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Preparation and Luminescent Properties of Rare Earth Doped Borate Phosphors

Author: YangFan
Tutor: LiangYuJun
School: China University of Geosciences
Course:
Keywords: White LEDs Phosphor Borates
CLC: TN104.3
Type: Master's thesis
Year: 2013
Downloads: 25
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Abstract


White light-emitting diode (W-LED) has attracted great attentions due to advantages of high efficiency, energy saving, long lifetime, environment protection. Currently, the commercial method for fabrication of white LED is to combine a blue LED chip with yellow-emitting yttrium aluminum garnet (YAG:Ce). However, YAG:Ce phosphor cannot properly meet the requirement of illumination resource with low color rendering index (CRI) due to the lack of red component in the emission spectrum. So it is highly desirable to develop novel stable phosphor for white LED. Borates as a kind of luminescent host have been widely studied due to high thermal, chemical stability, simple synthesis process and strong absorption in the near ultraviolet region.In this work, we reported three new borate phosphors via solid state reaction which aim at rare types of borate phosphors and few application in white LED. In the meantime, we investigated systematically the synthesis process, crystal structure, photoluminescence properties and energy transfer mechanism. The main contents are listed as follows:1. A series of NaSrBO3:xEu3+and NaSr1-2xBO3:xEu3+, xM+(M=Li, Na, K) phosphors were synthesized by the solid state reaction. The crystal structure, photoluminescence properties and concentration quenching of NaSrBO3:Eu3+phosphors were systematically investigated. The excitation spectra indicate that the phosphors can be efficiently excited by394nm, which is matched well with the emission wavelength of near-UV LED chip. All the samples show the characteristic red emission of Eu3+ions (5D0→7FJ, J=0,1,2,3and4). The maximum intensity of luminescence is observed at the Eu3+concentration around x=11. The concentration quenching of Eu3+in NaSrBO3:Eu3+phosphor can be mainly attributed to quadrupole-quadrupole interaction. The relative emission intensities of Eu3+(5Do→7F2) in NaSrBO3:Eu3+phosphors with Li+, Na+or K+introduced as charge compensator are significantly enhanced, and the phosphors added with K+ions show the strongest emission. The emission intensities of NaSr1-2xBO3:xEu3+, xM+(M=Li, Na, K) are about1.47,1.64, and2.08times than that of commercial red phosphor Y2O2S:Eu3+. These results indicate that NaSr1-2xBO3xEu3+, xM+(M=Li, Na, K) phosphors exhibit potential applications in the field of near-UV LED as an efficient red-emitting phosphors.2. A novel green phosphor NaSrBO3Tb3+, Li’was synthesized by the solid state reaction. The crystal structure, photoluminescence properties and concentration quenching of NaSrBO3:Tb3+, Li+phosphor were systematically investigated. The phosphor shows monoclinic structure and the optimal Tb3+concentration in NaSrBO3:Tb3+, Li+is6mol%. The phosphor presents bright green emission centered at542nm corresponding to5D4→7F5transition of Tb3’ions under the ultraviolet excitation of378nm. The concentration quenching mechanism can be mainly attributed to the quadrupole-quadrupole interaction. The present work suggests that NaSrBO3Tb3+, Li+phosphor is a potential green-emitting phosphor for UV LEDs.3. Eu3+-activated Ca2BO3Cl with different charge compensation approaches were synthesized by the solid state reaction method, and systematically characterized by photoluminescence excitation and emission spectra, concentration quenching and CIE1931chromaticity coordinates at room temperature. All the samples show the characteristic red emission of Eu3+ions with good CIE chromaticity coordinates. The relative emission intensities of Eu3’(5D0→7F2) in Ca2BO3Cl:Eu3+phosphors with Li, Na, K. introduced as charge compensators are enhanced about2.1,1.6and1.5times than that of direct charge balanced. Such difference is considered to be due to the different ion radii effect on the spin-orbit couplings and crystal field of Eu3+ions. These results show that Ca1-1.5xBO3Cl:Eux3+, Ca1-2xBO3Cl:Eux3+, Mx (x=0.04, M=Li, Na, K) phosphors exhibit potential applications in the field of solid state illumination.4. Tm3+and Dy3+co-doped YAl3(BO3)4phosphors were synthesized by the solid state reaction method. The phosphors show blue emission band centered at450nm originated from the transition of Tm3’ions and yellow band of573nm ascribed to Dy3+ions excited by UV light. The emission colors are tuned from blue to white and ultimately to yellow through concentration variation of luminescent centers of Tm3+and Dy3+in YAl3(BO3)4phosphors. A white light can be achieved from YAl3(BO3)4:0.03Tm3+,0.09Dy3+phosphor with chromaticity coordinates of (0.310,0.331) under excitation at365nm. The results show that the single-phased YAl3(BO3)4:Tm3+, Dy3+phosphors are a potential phosphors for current illuinated light source.

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