SrB4 O7 : Eu磷光粉的制备及其发光性能

采用高温固相法合成了SrB₄O₇ : Eu荧光粉,并研究了不同原料、掺杂浓度、煅烧温度等因素对其发光性能的影响。发射光谱测试结果表明:SrB₄O₇ : Eu荧光粉的最佳Eu掺杂浓度为2%左右,进一步增大掺杂浓度会导致浓度猝灭。煅烧温度对基质组成影响较大,随着温度的升高,基质中BO₄四面体所占比例增大,有利于Eu³⁺离子的还原。以水合硼酸锶为原料制得样品的发光强度高于以SrCO₃和H₃BO₃为原料制得样品的发光强度。

Synthesis and Luminescent Properties of SrB4O7:Eu Phosphors

In recent years, the borate-based phosphors have attracted great interest due its easy synthesis, low preparative temperature and high fluorescent yields. Many borates which contain BO₄ group have attracted more and more attention, because the tetrahedral structure of BO₄ can restrain the oxidation of divalent rare-earth ions. The typical representations of better borate matrix are SrB₆O₁₀, Sr₂B₅O₉X(X=Cl, Br) and SrB₄O₇. Strontium borate phosphors are usually synthesized by traditional solid state reactions by using SrCO₃ and H₃BO₃ as raw materials. However, less attention has been paid to the influence of synthesis route on the final performance of the products. In this work, SrB₄O₇DK(]∶DK)]Eu phosphors were prepared using hydrated strontium borates(SrB₂O₄·4H₂O and SrB₆O₁₀·5H₂O) as raw materials. The effect of doping concentration and post-calcining temperature on the luminescence properties was studied. It was found that Eu ions with two oxidation states (+2 and +3) coexist in the SrB₄O₇ host. The emission spectrum shows that the main emission peak located at 367 nm, which is attributed to Eu²⁺ ions transition from 4f⁶5d to 4f⁷(⁸S_7/2). The emission peaks of Eu³⁺ ions located at 588, 600, 614, 651 and 700 nm corresponding to the transitions ⁵D₀→⁷F₀, ⁵D₀→⁷F₁, ⁵D₀→⁷F₂, ⁵D₀→⁷F₃, ⁵D₀→⁷F₄ respectively. Among them, the dominant emission is the electric-dipole transition ⁵D₀→⁷F₂, indicating that the Eu³⁺ ion occupies asymmetrical center in lattice.
The emitting intensity mainly depends on the amount of luminescence center which is relate to the doping concentration. The emitting intensity increases to a maximum with the increment of doping concentration, and then it decreases because of concentration quenching. When the Eu concentration is about 2%, the maximum of emitting intensity occurs. Post-calcining temperature influences on the chemical structure form of resultant powder. SrB₂O₄, SrB₆O₇ and SrB₄O₇ are formed when the post-calcining temperature is lower than 900 ℃. In these borates, SrB₂O₄ contains only triangular BO₃ groups, SrB₄O₇ contains only tetrahedral BO₄ groups, and SrB₆O₁₀ contains both the BO₃ and BO₄ groups. As the temperature elevates, the proportion of SrB₄O₇ increases and the single phase of SrB₄O₇ can be obtained at 900 ℃. As a fact that the BO₄ groups can stabilize the divalent rare-earth ions to avoid oxidation, so that more Eu³⁺ ions can be reduced to be Eu²⁺ ions and the emission intensity would increase. It was also found that the emission intensity from the sample synthesized using hydrated borates is higher than that from the sample synthesized by traditional route.