Preparation of Non-Grinding Long Afterlow Sral2o4:eu2+,dy3+ Materials

Review of preparation of Non-Grinding Long Afterlow SrAl2O4:Eu2+,Dy3+ material by Microwave Combustion Method

Abstract: The long afterglow luminescence materials commonly known as "Noctilucent powder", is a member of photoluminescence materials. Referring to the sun and long-wave ultraviolet irradiation of light source for short periods of time, shutting down after the light source, can still for a long time continuous light-emitting materials. The non-grinding long afterglow SrAl2O4:Eu2+,Dy3+ was prepared by combustion method in home microwave oven directly, after dispersant ,frother, comburent ,and mineralizer were added into the reacting system. Advantages of the microwave combustion are less time, low temperature and no grinding process, and the material made by the method has good luminescent property.

Firstly, Sr(NO3)2(A.R)，Al(NO3)3.9H2O(A.R)，urea(A.R),EDTA(A.R.)，HNO3(A.R.)，H3BO3(A.R.)，PEG200(A.R.)，Eu2O3(99.99%)，Dy2O3(99.99%) were used as raw materials by authors. In the process of preparation of materials, the author obtained the nearly white long persistence materials by the method of microwave. Stoichiometric Eu2O3 and Dy2O3 were dissolved in HNO3 with small quantity of deionized water to obtain Eu3+ and Dy3+ mixed solution. Then Eu3+ and Dy3+ were added in Sr2+ and Al3+ solution with high speed stirring .After the solution was stirred homogeneously, dispresent(PEG200), frother(EDTA), comburent(urea) and mineralizer(H3B03) were added successively, and the whole system was kept at 70℃.

After the completion of sample, SHIMADZU model XRD-6000 X-ray powder diffractometer was used to record the X-ray diffraction patterns of the samples. All excitation, emission spectra and afterglow decay curve were recorded by using HITACHI model F-4500 fluorescence spectrophotometer with a 400V photomultiplier tube and a 150 W Xe lamp. [pic 1]

Fig.1 shows the X-ray diffraction pattern of the products, which matches the XRD data of standard SrAl2O4(JCPDS:34-379,synthesized at 1500℃) very well. The grain size of the product with this formula is 41.1nm.Besides,the excitation spectrum and emission spectrum peaks shift to shorter wavelength compared with those of the high temperature solid state products(365 and 405 nm). The peak at 345nm shift by 20nm. The decay rate consists of a fast and a slow process, and the persistent time observed in darkness can reach several hours. The tiny difference in the structure of product caused by the different synthesis process may lead to the shift (20 and 4 nm respectively) of excitation and emission peaks of Eu2+. There may be two aspect of reasons to explain this phenomenon: first, because of the quantum effect, the kinetic energy of the electrons increases with the decrease of particle size which leads to larger energy gap, so they need more energy to be excited, that results in the excitation and emission shift to shorter wavelength. Second, the small dimensional effect makes the frequency of bond vibration increase that leads to the excitation and emission shift to shorter wavelength it also proves that the particle size is in nanometer.