Controllable Preparation Of Cryolite Structure Compounds

At present,the main problem to be solved in the research and application of up-conversion luminescent materials is to find new host crystals with low phonon energy,good optical transparency,stable performance,and favorable for rare earth ion energy transfer.The cryolite structure compound has low phonon energy and good optical transparency,which is expected to provide a better structural environment for rare earth ion doping and energy transfer and become a new upconverting luminescent material matrix with excellent performance.In this dissertation,three kinds of cryolite structural compounds were successfully synthesized by hydrothermal method.They were monoclinic Na₃AlF₆,Na₃GaF₆ and cubic?NH₄?₃AlF₆.The effect of experimental conditions on the structure and morphology of the cryolite structural compounds were studied.The regulation of morphology and particle size of the cryolite structural compounds were achieved.The main conclusions are as follows:1.The monoclinic Na₃AlF₆ pure phase was synthesized by the hydrothermal method,and the influence of the synthesis conditions on the morphology and crystal grain size was studied.The results showed that changing the reaction temperature could increase the average grain size of Na₃AlF₆ from 150 nm to 250 nm,and the morphology was irregular and granular;decreasing the pH of NaF solution could effectively regulated the morphology of Na₃AlF₆,from irregular granular to dendritic and block,grain size increased from 150 nm to 2?m;when the reaction solvent was water-ethanol and water-ethylene glycol system,the average grain size of prepared Na₃AlF₆ was about 50 nm and 100 nm,respectively;cetyltrimethylammonium bromide and dodecylsulfuric acid could inhibit Na₃AlF₆,the Na₃AlF₆ crystals were grown to have a particle size of 50nm to 100 nm.2.The pure phase of cubic?NH₄?₃AlF₆ was synthesized by hydrothermal method,the influence of the synthesis conditions on the morphology and crystallite size was studied.The results showed that the average grain size of?NH₄?₃AlF₆ increased from200 nm to 350 nm when the reaction temperature was increased and the reaction time was prolonged;the pH of the reaction solution increased from 4.5 to 6,the average grain size of?NH₄?₃AlF₆ decreased from 300 nm to 150 nm;the morphology of the octahedron was destroyed and perforation occurred,when the reaction solvent was water-ethanol and water-ethylene glycol system,the average grain size of?NH₄?₃AlF₆was about 250 nm and 400 nm,respectively.3.The hydrothermal synthesis experiment of Na₃AlF₆-?NH₄?₃AlF₆ isomorphous series was carried out.The results showed that Na and NH₄ could be used as a limited substitute.When NH₄ was substituted for Na less than 60%,the product was a monoclinic?Na,NH₄?₃AlF₆ phase;When Na was substituted for NH₄ less than 10%,the product was a cubic?NH₄,Na?₃AlF₆ phase;when NH₄ replaced Na more than 60%or Na replaced NH₄ more than 10%,the product was in the two-phase coexistence of cubic?NH₄,Na?₃AlF₆ and monoclinic?Na,NH₄?₃AlF₆.4.The monoclinic Na₃GaF₆ pure phase was synthesized by hydrothermal method.The influence of the synthesis conditions on the morphology and crystallite size was studied.The results showed that the average grain size of Na₃GaF₆ increased from 350nm to 1?m when the reaction temperature was increased and the reaction time was prolonged,the average grain size of Na₃GaF₆ prepared from pure ethanol system was about 80 nm,the average grain size of Na₃GaF₆ prepared by the mixed system of ethanol and water was 200 nm,the average grain size of Na3GaF6 prepared by the pure water system was the largest,about 600 nm.