Study On The Preparation And Properties Of Er³⁺/Yb³⁺ Doped Aluminate CaLnAlO₄（Ln=Y,Gd,La）upconversion Phosphors

Lanthanide ion-doped upconversion luminescent materials have been widely used in temperature sensing,optical anti-counterfeiting,and nano-biomarkers due to their unique luminescent properties.However,the luminescence properties of upconversion luminescent materials are greatly influenced by the matrix materials,and the co-doping of Er³⁺/Yb³⁺ions in different matrices has brought great difficulties to improve the upconversion luminescence properties.Therefore,it is important to clarify the main factors affecting the upconversion luminescence performance of Er³⁺and Yb³⁺ions for the practical application of the materials.Therefore,in this thesis,the aluminate Ca YAl O₄,Ca Gd Al O₄ and Ca La Al O₄（CYA,CGA and CLA）substrate materials of the same crystal system and space group were selected,and the doping concentration of the samples was determined to be 2%Er³⁺/10%Yb³⁺by considering the Er³⁺/Yb³⁺ion emission of the three substrates at different concentrations.The structural composition and luminescence properties of the materials were studied,and the influencing factors of the upconversion luminescence properties were investigated in detail,and the main work and conclusions are as follows:（1）Er³⁺/Yb³⁺ion co-doped CYA,CGA and CLA phosphors were prepared by high-temperature solid-phase method.The results of XRD and Rietveld refinement showed that Er³⁺/Yb³⁺ions would preferentially occupy the lattice sites of rare earth ions and the main lattice structure of the crystals did not change before and after doping.Combined with the XPS mapping and EDS energy spectrum results it was determined that Er³⁺and Yb³⁺ions have been effectively doped into the matrix material.From the SEM and TEM results,it can be seen that there is no significant difference in the morphology of the three samples,and the particle size distribution is around 20μm range.With the increase of excitation power,the red light emission intensity of Er³⁺ions increases more obviously than that of green light.The red-green light emission of Er³⁺ions in all three substrates completed the energy level jump through a two-photon process.（2）The Raman and red emission spectra show that phonon energy is not the main factor making the difference in the upconversion luminescence properties.The relationship between the average distance between the adjacent sites replaced by ions and the red-green ratio（R/G）ratio is a quadratic function,the size of the distance will directly affect the shape of the spectrum,within a certain extent,the distance between the sites replaced by rare-earth ions increases,the R/G ratio increases.The larger distance between rare earth ion substitution sites in CLA during energy transfer also makes the electron leap biased toward the red light emission path.Factors such as the crystal field strength and the degree of distortion of the Al-O octahedron disrupt the forbidden electron leap within the 4fⁿ grouping of Er³⁺,making the luminescence intensity the smallest in the CLA and the largest in the CGA.Compared with the magnitude of the band gap value in the energy band structure,the density of states distribution has more influence on the upconversion luminescence performance,and the difference of density of states distribution in the substrate may make the luminescence performance different between them.In addition,to verify the relationship between the distance between adjacent substitution sites and the R/G ratio,the Sr La In O₄（SLI）substrate doped with the same concentration of Er³⁺/Yb³⁺ions was selected,and the quadratic relationship equation was still obtained by co-fitting the data related to three substrates,CYA,CGA and CLA.The synthesized Sr La In O₄:2%Er³⁺/10%Yb³⁺fluorescence has 85.22%red light purity and is expected to be used in applications such as handprinting and labeling.