Enhancement Effect Of Photoluminescence Of Ba₃MgSi₂O₈: Eu²⁺, Mn²⁺ Phsophor For Single-chip Red/Blue Emitting LEDs

The solid-state lighting technology represented by LEDs has advantages of safety, environmental friendliness, energy-efficiency, long lifetime, small size and free maintenance. An enormous industry chain of LED based solid state lighting has been formed worldwide. The device luminous efficiency of phosphor converted LEDs, namely the external quantum efficiency of devices needs to be improved further. The luminous efficiency of LED depends on either internal quantum efficiency or light extraction efficiency of each component in a LED device. In this thesis, the fluorescence enhancement of Ba₃MgSi₂O₈:Eu²⁺,Mn²⁺ phosphors with simultaneously red-blue light emissions is investigated, in which the phosphor is pumped with GaN-based single-, near-ultraviolete chip. The energy transfer involved in Ba₃MgSi₂O₈:Eu²⁺, Mn²⁺ phosphor and its host is focused, so as to improve the luminous efficiency of single-chip red and blue LED ultimately.Three mechanisms closely relevant to this enhancement photoluminescence of Ba₃MgSi₂O₈:Eu²⁺,Mn²⁺ phosphors have been proposed as follows.A. Suppression of green-light-emitting phases in Ba₃MgSi₂O₈ host.We re-examined a coexistence of an impure phase Ba₂SiO₄ in Ba₃MgSi₂O₈, ascribed to green light emission. Similiarly, by doping Al ion to the Ba₃MgSi₂O₈ host, two coexisiting phases, Ba₂SiO₄ and BaAl2O4, have also been identified. By controlling those green-light emitting phases, it is possible to remove those impure phases to achive the fluorescence enhancement effect.B. Energy storage and its gradually released mechanism of Dy³⁺ ion added with Eu, Mn Co-doped Ba₃MgSi₂O₈It has been established that, blue light emission is origated from a typical emission of Eu²⁺ ion, and the red emission is from the 4T-6A transition of Mn²⁺ dued to the Eu²⁺- Mn²⁺ resonance energy transfer. Thus, in order to improve the effective utilization of excitation light for Eu²⁺, the Ba₃MgSi₂O₈:Eu²⁺,Mn²⁺ phophors were codoped with Dy³⁺ to promote the Dy³⁺-Eu²⁺ energy transfer, and the total quantity of Eu²⁺-Mn²⁺ transferred energy will be increased so as to achieve the fluorescence enhancement of red and blue emissions.C. Photon confinement effects of cage-like nanostructured phosphorA special morphology of phosphor in a cage-like nanostructure has been achieved via spray pyrolysis method.Compared to the fluorescence intensity of phsosphors synthesized by solid-state reaction, the fluorescence enhancement effect is maybe primarily due to the effect of scattering effects of nanosized crystallines on the external surface of microsized hollow phosphor particle and the reflection effects on internal surface of that hollow phosphor particle.The results are of values to improve quantum effiecency for either red/blue-light emitting or white-light emitting LEDs by combining Ba₃MgSi₂O₈:Eu²⁺, Mn²⁺ with GaN based chips.