Preparation And Luminescence Properties Of Rare Earth Doped Red Phosphors

White LEDs as the fourth generation light source have attracted great research attention due to their numerous advantages, including efficient light output, better reliability, a long lifetime, low power consumption and environmentally friendly features. Up to now, the most popular approach for producing commercial white LEDs is to combine a LED chip with phosphor. The properties of phosphor significantly affect the parameters of white LEDs, such as luminous efficacy, color rendering index, color temperature and lifetime. Especially, the efficiency of red phosphor need to be improved greatly, and the development of novel red phosphor with high efficiency and excellent stability is an urgent and challenging task. The purpose of this paper is to search and develop novel rare earth doped red phosphor and improve their performances.(1) K2Ba(WO4)2:Eu3+ and K2Ba(WO4)2:Eu3+, Cl- were synthesized using solid state reaction method. The effects of Cl- doping on the crystal structure, morphology, and luminescent properties of K2Ba(WO4)2:Eu3+ were investigated in detail. All phosphors exhibit red emission peaking at 615 nm upon 394 nm excitation. Cl- improved the samples’ performances and the optimal concentration was 18 mol%. Unlike the common view, the charge compensation mechanism cannot account for the enhancement of emission intensity. Based on the detail study of the photoluminescence of Cl- doped samples, it can be deduced that the change of the lattice symmetry of Eu3+ sites by the addition of Cl" ions was responsible for the emission enhancement, which resulted the increase of 5D0â†'7F2 transition probability. K2Ba(WO4)2:Eu3+, Cl- phosphors show excellent luminescent properties, suggesting the suitability for white LEDs applications.(2) K2Ba(WO4)2:Sm3+ and K2Ba(WO4)2:Eu3+, Sm3+ were synthesized by solid state reaction method. The phase formation, morphology, luminescent properties, energy transfer and thermal quenching behavior were investigated. Sm3+ exhibit red emission peaking at 560 and 598 nm upon 402 nm excitation and the optimal concentration of Sm3+ was 3 mol%. The concentration quenching mechanism is the multipolar interaction. There was energy transfer between Sm3+ and Eu3+ and the mechanism of energy transfer was proved to be the dipole-dipole interaction. Moreover, K2Ba(WO4)2:Eu3+, Sm3+ show a remarkable thermal stability, indicating that K2Ba(WO4)2:Eu3+, Sm3+ phosphor is a candidate of the red phosphor for white LEDs.(3) Ca14Al10Zn6O35:Dy3+ and Ca14Al10Zn6O35:Dy3+, Mn4+ were synthesized by solid state reaction method. The phase formation, morphology, luminescent properties, energy transfer and thermal quenching behavior were investigated. The energy transfer between Dy3+and Mn4+was firstly observed via the electric dipole-dipole interaction. Ca14Al10Zn6O35: Dy3+, Mn4+ had an excellent resistibility to thermal quenching and the different effect of temperature on the emission intensity of Stokes and anti-Stokes sidebands of Mn4+ was observed. By adding Na+ as a charge compensator, the emission intensity of Ca14Al10Zn6O35: Dy3+, Mn4+ can be enhanced and the color tunability can be achieved. Ca14Al10Zn6O35:Dy3+, Mn4+, Na+ phosphors have potential application in solid state lighting field.(4) RbBaPO4:Ce3+and RbBaPO4 Eu3+ were synthesized by solid state reaction method. The phase structure, luminescent properties and temperature stability were investigated. The spectroscopic data of Ce3+ were calculated in detail. With the increasing concentration of Ce3+, the 5d barycenter declines gradually and a significant red shift can be clearly found from the emission spectra which is illustrated by employing the configurational coordinate. Considering the luminescent properties of RbBaPO4:Ce3+, Ce3+ can be used as sensitizer to improve the luminescence of other rare earth activators. RbBaPO4:Eu3+ exhibit orange-red emission and the optimal concentration of Eu3+ was 9 mol%. The quantum efficiency η was calculated to be 31%. The phosphor show excellent thermal stability and the activation energy ΔE was calculated to be 0.292 eV.