The Synthesis And Luminescence Properties Of Eu³⁺-Doped Borate And Phosphate

In recent years, white light-emitting diodes (W-LEDs) have become the most efficient potential light sources for applications in solid-state lighting. W-LEDs have attracted substantial attention because of their extraordinary luminous efficiency, excellent longevity, low power consumption, good reliability, and environmental friendliness. Therefore, W-LEDs are considered as an indispensable solid-state light source that can replace other light sources, such as tungsten light bulbs and fluorescence lamps. Currently, the combination of yellow phosphors (YAG:Ce3+) and InGaN-based blue diode is the most popular and conventional method to generate W-LEDs because of their simplicity of fabrication and maturity of processing. However, the type of W-LED created by this conventional method has a thermal quenching problem and a poor color rendition. As an alternative, white light can be obtained by combining a UV chip with red, green, and blue phosphors. Therefore, high efficient and stable red phosphors materials are significant in producing W-LEDs. Traditional phosphors usually based on the aluminate, silicate and sulfide. In recent years, the rare-earth doped borate and phosphate have attracted much attention.Aimed at seek high efficient and stable red phosphors, several Eu3+-doped borate and phosphate phosphors were successfully synthesized by a solid-state reaction in this study. Techniques such as X-ray power diffraction, scanning electron microscopy and photoluminescence spectra (PL) were used to characterize the phosphors, and the crystal structure, morphology and luminescence properties of these phosphors were studied. In addition, the effect of factors, such as activator Eu3+and co-activator Bi3+, on the luminescent properties of these phosphors were also studied. The main works were contained as below:(1)LiMgBO3:Eu3+and LiZnBO3:Eu3+phosphor were successfully synthesized at750℃and900℃, respectively. Upon excitation by near ultraviolet and blue light, the LiMgBO3:Eu3+phosphor exhibits intense red emission at615nm, corresponding to the forced electric dipole5D0â†'7F2transition of the Eu3+ions; the LiZnBO3:Eu3+phosphor exhibits intense red emission at591nm, corresponding to the magnetic dipole transition5D0â†'7F1transition of the Eu3+ions. Furthermore, co-doping the LiMgBO3:Eu3+phosphor with the sensitizer Bi3+effectively extends the absorption strength of7F0â†'5L6and7F0â†'5D2transitions, caused by the wide absorption band of Bi3+, and the quadripole-quadripole interaction is the major energy transfer mechanism in LiMgBO3:Eu3+,Bi3+phosphors.(2)KBaY(BO3)2:Eu3+phosphor was successfully synthesized at920℃. Upon excitation by near ultraviolet and blue light, the KBaY(BO3)2:Eu3+phosphor exhibits intense red emission at591nm, corresponding to the magnetic dipole transition5D0â†'7F1transition of the Eu3+ions. Furthermore, The enhancement in the luminescence intensity of KBaY(BO3)2:Eu3+, Bi3+phosphor due to the addition of Bi3+ions indicates energy transfer from Bi3+to Eu3+, and the dipole-uadripole interaction is the major energy transfer mechanism in KBaY(BO3)2:Eu3+, Bi3+phosphors.(3)NaCaPO4:Tb3+,Eu3+phosphor was synthesized at900℃. The luminescence properties and the decay curves supported the occurrence of energy transfer from Tb3+to Eu3+ions. The energy transfer mechanism was studied and demonstrated to be a quadrupole-quadrupole interaction. This energy transfer induced a change in the emitted color of the phosphors from green to yellow, which can be obtained by appropriately tuning the Eu3+concentration.