Cd²⁺-doped NaLuF₄:Yb,Er And Core-shell Enhanced Upconversion Luminescence

Rare earth doped upconversion nanoparticles are favored for their advantages such as large penetration depth,backgroundless fluorescence,and stable luminous properties,especially in the field of biomedicine.Because it is more suitable for imaging in vivo than traditional organic dyes and quantum dot fluorescent materials,a lot of research has been carried out on the composition structure,fluorescence properties and physicochemical properties of upconverted nanoparticles.At present,the most researched is the AREF₄(A is an alkali metal ion,RE is a trivalent rare earth ion)series,and the representative of which is now recognized as the highest fluorescence quantum yield and the best luminous performance of Na YF₄,and the other Transformed nanoparticles have been studied less frequently.For the purpose of enriching the upconversion luminescence system and discovering new luminescence methods,this paper selects a NaLuF₄ matrix that also has research potential,and conducts a series of researches around it.In this paper,Cd²⁺-doped NaLuF₄:Yb,Er nanocrystals were synthesized by an improved high-temperature thermal decomposition method.The effects of Cd²⁺ions on crystal phase formation and luminous intensity were studied.The first principle principle CASTEP software was used to simulate the calculation formation energy at doping concentration.The results show that as the doping concentration increases,the formation energy of the?phase increases,which makes the?phase difficult to form.The experimental results also prove that it is difficult to form the?phase again when the concentration exceeds 12 mol%.With a doping concentration of 6 mol%,a pure?phase with an average size of 23 nm was synthesized,and the fluorescence intensity was increased by 2.6 times compared to the undoped Cd²⁺ion sample,and the emission intensity of red and green light increased by 2.6 times and 2.2 times.In addition,we also found that the incorporation of Cd²⁺ions changed the green/red emission ratio.When the concentration was low,the green/red ratio increased slightly with the increase of the doping concentration.The ratio then decreases and the total luminous intensity decreases.When the volume ratios of the dispersants Span80 and Tween80are 1.2 m L:0.3 m L and 0 m L:1.5m L,the pure?phase can be obtained.When the volume ratio of the two is 1.2 m L:0.3 m L,nanocrystals with good dispersibility can be obtained,the degree of crystallinity is higher,and the crystal shape is a regular hexagon.When using 1.5 m L of Tween80 dispersant alone,better dispersibility can be obtained,but the crystallinity is relatively reduced.NaLuF₄:20% Yb,2% Er,6% Cd nanocrystals was coated with SiO₂ to form a core-shell structure,and then the core-shell structure nanocrystals were co-cultured with mouse osteoblasts.The experimental results show that when the concentration is lower than 50?g/m L,the core-shell structure nanocrystals are basically non-cytotoxic,and even at lower concentrations,they show the effect of promoting cell proliferation.Due to the passivation of surface defects,the coated nanoparticles have a higher luminous intensity than the naked core nanoparticles,and the total fluorescence intensity is increased by 2.4 times.Under the premise of ensuring that the fluorescence intensity is not weakened,the biocompatibility concentration of the composite nanocrystals formed by NaLuF₄:20%Yb,2%Er,6%Cd@SiO₂ and carboxymethyl chitosan is increased to 50?g/m L,which lays the foundation for the combination of up-converting nano fluorescent material and hydroxyapatite to detect bone repair and metabolism in vivo.