Confining Mn²⁺-Doped Lead Halide Perovskite in Zeolite‑Y as Ultrastable Orange-Red Phosphor Composites for White Light-Emitting Diodes

CsPbX₃ (X = Cl, Br, I) perovskite quantum dots (QDs) have emerged as competitive candidate luminescent materials in the photoelectric fields due to their superior luminescence properties. However, the major drawback such as poor resistance to temperature, moisture, and irradiation of light, especially for the red QDs with I^–, hinders their practical applications. Herein, we synthesized Mn²⁺-doped CsPbCl₃ embedded in the cage of zeolite-Y as a new orange-red phosphor for the white light-emitting diode (WLED). The composites have significantly improved resistance to both elevated temperature and water over the bare Mn²⁺-doped QDs. The former exhibits little degradation whereas the latter shows apparent decline upon the irradiation of lights in the orange LED devices, which are fabricated by employing each material as a color-conversion phosphor coated on a 365 nm UV chip. A WLED is also achieved with a 365 nm UV chip coated with a CsPb­(Cl_0.5,Br_0.5)₃–Y blue phosphor and a CsPb_0.75Mn_0.25Cl₃–Y orange phosphor. The device possesses a Commission Internationale de l’Éclairage coordinate of (0.34, 0.36), a correlated color temperature of 5336 K and a color rendering index of 81

Thermodynamics and Kinetics Accounting for Antithermal Quenching of Luminescence in Sc₂(MoO₄)₃: Yb/Er: Perspective beyond Negative Thermal Expansion

Defects are common in inorganic materials and not static upon annealing of the heat effect. Antithermal quenching of luminescence in phosphors may be ascribed to the migration of defects and/or ions, which has not been well-studied. Herein, we investigate the antithermal quenching mechanism of upconversion luminescence in Sc2(MoO4)3: 9%Yb1%Er with negative thermal expansion via a fresh perspective on thermodynamics and kinetics, concerning the thermally activated movement of defects and/or ions. Our results reveal a second-order phase transition taking place at ∼573 K induced by oxide-ion migration. The resulting variation of the thermodynamics and kinetics of the host lattice owing to the thermally induced oxide-ion movement contributes to a more suppressed nonradiative decay rate. The dynamic defects no longer act as quenching centers with regard to the time scale during which they stay nearby the Yb3+/Er3+ site in our proposed model. This research opens an avenue for understanding the antithermal quenching mechanism of luminescence via thermodynamics and kinetics

Highly Efficient and Thermally Stable K₃AlF₆:Mn⁴⁺ as a Red Phosphor for Ultra-High-Performance Warm White Light-Emitting Diodes

Following pioneering work, solution-processable Mn⁴⁺-activated fluoride pigments, such as A₂BF₆ (A = Na, K, Rb, Cs; A₂ = Ba, Zn; B = Si, Ge, Ti, Zr, Sn), have attracted considerable attention as highly promising red phosphors for warm white light-emitting diodes (W-LEDs). To date, these fluoride pigments have been synthesized via traditional chemical routes with HF solution. However, in addition to the possible dangers of hypertoxic HF, the uncontrolled precipitation of fluorides and the extensive processing steps produce large morphological variations, resulting in a wide variation in the LED performance of the resulting devices, which hampers their prospects for practical applications. Here, we demonstrate a prototype W-LED with K₃AlF₆:Mn⁴⁺ as the red light component via an efficient and water-processable cation-exchange green route. The prototype already shows an efficient luminous efficacy (LE) beyond 190 lm/W, along with an excellent color rendering index (Ra = 84) and a lower correlated color temperature (CCT = 3665 K). We find that the Mn⁴⁺ ions at the distorted octahedral sites in K₃AlF₆:Mn⁴⁺ can produce a high photoluminescence thermal and color stability, and higher quantum efficiency (QE) (internal QE (IQE) of 88% and external QE (EQE) of 50.6%.) that are in turn responsible for the realization of a high LE by the warm W-LEDs. Our findings indicate that the water-processed K₃AlF₆ may be a highly suitable candidate for fabricating high-performance warm W-LEDs

Highly Efficient and Stable Narrow-Band Red Phosphor Cs₂SiF₆:Mn⁴⁺ for High-Power Warm White LED Applications

Due to the unique narrow-band red emission and broadband blue light excitation, as well as milder synthesis conditions, Mn⁴⁺ ion activated fluoride red phosphors show great promise for white light emitting diode (W-LED) applications. However, as the Mn⁴⁺ emission belongs to a spin-forbidden transition (²E_g → ⁴A₂), it is a fundamental challenge to synthesize these phosphors with a high external quantum efficiency (EQE) above 60%. Herein, a highly efficient and thermally stable red fluoride phosphor, Cs₂SiF₆:Mn⁴⁺, with a high internal quantum efficiency (IQE) of 89% and ultrahigh EQE of 71% is demonstrated. Furthermore, nearly 95% of the room-temperature IQE and EQE are maintained at 150 °C. The static and dynamic spectral measurements, as well as density functional theory (DFT) calculations, show that the excellent performance of Cs₂SiF₆:Mn⁴⁺ is due to the Mn⁴⁺ ions being evenly distributed in the host lattice Cs₂SiF₆. By employing Cs₂SiF₆:Mn⁴⁺ as a red light component, stable 10 W high-power warm W-LEDs with a luminous efficiency of ∼110 lm/W could be obtained. These findings indicate that red phosphor Cs₂SiF₆:Mn⁴⁺ may be a highly suitable candidate for fabricating high-performance high-power warm white LEDs