Study On Preparation And Properties Of Dy And Er Co-doped Lanthanum Aluminate Luminescent Materials

LaAlO₃is a simple perovskite type oxide of ABO₃type.It is also an indirect semiconductor with wide band gap and excellent chemical thermal stability.The A-site and B-site can be doped with different elements to improve the properties of the system.At the same time,rare earth ions have abundant energy level transitions,which make it possible to prepare phosphors emitting different colors.At present,the most studied phosphors are Eu³⁺,Ce³⁺,Yb³⁺,etc.,but there are few studies on single doping Dy³⁺and Er³⁺with lanthanum aluminate as the main phase.Therefore,this paper selects lanthanum aluminate as the matrix material to prepare pure lanthanum aluminate and modified lanthanum aluminate at different temperatures by solution combustion method The phase composition,morphology,elemental composition and luminescent properties of lanthanum aluminate were studied.LaAlO₃,La_1-xDy_xAlO₃,La_1-yEr_yAlO₃and La_1-x-yDy_xEr_yAlO₃were synthesized by solution combustion method with lanthanum nitrate,aluminum nitrate as reducing agent,glycine and mannitol as oxidants,dysprosium nitrate and erbium nitrate as the sources of rare earth ions.The final samples were analyzed by X-ray diffraction,scanning electron microscopy,ultraviolet visible absorption spectroscopy,X-ray photoelectron spectroscopy and fluorescence spectroscopy.The effects of calcination temperature,choice of combustion agent and doping ion concentration on the special lattice parameters and luminescent properties of the products were analyzed.The results are as follows:（1）Firstly,the pure LaAlO₃was prepared by solution combustion method at 700℃with the molar ratio of La（NO₃）₃·6H₂O:Al（NO₃）₃·9H₂O:C₂H₅NO₂=3:3:10.The results show that the crystallite size is 27.64 nm,the crystallinity is 78.82%,the particle has good dispersion and clear outline,there is absorption in the ultraviolet visible region,the band gap width is 5.44 e V,and there are oxygen holes and oxygen adsorption in the system It can be used as luminescent matrix.（2）The La_0.97Dy_0.03AlO₃was prepared at 800℃by adding Dy（NO₃）·6H₂O to LaAlO₃-C₂H₅NO₂at 700℃.The results show that La_0.97Dy_0.03AlO₃is still hexagonal,with a crystallinity of 91.94%.The particles are finer,well-developed and rod-shaped.The absorption of the ultraviolet visible region is enhanced,the band gap width is reduced to 4.98e V,and the strongest emission peak is around 423 nm.With the increase of Dy³⁺doping concentration,the peak position appears blue shift,and the La/Al ratio becomes smaller,which indicates that Dy³⁺replaces part of La³⁺.（3）The La_0.97Er_0.03AlO₃was prepared at 800℃with LaAlO₃-C₆H₁₄O₆as the main phase and Er（NO₃）₃·6H₂O as the additive.The crystallinity of La_0.97Er_0.03AlO₃was 81.41%and the crystallite size was 27.17 nm.The grains were closely arranged and rod-shaped.The absorption of ultraviolet visible region was enhanced and the band gap width increased.With the increase of concentration,the peak position did not move,but the luminescence intensity showed a trend Therefore,the quenching concentration is 0.03.（4）The La_0.97Dy_0.03Er_0.03AlO₃prepared at 900℃with LaAlO₃-C₂H₅NO₂as the main phase,Dy（NO₃）₃·6H₂O and Er（NO₃）₃·6H₂O as the additive.The La_0.97Dy_0.03Er_0.03AlO₃is still hexagonal,the crystallinity is 88.90%,the crystallite size is 27.07 nm,the size is uniform,well dispersed,spherical,the range of absorption edge is expanded,the band gap width is reduced by 0.37 e V,and the La/Al ratio is close to the pure phase,which indicates that La³⁺may be partially removed by Dy³⁺and Er³⁺.With the increase of Er/La ratio,the luminescence intensity increases gradually,which is due to the sensitization of Er³⁺to Dy³⁺.