Improved Blue‐Emitting AlN:Eu²⁺ Phosphors by Alloying with GaN

Abstract

A method is designed to improve the luminescence of AlN-based phosphors by tuning the band structure and crystal structure due to alloying with GaN. The pure (Al,Ga)N:Eu phosphors were initially prepared by gas-phase reaction in an NH 3 atmosphere. GaN alloying was used to expand the crystal lattice of AlN due to Ga 3+ substituting for smaller Al 3+ ions, making dissolution of Eu 2+ easier. The dissolution of Ga in the AlN lattice was proven by the result of the Rietveld refinement and the increase in lattice parameters with increasing Ga content. To introduce other energy states mixing with the 5d states of Eu 2+ , Ga doping was also used to tune the band structure of AlN by acting on Eu 2+ ions. The theoretical result was analyzed using the Cambridge Sequential Total Energy Package (CASTEP). According to the calculated total and atom resolved partial density of states, it was observed that the Ga 5p states contribute a large portion to the corresponding Eu 2+ absorption band in (Al,Ga)N:Eu phosphors. As a consequence, an enhanced emission intensity at 470 nm and a high quantum efficiency for excitation at 330 nm was obtained despite of stronger thermal quenching of the (Al,Ga)N:Eu phosphors compared with AlN:Eu.

Synthesis of AlN: Eu2+ green phosphors by a simple direct nitridation method

“…When the temperature is >1133 K (> 760°C), the Gibbs' free energy of the reaction becomes negative, thus reduction of Eu(III) to Eu(II) is feasible thermodynamically. The reductive effect of ammonia was also reported by Yin et al; in their study, loss of the Ga element was ascribed to the reductive product Ga 2 O gas. Minor alumina was present in the nitridated product, thus the Eu(II) oxide reacted with alumina to form Eu‐aluminates: EuO + Al 2 O 3 = EuAl 2 O 4 , as confirmed by the XRD results.…”

Ca18.75Li10.5[Al39N55]:Eu2+—Supertetrahedron Phosphor for Solid-State Lighting

“…A negative influence of the AlN side phase on the thermal behavior of the emission seems unlikely, since AlN itself is optically inactive. Eu 2+ -doped samples of AlN show blue luminescence only in conjunction with either codoping by Si (<9%) or partial substitution of Al by Ga . Here, AlN is merely an additional scattering material.…”

“…A negative influence of the AlN side phase on the thermal behavior of the emission seems unlikely, since AlN itself is optically inactive. Eu 2+ -doped samples of AlN show blue luminescence only in conjunction with either codoping by Si (<9%) 36 or partial substitution of Al by Ga. 37 Here, AlN is merely an additional scattering material. Still, a hypothetical nonradiative energy transfer from Ca 18.75 Li 10.5 [Al 39 N 55 ]:Eu 2+ to AlN:Eu 2+ and subsequent dissipation cannot be totally excluded.…”

Lanthanide-Activated Phosphors Based on 4f-5d Optical Transitions: Theoretical and Experimental Aspects

“…This condition leads to designable chemical reduction of Eu 3+ to Eu 2+ or prevents the oxidation of Ce 3+ . The final products thus have the ability to emit tunable luminescence from blue to red depending on the nature of the host lattices. − …”