Improvement of emission intensity, colour rendering index and thermal stability of Ca9Ce(PO4)7:Eu2+,Mn2+via H3BO3 doping

Abstract

Ca_8.78Ce (PO₄)₇:0.06Eu²⁺,0.16Mn²⁺,xH₃BO₃ phosphors were synthesized by a high-temperature solid-state reaction method. XRD patterns of the samples indicate that H₃BO₃ doping does not change the phase formation. However, H₃BO₃ doping can change the emission intensities of Ce³⁺, Eu²⁺, Mn²⁺ and the energy transfer efficiencies of Ce³⁺–Eu²⁺ and Ce³⁺–Mn²⁺. The reason for this is that H₃BO₃ doping changes the luminescent centre and the distance between different luminescent centres to some degree. When the ligand polyhedron volume decreases, the lifetime and emission intensity of the luminescent centre will increase. When the distance between Ce³⁺ and Eu²⁺/Mn²⁺ decreases, the energy transfer efficiency between them will increase. In Ca_8.78Ce(PO₄)₇:0.06Eu²⁺,0.16Mn²⁺,xH₃BO₃, the average volume of an [(Eu/Mn)1/2/3–O_8/9] polyhedron will decrease from 27.511 ų to 21.847 ų, and the average distance between Ce and (Eu/Mn)1/2 will decrease from 3.702 Å to 3.573 Å with increased doping amounts of H₃BO₃ from 0 to 7. Meanwhile, the emission intensity and lifetime of Ce³⁺ decrease, and those of Eu²⁺/Mn²⁺ increase. Furthermore, the energy transfer efficiency from Ce³⁺ to Eu²⁺/Mn²⁺ and the quantum efficiency are improved. H₃BO₃ doping improves the ratio of red, green and blue colours of the spectrum, which improves the colour rendering index of materials from 80.5 to 90.7. H₃BO₃ doping also improves the thermal stability of the material to some degree. The quenching temperature of Eu²⁺ is improved from 75 °C to 100 °C.