Study On Preparation Of Nano-Sized Long Afterglow Aluminates Phosphors

The nano-sized long afterglow phosphors of SrAl₂O₄:Eu²⁺,Dy³⁺and Sr₄Al₁₄O₂₅:Eu²⁺,Dy³⁺were prepared by a novel method which could be defined as co-precipitation conbined with hydrothermal process.The precursors were obtained by followed steps which related to adding (NH₄)₂CO₃ aqueous solution as a precipitator into a mixed solution contained the ions of Sr,Al,Eu,Dy with stirring under 50～80℃,then hydrothermal treating,washing and drying.The phosphors of Sr₄Al₁₄O₂₅:Eu²⁺,Dy³⁺and SrAl₂O₄:Eu²⁺,Dy³⁺were gained through calcining the precursors at the temperatures of 1000℃～1300℃and under reducing ambience with being presence and no H₃BO₃.The influences of preparation method,the content of the raw materials,reaction temperature and calcining temperature, hydrothermal time and temperature,the ways of feeding and the values of pH on the morphology and luminescent properties of the powders were studied systematically.The properties of the powders were characterized by means of various analytic apparatuses.The shapes of the particles were strip,sphericity and slice and the particle sizes ranged from 50 to 300nm.The most value of the powders brightness reached to 300mcd/m² after being irradiated under UV light(175w,365nm) for 10min and then kept in the dark for 10min.Moreover,both the morphology and brightness of the phosphors could be controlled by changing experimental conditions.The average size of the particles after hydrothermal treatment was smaller than that made by co-precipitation and the powders had more narrow size distribution and better luminescence performances (brightness and afterglow).Compared with the phosphors synthesized by high temperature solid-phase reaction the powders prepared by this process had advantages of more excellent luminescent properties.The brightness of the powers increased firstly and then decreasd with the increase of the reactive and hydrothermal temperatures,and the optimized temperatures were located at 60℃and 200℃respectively.Much more outstanding luminescent properties could be achieved by adjusting pH and calcining temperature.The morphology and luminescent properties of the powders were influenced greatly by the ways of feeding.The brightest phosphors could be obtained by pouring simultaneously the precipitator and nitrates quickly into the reactor. The characteristics of the afterglow would be faded by decreasing the molar ratio of Sr/Al from 0.3 to 0.2.The addition of H₃BO₃ played a very essential role on decreasing crystallization temperature and also enhanced the properties of luminescence.