(Eu 2+ , Dy 3+ )-co-doped strontium aluminate (SrAl 2 O 4 :Eu 2+ , Dy 3+ ) powder as a mechanoluminescent (ML) phosphor was synthesized via soft mechanochemical pretreatment of precursor mixtures in a stirred media mill and subsequent calcination . Effect of soft mechanochemical pretreatment of precursors on the synthesis process as well as the photoluminescent (PL) and ML properties of SrAl 2 O 4 :Eu 2+ , Dy 3+ phosphor was investigated. The precursor mixtures unground and ground at different time and the resultant phosphors were characterized by laser particle size analysis , X-ray diffraction, scanning electron microscopy, differential scanning calorimetry , Fourier transform infrared spectroscopy and optical property measurement. The results reveal that soft mechanochemical pretreatment of precursor mixture promotes the crystal growth, and reduces the subsequent calcination temperature. SrAl 2 O 4 :Eu 2+ , Dy 3+ phosphor can be obtained via calcining at 1200 °C for precursor mixture ground at 60 min, but formed via calcining at 1400 °C for unground precursor mixture. The phosphor synthesized with precursor mixture ground at 60 min has the maximum PL and ML intensities due to the enhancement of Eu 2+ and Dy 3+ ions into the crystal lattice to form more electron traps . The measurements by a designed ML instrument indicate that the ML intensity increases with increasing impact stress, and decreases with multiple applications of the same impact stress on phosphor disks.
(Eu 2+ , Dy 3+ )-co-doped strontium/calcium aluminate phosphor as one of color-tunable emission materials was synthesized via solid-state reactions at 1300 °C for 3 h. Effect of strontium/calcium ratio on the crystal structure, particle size/morphology as well as photo- and mechano-luminescent properties of the phosphors was investigated by X-ray diffraction, Rietveld method, scanning electron microscopy with energy dispersive X-ray spectroscopy, and spectrophotometry . The mechano-luminescent properties were measured by two mechanical stress instruments (i.e., impact and compression), respectively. The results reveal that a mixed phase with SrAl 2 O 4 and CaAl 2 O 4 has a monoclinic structure with a space group P2 1 for Sr x Ca 1-x Al 2 O 4 : 0.001Eu 2+ , 0.001Dy 3+ phosphor (x = 0.2–0.8), resulting in the change of crystallographic parameters due to different calcium/strontium ratios. According to the results of photo- and mechano-luminescent characterizations, SrAl 2 O 4 : 0.001Eu 2+ , 0.001Dy 3+ phosphor (x = 1.0) has a superior mechano-luminescent property rather than CaAl 2 O 4 : 0.001Eu 2+ , 0.001Dy 3+ phosphor (x = 0), although they both have photo-luminescent properties. Furthermore, the CEI diagram indicates that the emission color of the phosphor can be tuned from blue to bluish white and eventually to green, and the mechano-luminescent peak appears and becomes intense as Sr 2+ ions substitute for Ca 2+ ions in the phosphor gradually. In addition, the photo- and mechano-luminescent mechanisms of phosphor were also discussed.
Hao Song,Xiuping Wu,Yanjie Zhang,Shichang Xu,Bing Li
Deep-trap luminescent materials have attracted great attention for optical information storage applications. However, the flexible luminescence films based on red luminescence materials with temperature and infrared response are scarce. In this study, we have successfully developed various novel flexible red emitting films based on Eu 2+ /Dy 3+ co-doped Sr 2 Si 5 N 8 phosphors through screen-printing and spin-coating technologies, respectively. Interestingly, the fabricated flexible luminescence films exhibit unique temperature and infrared responsive properties for optical information storage by releasing photons in response to thermal or infrared stimulation. Notably, deep-trap red emitting Eu 2+ /Dy 3+ co-doped Sr 2 Si 5 N 8 phosphors are crucial for the optical information storage properties of the films. Two emission peaks of Sr 2 Si 5 N 8 :Dy 3+ phosphors at 476 nm and 577 nm are observed under excitation at 345 nm, corresponding to the radiative transition occurs from the 4 F 9/2 level to the 6 H 13/2 and 6 H 15/2 levels of Dy 3+ . When Dy 3+ and Eu 2+ ions are co-doped in Sr 2 Si 5 N 8 , the energy transfer from Dy 3+ to Eu 2+ in Sr 2 Si 5 N 8 matrix is found and the decay time confirms that Dy 3+ ions can be acted as deep trap centers to storage photons. For Sr 2 Si 5 N 8 :Eu 2+ ,Dy 3+ phosphors and the corresponding flexible luminescence films, the specific patterns (for example apple and note patterns) are firstly recorded under NUV or blue light excitation and then reappear through thermal stimulation or near-infrared photo-stimulation (980 nm laser). This work not only validates the feasibility of Sr 2 Si 5 N 8 :Eu 2+ ,Dy 3+ phosphors as deep-trap red emitting luminescence materials, but also suggests the applications of flexible luminescence films for optical information storage.
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