Study Of Structures And Luminescent Properties Of Sr₄Al₁₄O₂₅:Mn⁴⁺ Red Phosphor Affected By Cationic Doping

The absence of high-performance oxide red phosphors has restricted the application and development of warm white light-emitting diodes(WLEDs).A series of Mg2+,Na+ and Li+ doped Sr4Al14O25:Mn4+ red phosphors were synthesized by a high-temperature solid-phase method and the characteristics such as phase structure,microstructure,luminescence properties,and thermal quenching mechanism were studied.The results showed that these phosphors exhibit good luminescence performance and high thermal stability,and could be used in warm-white LEDs.The main research content and results are as follows:(1)A series of divalent cation-doped(Mg2+)oxide red phosphors Sr4Al14O25:Mn4+ were successfully synthesized by a high-temperature solid-phase method.The theoretical calculation,structure,and luminescence properties of Sr4Al14O25:Mn4+ phosphors were systematically studied by changing the synthesis temperature and the amount of Mg2+ doping.The theoretical calculation and experimental results showed that Mg2+ can increase the photoluminescence(PL)intensity and thermal quenching performance of SAO:Mn4+.Mn4+ emits red light only in the Sr4Al14O25 structure,not in the Sr Al2O4 structure.Structural analysis showed that pure-phase Sr4Al14O25 was obtained at 1250℃,while impure-phase Sr Al2O4 appeared at 1300℃.The optimal Mg2+ doping concentration was Mg2+/Mn4+=1:1 and the maximum PL intensity occurred at Mn4+ doping concentration of 0.5 mol%.The phosphors exhibited excellent water resistance and acceptable thermal stability.The WLED device encapsulated with the prepared SAO:Mn4+,Mg2+ and commercial YAG:Ce3+ yellow phosphors showed a relatively low correlated color temperature of4737 K,a high color rendering index of 81.7,and an emission efficiency of 153.61 lm/W under a60 m A driving current.(2)One-valence Na+ doped oxide red phosphor of Sr4Al14O25:Mn4+(SAO-Mn)was prepared.The theoretical calculations,structure,and luminescent properties of S Sr4Al14O25:Mn4+ phosphors were systematically studied by varying the doping amount of Na+.Theoretical calculations and experimental results show that the Na-Mn co-doped system has a more stable structure.The Mn4+possibly occupies the octahedral Al1 site and the possibility of simultaneously substituted position of Al1 and Al2 sites(octahedral)is greater.The calculation results also show that Na+ significantly increases the luminescence intensity and thermal quenching resistance,and the red emission only comes from Mn4+ occupying the octahedron.With the increase of Na+ doping amount,the PL intensity of SAO-Mn first increases and then decreases,and 0.5 mol is the optimal value.Compared with the PL intensity of SAO-Mn at 150℃,the intensity of SAO-0.5Na,Mn increased by about 200%,and the fitted thermal activation energy is 0.84 e V.The fluorescence lifetime continuously decreases with the increase of Na+ content.The 0.5 mol Na+ doped sample is a pure phase and has a good morphology.Using the prepared SAO-Na,Mn and YAG:Ce3+ phosphors encapsulated WLED device,the correlated color temperature is 4085 K,color rendering index is89,and luminous efficiency is 137.12 lm/W at a driving current of 150 m A.(3)A monovalent Li+ doped oxide red phosphor Sr4Al14O25:Mn4+,0.4Li(SAO-0.4Li)was prepared,and the theoretical calculation,structure and luminescent properties of Sr4Al14O25:Mn4+phosphors were systematically studied by changing the doping amount of Li+.The theoretical calculation results showed that Li+ is more inclined to occupy the interstitial site.The structural study showed that with the introduction of Li+,the diffraction angle of about 33.5° first moved towards larger angles,and then towards smaller angles.The result is due to the compensating effect of charge when the concentration of Li+ was low,and the substitution effect when the concentration was high.The PL intensity of SAO-0.4Li first increased and then decreased.The Li+optimal concentration is 0.5 mol.The fluorescence lifetime continued to decrease with the increase of Li+ content.The sample doped with 0.4 mol Li+ was pure phase and had a good morphology.A WLED device encapsulated with SAO-0.4Li and YAG:Ce3+ phosphors showed a correlated color temperature of 4667 K,a color rendering index of 82,and a luminous efficiency of 137.34 lm/W at a driving current of 20 m A.