoluminescence spectra exhibit the highest emission peak at 703 nm originating from 5D0 → 7F4 transition of Eu3+ under NUV excitation. The luminescence lifetime for Bi4Si3O12: 2 at% Eu3+ phosphor decreases from 2.11 to 1.86 ms with increasing temperature from 10 to 498 K. This behavior of decays is discussed in terms of radiative and nonradiative decays dependence on temperature. The thermal quenching mechanism of 5D0 emission of Eu3+ in Bi4Si3O12 phosphor is a crossover process from the 5D0 level of Eu3+ to a ligand-to-europium (O2− → Eu3+) charge transfer state. The quantum efficiency of the phosphor under 393 nm excitation is found to be 14.5%, which is higher than that of the commercial red phosphors Y2O3: Eu3+, Y2O2S: Eu3+. The temperature effect on CIE coordinate was discussed in order to further investigate the potential applications.
Highlights
Europium-doped bismuth silicate (Bi4Si3O12) phosphor has been prepared by microwave irradiation method and its crystal structure is determined using Rietveld method
In the search of red emitting phosphors that can be pumped by near-UV or blue emitting LEDs, the nitride based red phosphors and Mn4+ -doped activated oxide/fluoride red phosphors emerged as attractive red phosphor for white LED8–13
For the samples prepared by the microwave synthesis method, the Bi12SiO20 and Bi2SiO5 phases are observed as impurity phases when the calcination temperatures are 650, 700, 800 °C
Summary
Europium-doped bismuth silicate (Bi4Si3O12) phosphor has been prepared by microwave irradiation method and its crystal structure is determined using Rietveld method. The WLEDs based on NUV LED chip coated with tricolor phosphor is not widely used owing to the lack of red phosphors with high conversion efficiency. Mn4+ doped oxide phosphors with broad band emissions exhibit weak absorption for blue excitation light, and Mn4+ doped fluoride phosphors are suffering from thermal stability and high humidity degradation[18]. Eu3+ doped phosphors are probably the better choice because Eu3+-doped phosphors exhibit higher luminescence efficiency and stronger red emission compared with other luminous materials, due to the facts that Eu3+ (4f6) ion emits a narrow band, almost monochromatic light and has a long lifetime of the optically active states[20,21,22,23,24,25,26,27]
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