Competitive Site Occupation toward Improved Quantum Efficiency of SrLaScO₄:Eu Red Phosphors for Warm White LEDs

Abstract

Currently, the typical WLEDs are manufactured by combining blue GaInN LED chips with green/yellow phosphors. However, this type of WLED device shows a poor color-rendering index (R a < 75) and high correlated color temperatures (CCT > 4500 K) due to the absence of the red components in the output spectrum. [2] Up to now, many types of redemitting phosphors have been reported, such as CaAlSiN 3 :Eu 2+ , Sr[LiAl 3 N 4 ]:Eu 2+ , K 2 SiF 6 :Mn 4+ , and so on. [3] Although nitride phosphors present high photoluminescence quantum yield (PLQY) and excellent thermal stability, the expensive reagents and harsh synthesis conditions of high temperature and high pressure push up the cost for daily uses. Meanwhile, Mn 4+ -doped fluoride phosphors also show some drawbacks, such as low chemical stability and the unavoidable usage of corrosive anhydrous HF. Therefore, it is of vital importance to explore novel blue-light-excitable red-emitting phosphor with high PLQY, excellent thermal stability, and low cost in the oxide-based material systems. The discovery of Eu2+ -doped high-efficiency red phosphors remains a vital challenge for white light-emitting diode (WLED) applications. It is therefore urgent to find effective strategies managing the oxidation state to help reduce Eu 3+ to Eu 2+ and accordingly increase the photoluminescence quantum yield (PLQY). Herein, a new red-emitting SrLaScO 4 :Eu phosphor is designed, and the PLQY is enhanced from 13% to 67% under 450 nm excitation by employing (NH 4 ) 2 SO 4 -assisted sintering. Combined structural analysis, optical spectroscopy, and theoretical calculation reveal that predominant Eu 2+ prefers to occupy the Sr 2+ sites in the SrLaScO 4 enabling red emission, and a competitive site occupation of Eu 3+ in La 3+ can be restrained, and the reduction mechanism of Eu 3+ to Eu 2+ originating from the (NH 4 ) 2 SO 4 addition is analyzed. The fabricated WLED device using red-emitting SrLaScO 4 :Eu and yellow-emitting Y 3 (Al,Ga) 5 O 12 :Ce 3+ exhibits a high color-rendering index of 86.7 at a low correlated color temperature of 4005 K. This work provides a feasible reduction strategy for guiding the development of high-efficiency Eu 2+ -doped red phosphor for WLED applications.

A new class of battery-free, mechanically powered, piezoelectric Ca5Ga6O14:Tb3+ phosphors with self-recoverable luminescence

“…The ratio of the integrated intensity of the two emission bands, called the asymmetry parameter R :is calculated to be 4.5, confirming that the crystallographic site largely deviates from inversion-symmetry. 32,33 This agrees well with the fact that the lattice possesses the non-centrosymmetric mm2 point group.…”

“…is calculated to be 4.5, confirming that the crystallographic site largely deviates from inversion-symmetry. 32,33 This agrees well with The polar mm2 point group potentially enables the orthorhombic Ca 5 Ga 6 O 14 to be piezoelectric with giant piezoelectric coefficients. The piezoelectric effect is an electromechanical coupling effect, which can be described by piezoelectric stress tensors e ijk and the strain tensors d ijk , and they can be obtained as the sum of ionic and electronic contributions: 34,35 e ijk ¼ @P i @e jk ¼ e elc ijk þ e ion ijk (4) and…”

Governing the crystallographic sites for tuning Eu2+ emission in an apatite oxyfluoride host to be applied for superior white light emitting diodes

“…As compared with the XRD refinement data of CSLOF:0.04Eu 2+ , the cell volume enhancement from 582.65 [Å 3 ] to 590.42 [Å 3 ] for CSLOF:0.04Eu 2+ ,1.2Ba 2+ might be caused by the replacement of Ba 2+ ions with Eu 2+ ions. 44 When less electronegative and larger Ba 2+ ions are introduced to the cationic sites of CSLOF:0.04Eu 2+ , it causes an enhancement in the lattice size and also increases the centroid shift ( ε c ) of the 5d orbital of the Eu 2+ ions. This reduces the energy gap in the 5d–4f electronic transition of Eu 2+ ions and results in a higher wavelength emission.…”

Light-Induced Charge Transfer to Achieve Deep-Red Emission in SrSc2O4:Bi toward Multiple Optical Applications

“…CsPbI 3 QDs display highly efficient narrow-band red emission, but Pb toxicity and poor stability limit their practical applications. , For Mn 4+ -activated fluoride materials, the long photoluminescence decay lifetime (on the order of millisecond) is undesirable for lighting and displays. Eu 2+ -activated inorganic luminescent materials can emit red and even near-infrared (NIR) light when the dopant ion is subjected to a large crystal-field influence, like that in nitrides or in a small lattice of oxides. − The incorporation of Eu 2+ into strong-crystal-field hosts has been developed into an effective strategy to achieve red and NIR light. , Nevertheless, Eu 2+ -doped luminescent materials are often prepared under reducing conditions that require expensive and sophisticated equipment.…”

“…11− 15 The incorporation of Eu 2+ into strong-crystal-field hosts has been developed into an effective strategy to achieve red and NIR light. 16,17 Nevertheless, Eu 2+ -doped luminescent materials are often prepared under reducing conditions that require expensive and sophisticated equipment.…”