Material Design On Li_xNa_1-xYF₄ Doped With Er³⁺/YB³⁺ Upconversion Material And Preparation

Photon up-conversion?UC?is a process in which the sequential absorption of two or more photons leads to the emission of light at shorter wavelength than the excitation wavelength.It is an anti-Stokes type emission.Materials that can achieve this process are called up-conversion materials.Rare earth ions are widely used in the field of up-conversion luminescence materials for their rich energy level.There are many 4f orbital electrons which are shielded by outer electrons.Up-conversion material can convert the infrared light that cannot be utilized by cell into visible light that can be utilized,thus increasing the efficiency of solar cell.Compared different concentration of Er³⁺ doped LiYF4 through the first principle study.It is found that the introduction of Er³⁺ ions makes the lattice parameters smaller.With increasing concentrations of Er³⁺ ions,the stability of systems have improved.And density of states as a whole move to the direction of lower energy level.As to absorption,the system doped with 6.25% Er³⁺ ions absorb more than the concentration of 12.5% and 18.75% in range of 1000-2000 nm.And the system all have low reflectivity in infrared light.Synthesis Li_xNa_1-xYF₄: Er³⁺/Yb³⁺ with hydrothermal method and the samples are all pure ?-NaYF4 and the crystalline are all perfect with good dispersion and complete appearance.They all have bright luminescence,white and green,under the pump of 808 nm and 980 nm,even can be seen by naked eyes.When the concentration of Er³⁺ ions is 25%,the sample powder is most luminous under the 808 nm pump.At the same time,when the concentration of Er³⁺ ions reaches 50%,the sample powder is most luminous under the 980 nm pump.As the result of sensitization effect from Yb³⁺ ions,the luminescence under the 980 nm pump is much more than under the 808 nm pump.