Research On The Synthesis And Luminescent Properties Of Ca₃Si₂O₇-based Red Phosphor For Warm White LEDs With High Color Index

With the rapid development of LED industry, there is an increasing demand for the phosphorsused in white LEDs. Accordingly, the preparation and properties of phosphors have attracted intensiveattention. To meet the requirements of interior lighting, high-performance red phosphors for whiteLEDs have become a hot spot in this research area. Apart from nitride phosphors, the newlydeveloped Ca₃Si₂O₇based red phosphor has become one of the most promising fluorescent materialsfor white LEDs application due to its advantage of easy preparation.In this paper, pure Ca₃Si₂O₇samples were successfully synthesised via a high-temperature solidstate reaction method with H₃BO₃adding as a flux. The luminescent properties of Eu²⁺, Ce³⁺rareearth ions doped Ca₃Si₂O₇samples were analyzed and discussed; besides, detailed studies werecarried out on the correlation between Ca₃Si₂O₇crystal structure and the luminescent properties ofEu²⁺ion. With Eu²⁺and Ce³⁺co-doping in Ca₃Si₂O₇crystal lattice, Ce³⁺-Eu²⁺energy transfer occurs,accompanying with the sensitized luminescence of Ce³⁺and the improvement of Eu²⁺luminescenceefficiency. The research work mainly focused on the following aspects:（1） During the preparation process of Ca₃Si₂O₇, an optimal content of H₃BO₃flux couldsuccessfully suppress the formation of impurity phase, and thus enhancing the luminescent propertiesof rare-earth-doped Ca₃Si₂O₇phosphors.（2） The correlation between crystal structure and luminescent properties was investigatedsystematically. Because of the strong crystal field caused by the distortion in Eu²⁺doped Ca₃Si₂O₇crystal lattice, a wide band excitation spectrum is expected to occur, which covers from near-UV tothe blue light region, implying a good match with near-UV or blue LED chips. The emission spectrumis located at603nm within the red region, with FWHM of110nm, which benefits the realization ofwarm white LEDs with high color rendering properties. Also, the single symmetry of the emissionspectra reveals the similarity of oxygen coordination for three kinds of Ca2+ions in Ca₃Si₂O₇crystalstructure.（3） The luminescent properties of Ce³⁺doped Ca₃Si₂O₇samples were investigated. The excitationspectrum of Ca₃Si₂O₇: Ce³⁺, Li+is located at300-350nm in the near-ultraviolet region. The emissionspectrum covers350-500nm from the near-ultraviolet to the blue region, with a large overlap with theexcitation spectrum of Eu²⁺doped Ca₃Si₂O₇, which makes the energy transfer between Ce2+and Eu²⁺possible. （4） The mechanism of energy transfer between Ce2+and Eu²⁺in the Eu²⁺and Ce³⁺co-dopedCa₃Si₂O₇samples was explored. The energy transfer between Ce2+and Eu²⁺further improves theluminescent intensity of Eu²⁺, leading to a high energy conversion efficiency up to93%. Themechanism of energy transfer is deduced to be the electric dipole-dipole interaction, with a criticaltransfer distance of26.79.