Red-emitting manganese-doped aluminum nitride phosphor

Abstract

We report high efficiency luminescence with a manganese-doped aluminum nitride redemitting phosphor under 254 nm excitation, as well as its excellent lumen maintenance in fluorescent lamp conditions, making it a candidate replacement for the widely deployed europium-doped yttria red phosphor. Solid-state reaction of aluminum nitride powders with manganese metal at 1900 °C, 10 atm N 2 in a reducing environment results in nitrogen deficiency, as revealed diffuse reflectance spectra. When these powders are subsequently annealed in flowing nitrogen at 1650 °C, higher nitrogen content is recovered, resulting in white powders. Silicon was added to samples as an oxygen getter to improve emission efficiency. NEXAFS spectra and DFT calculations indicate that the Mn dopant is divalent. From DFT calculations, the UV absorption band is proposed to be due to an aluminum vacancy coupled with oxygen impurity dopants, and Mn 2+ is assumed to be closely associated with this site. In contrast with some previous reports, we find that the highest quantum efficiency with 254 nm excitation (Q.E. = 0.86±0.14) is obtained in aluminum nitride with a low manganese doping level of 0.06 mol%. The principal Mn 2+ decay of 1.25 ms is assigned to non-interacting Mn sites, while additional components in the microsecond range appear with higher Mn doping, consistent with Mn clustering and resultant exchange coupling. Slower components are present in samples with low Mn doping, as well as strong afterglow, assigned to trapping on shallow traps followed by detrapping and subsequent trapping on Mn.

Slow decay of a defect‐related emission band at 2.05 eV in AlN: Signatures of oxygen‐related DX states

“…Cherepy et al. published recently data on a 600 nm PL band in intentionally Mn doped AlN. They found a corresponding absorption at 4.88 eV and two different lifetimes (one at around ms, and the other increasing from 0.29 to 6.30 ms for decreasing Mn concentrations).…”

Unraveling the Eu2+ → Mn2+ Energy Transfer Mechanism in w-LED Phosphors

“…In displays with w-LED backlights, narrow-band red (NBR) and narrow-band green (NBG) emission widens the color gamut and allows for a higher brightness by using narrow-band emission that matches the displays’ color filter transmission. A promising candidate for narrow-band red or green emission is Mn 2+ (3d 5 ), and this ion therefore gained huge interest as an activator ion. , The d–d intraconfigurational 4 T 1 – 6 A 1 emission of Mn 2+ is typically in the green/orange spectral region for Mn 2+ in tetrahedral coordination and in the orange/red spectral region in octahedral coordination (higher crystal field strength). Unfortunately, the d–d absorption strength in the blue is extremely low, making singly doped Mn 2+ phosphors unsuitable for (In,Ga)­N-based LED excitation.…”

Increased fluorescence intensity in CaTiO3:Pr3+ phosphor due to NH3 treatment and Nb Co-doping

“…Despite intense research, alternative red phosphors for lighting applications remain a challenge. No alternative has been found to the original Y2O3:Eu phosphor developed for the first tri-color fluorescent lamp more than 40 years ago [1], though our recent efforts did identify AlN:Mn as a possible option [2]. The red phosphor is particularly demanding, because it must emit within a very narrow energy range due to a sharp decrease in eye sensitivity at longer wavelengths and a poor red color rendering index at shorter wavelengths.…”