CaAlSiN3:Eu2+ red phosphors synthesized by atmospheric nitrogen and their luminescence properties

In this paper, we propose one-step and two-step process under atmospheric pressure condition for synthesizing the CaAlSiN3:Eu2+ red phosphors by using nano-sized EuB6 and Eu2O3 as raw doping and activator materials. Moreover, the crystal structures, morphologies and luminescence properties of different-doped-Eu-concentration (2%-10%) samples are characterized in detail. According to energy dispersive spectrometer and X-ray diffraction (XRD) results, the cell volume and B content will gradually increase with the increase of the Eu concentration (2%-10%) for the sample prepared by two-step process. In contrast, the cell volume decreases with increasing the Eu concentration for the one-step prepared sample. Meanwhile, B content in the sample is less than that in the sample mentioned above and O content becomes larger. In addition, under the 460-nm blue light excitation, the two-step synthesized samples (nano EuB6 doped) has the highest emission peak in the 652-680 nm range, however, the sample by one-step synthesis (nano Eu2O3 doped) has strong emission peak only in the 630-637 nm range. Moreover, the intensity of fluorescence of the former one is stronger than that of the latter one. Both XRD and fluorescence spectra show that boron element can be introduced into the matrix by using two-step methods under atmospheric nitrogen. The introduction of boron not only reduces the oxygen content in the matrix but also changes the crystal field around Eu ions to adjust CaAlSiN3:Eu2+ phosphor luminescence peak position. Combining XRD and fluorescence spectral analysis, it is believed that boron element is introduced into the host by the two preparation methods of atmospheric nitrogen. The introduction of boron not only reduces the oxygen content in the matrix but also changes the crystal field environment of Eu2+ ions, and thus adjusting the luminescence peak position of Ca0.94AlSiN3:Eu2+ phosphor. Blue LED excitation of combined green-emitting phosphor and Ca0.94AlSiN3:0.06Eu2+ phosphor doped with nano EuB6 can yield white LED device with a color rendering index of 91 at a corresponding color temperature of 3364 K. This work has adopted a simple method to avoid expensive and complex pressure sintering equipment, and also reduces gas sintering equipment. Therefore, it is has a good prospective in industrial application and reducing the production cost.