Synthesis And Luminescence Properties Of Mn⁴⁺-doped Luminescent Materials

At present,the main way to obtain white light LED is to use the principle of complementary color to excite the blue LED chip to excite the YAG yellow phosphor.However,due to the lack of red light components in the spectrum,the white light displayed often has a high color temperature（CCT>4500 K）and a low color rendering index（R_a<80）,which limits the application of LED in indoor lighting,store lighting and other directions.The study found that the role of red light is more than that.The photosynthetic pigments and phytochromes in plants can efficiently absorb light in the red band,and P_fr can absorb far-red light above 700nm.Based on the above background,this paper explores Mn⁴⁺-doped red light-emitting materials.The experimental results are as follows:（1）The preparation method and luminescence properties of BaZrGe₃O₉:Mn⁴⁺were mainly studied.By analyzing the crystal structure of the matrix,it was concluded that Mn⁴⁺was replaced by Zr⁴⁺.The excitation and emission spectra were characterized.It was confirmed that there are two excitation peaks at 294 nm and 435 nm.Under the excitation at 435 nm,the emission peak was located in the red light region of 667 nm,which matches the blue LED chip.The effects of the concentration of the activator Mn⁴⁺on the emission intensity and luminescence lifetime were experimentally studied,and it was determined that the optimal doping concentration was 0.2 mol%,and the concentration quenching was caused by the electric dipole-electric dipole interaction.In order to explore the thermal stability of luminescent materials,the emission spectrum and luminescence lifetime in the temperature range from low temperature 80 K to high temperature 550 K were tested.The results showed that the emission intensity of luminescent materials was greater at low temperature.As the temperature increased,luminescence lifetime and emission intensity were reduced.The activation energy was 0.473 e V,the color purity was as high as 97.4%,and it had great application prospects in warm white LEDs.（2）Ba₂MgWO₆:Mn⁴⁺red light-emitting material was prepared by solid-phase method.There were four characteristic excitation peaks in the range of 250-600 nm.Under the excitation of 340 nm,it exhibited asymmetric narrow-band red light emission,and the emission peak was located at 720 nm.The light in this band was far-red light suitable for the absorption of plant phytochrome P_fr,which proved that this luminescent material had great potential in plant lighting applications.When the concentration of Mn⁴⁺reached 0.5 mol%,the emission intensity was the strongest.With the increase of the concentration of Mn⁴⁺,the emission intensity decreases,but the luminescence lifetime did not change significantly.Experiments show that the addition of the charge compensator K⁺can significantly enhance the luminescence,and the luminescence lifetime decreases regularly with the increase of Mn⁴⁺concentration.The optimal doping concentration was determined to be Ba₂MgWO₆:0.5 mol%Mn⁴⁺,10 mol%K⁺.On this basis,the thermal stability of the sample was investigated.With the increase of temperature,the emission intensity and luminescence lifetime of the luminescent material decreased.（3）The valence problem of Mn-doped luminescent materials was explored.Because Mn⁴⁺had excellent luminescent properties in oxyfluoride matrix,oxyfluoride K₂Nb O₃F was prepared experimentally.This material had a suitable crystal field environment for the presence of Mn.In the six-coordination environment,Mn was still difficult to form Mn⁴⁺.Further exploration found that Mn⁴⁺had a strong self-reduction property,and it was easy to form Mn²⁺spontaneously.However,Mn²⁺was affected by the crystal field environment,showing luminescence from green to orange-red.Summarizing the experimental results,it was given under what circumstances will lead to the failure of the experiment of Mn⁴⁺-doped luminescent materials.