Enriching the Deep-Red Emission in (Mg, Ba)₃M₂GeO₈: Mn⁴⁺ (M = Al, Ga) Compositions for Light-Emitting Diodes

Abstract

Red emission from Mn4+-containing oxides inspired the development of high color rendering and cost-effective white-light-emitting diodes (WLEDs). Aiming at this fact, a series of new crystallographic site modified (Mg, Ba)3M2GeO8: Mn4+ (M = Al, Ga) compositions were developed with strong deep-red emission in the reaction to UV and blue lights. The Mg3Al2GeO8 host is composed of three phases: orthorhombic-Mg3Ga2GeO8, orthorhombic-Mg2GeO4, and cubic-MgAl2O4. However, Mg3Ga2GeO8 secured an orthorhombic crystal structure. Interestingly, Mg3Al2GeO8: Mn4+ showed a 13-fold more intense emission than Mg3Ga2GeO8: Mn4+ since Mn4+ occupancy was preferable to [AlO6] sites compared to [GaO6]. The coexisting phases of MgAl2O4 and Mg2GeO4 in Mg3Al2GeO8: Mn4+ contributed to Mn4+ luminescence by providing additional [AlO6] and [MgO6] octahedrons for Mn4+ occupancy. Further, these sites reduced the natural reduction probability of Mn4+ to Mn2+ in [AlO4] tetrahedrons, which was confirmed using cathodoluminescence analysis for the first time. A cationic substitution strategy was employed on Mg3M2GeO8: Mn4+ to improve the luminescence, and Mg3–x Ba x M2GeO8: Mn4+ (M = Al, Ga) phosphors were synthesized. Partial substitution of larger Ba2+ ions in Mg2+ sites caused structural distortions and generated a new Ba impurity phase, which improved the photoluminescence. Compositionally tuned Mg2.73Ba0.27Al1.993GeO8: 0.005Mn4+ exhibited a 35-fold higher emission than that of Mg3Ga1.993GeO8: 0.005Mn4+. Additionally, this could retain 70% of its ambient emission intensity at 453 K. A warm WLED with a correlated color temperature (CCT) of 3730 K and a CRI of 89 was fabricated by combining the optimized red component with Y3Al5O12: Ce3+ and 410 nm blue LED. By tuning the ratio of blue (BaMgAl10O17: Eu2+), green (Ce0.63Tb0.37MgAl11O19), and red (Mg2.73Ba0.27Al2GeO8: 0.005Mn4+) phosphors, another WLED was developed using a 280 nm UV-LED chip. This showed natural white emission with a CRI of 79 and a CCT of 5306 K. Meanwhile, three red LEDs were also fabricated using the Mg2.73Ba0.27Al1.993GeO8: 0.005Mn4+ phosphor with commercial sources. These could be potential pc-LEDs for plant growth applications.

Ultra-bright and thermally stable deep red emitting doped yttrium zirconate nanoparticles for tunable white LEDs and indoor plant growth

“…Particularly, the 5 D 0 – 7 F 4 peak located at 700 nm overlapped with the intense P FR peak, which was crucial in stimulating seed propagation and plant growth. 51–53 Hence, as a smart approach, the deep red emission of the developed optimized red emitting phosphor can be utilized to fabricate deep red pc-LEDs for use as a promising artificial light source for cultivating indoor plants. 52,53…”

“…51–53 Hence, as a smart approach, the deep red emission of the developed optimized red emitting phosphor can be utilized to fabricate deep red pc-LEDs for use as a promising artificial light source for cultivating indoor plants. 52,53…”

High-efficiency energy transfer in the strong orange-red-emitting phosphor CeO2:Sm3+, Eu3+

“…1–3 A popular method for manufacturing WLEDs is combining tricolor phosphor powder (blue, green, and red phosphors) with an ultraviolet (UV) InGaN chip. 4,5 However, these WLEDs present a high correlated color temperature and low color rendering index due to the lack of a red component. 6,7 To overcome these drawbacks, scholars should explore new red phosphors for WLED applications.…”

Highly efficient blue‐emitting phosphor via charge compensation strategy and its application for white LED lighting

“…These problems can be solved by using the near‐ultraviolet (n‐UV) light pumped WLEDs consisting of red, green, and blue phosphors 13–16 . In this scheme, high‐efficiency phosphors with appropriate excitation and emission spectra are obviously the key components for high‐quality WLEDs 12,17–20 …”

“…[13][14][15][16] In this scheme, high-efficiency phosphors with appropriate excitation and emission spectra are obviously the key components for high-quality WLEDs. 12,[17][18][19][20] The activators and host materials are crucial for conceiving appropriate phosphor. [21][22][23][24] Among the lanthanides, Ce is often used as activators for obtaining broader emission band phosphors because of the parity allowed 4f−5d electric dipole transition.…”