Study On Preparation Process Of MgAl₂O₄ By Hydrothermal Method And Its Eu-doped Luminescence Properties

MgAl₂O₄ powders and Eu³⁺ion single-doped MgAl₂O₄ phosphor were synthesized by hydrothermal method in this paper.Scanning electron microscope（SEM）,X-ray diffraction（XRD）,F-7000 fluorescence spectrometer,etc.were used to characterize the microscopic morphology,phase structure and luminescence characteristics of the product.Optimal process conditions under the constraints of various experimental factors such as the reaction temperature,raw materials ratio and mineralizer were also discussed.The photoluminescence performance and energy transfer mechanism of the material can be further mastered by adjusting the doping amount.The main research results of this paper are as follows:（1）In order to lay the foundation for the next step of activating ion doping the optimal process parameters of the MgAl₂O₄ matrix material are determined by adjusting the hydrothermal temperature,hydrothermal time,raw material ratio and other conditions.The obtained optimal condition is that when the molar ratio of Mg²⁺to Al³⁺in the solution is 1:2,gibbsite is used as the aluminum source,and ammonia is used as the precipitant to adjust the p H of the solution to 11 and the hydrothermal temperature at 200℃for 6 h.The essence is to obtain the precursor of the hydrotalcite phase and theγ-Al OOH phase with high activity which is beneficial to the subsequent calcination.The crystallinity of the calcined product increases with the increase of the calcining temperature（1000℃～1200℃）.The morphology growth of the calcined product inherits the morphology of its precursor.It is mixture morphology with irregular flaky and hexagonal plate which is about 1.2μm long and 500 nm wide.When a molar ratio of F^-to O^2-reached 1:1 in the solution by adding the mineralizer AlF₃ or Na BF₄,MgAl₂O₄samples with octahedral morphology are obtained after calcination.（2）A series of Eu³⁺doped Mg_1-xAl₂O₄:x Eu³⁺micron particles were synthesized by hydrothermal method.The analysis shows that when Eu³⁺doping does not exceed 4 mol%,it enters the lattice of the matrix material,still maintains the spinel structure,and presents multi-contour plate-like particles with good dispersion and uniform morphology.Under excitation of249 nm and 395 nm wavelengths of Mg_1-xAl₂O₄:x Eu³⁺（x=1.0-4.0,mol%）,the emission peaks of Eu³⁺at 578 nm,593 nm,618 nm,654 nm and 702 nm can be observed.And when the Eu³⁺concentration x≤3%,the luminous intensity of the sample increases monotonously with the increase of Eu³⁺doping concentration.Under the premise of ensuring a single crystal phase,the maximum amount of Eu³⁺doped is less than 4%.Based on the Judd-Ofelt theory,within the studied concentration range（1.0-4.0 mol%）,Eu³⁺ions in the crystal lattice occupy both symmetrical and asymmetrical positions.Most Eu³⁺is in a crystal lattice environment with strong asymmetrical properties.That is,the interstitial position of MgO tetrahedron,but with the increase of Eu³⁺ion doping concentration,the occupied position changes.In addition,with the increase of Eu³⁺ion doping,the average lifetime of the 5D⁰ energy level gradually shortened,indicating that there is a non-radiative energy transfer between O^2-and Eu³⁺in Mg_1-xAl₂O₄:x Eu³⁺.The CIE color coordinates of samples doped with different concentrations of Eu³⁺are all located in the red light region,which has certain value for the application of Mg_1-xAl₂O₄:x Eu³⁺phosphors in optics and other fields.