Preparation, structural and optical characteristics of a deep red-emitting Mg2Al4Si5O18: Mn4+ phosphor for warm w-LEDs

- Red phosphors Mg2Al4Si5O18:Mn4+ were synthesized for the first time.
- This phosphor can be efficiently excited by near-UV/blue light to emit deep red emission.
- Temperature dependence spectrums are investigated to demonstrate its good thermal stability.
- The fabrication of red-emitting LED revealed its potential application in WLEDs.

A novel red-emitting phosphor Mg2Al4Si5O18:Mn4+ is successfully synthesized using a solid-state reaction method. Aluminosilicate Mg2Al4Si5O18 of low-symmetry orthorhombic phase contains abundant octahedrons and is suitable for Mn4+ doping. A broad absorption band ranging from 240 nm to 550 nm in the ultraviolet-visible spectra corresponds to the photoluminescence excitation spectrum. The emission spectrum from 650 nm to 750 nm exhibits a strong emission peak at 680 nm because of the 2Eg→4A2g transition of Mn4+ ion. The critical distance Rc for concentration quenching is ∼33.3 Å, and the energy transfer mechanism is determined to be dipole-dipole interaction. Luminescence mechanism is analyzed using the energy level diagram of Mn4+ ion. Racha parameters B and C are evaluated and used to discuss the nephelauxetic effect for the Mn4+ ions in the Mg2Al4Si5O18. Temperature-dependent fluorescence test demonstrates the good thermal optical properties of the phosphor. An assembled light-emitting diode (LED) device with efficient luminescence demonstrates its practical use. Results indicate the potential application of the phosphor for white LEDs.

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