Spectroscopic investigation of La7Ta3W4O30:Sm3+ orange-red phosphor for white LEDs

The novel orange-red light emitting La₇Ta₃W₄O₃₀:xSm³⁺ (x = 0.005–0.20) phosphors were synthesized via the solid-state reaction method. The crystal structure, photoluminescence (PL) properties, optimum concentration, color purity, decay life, and thermal stability of the samples were systematically studied. Under the excitation of 404 nm, La₇Ta₃W₄O₃₀:Sm³⁺ emits intense orange-red light at 597 nm. The PL spectra of La₇Ta₃W₄O₃₀:Sm³⁺ phosphors are ascribed to the ⁴G_5/2 to ⁶H_J (J = 5/2, 7/2, 9/2, and 11/2) transitions of Sm³⁺ ions. The concentration quenching occurs at the doping level of 1 mol%. The quenching temperature is higher than 500 K. Finally, a white LED (w-LED) with the Commission Internationale de L'Eclairage (CIE) chromaticity coordinates of (0.312, 0.296) and good color rendering index (Ra) of 86 was fabricated. As a consequence, all the results suggest that the orange-red phosphors La₇Ta₃W₄O₃₀:Sm³⁺ have potential applications in w-LEDs structures.     

A red-emitting Ca8MgLa(PO4)7:Ce3+,Mn2+ phosphor for UV-based white LEDs application

Ca(8)MgLa(PO(4))(7):Ce(3+),Mn(2+) phosphors have been prepared by a conventional solid state reaction under a weak reductive atmosphere. The crystal structure and photoluminescent properties were investigated. It was found that the red emission at 640nm originated from the (4)T(1)((4)G)→(6)A(1)((6)S) transition of Mn(2+) increases dramatically by a factor of 6.4 with the optimum Ce(3+) co-doping. The energy transfer from Ce(3+) to Mn(2+) was proposed to be resonance-type via an electric dipole-dipole mechanism and the energy transfer efficiency was also calculated by the relative emission intensity. With the broadband ultraviolet (UV) absorption of Ce(3+) and the suitable color coordinates, Ca(8)MgLa(PO(4))(7):Ce(3+),Mn(2+) phosphors might be a promising candidate as red phosphors in the field of UV-based white light-emitting diodes.     

Thermally stable deep-red emitting Sr2GdTaO6:Mn4+ double perovskites for indoor plant growth LEDs

Indoor artificial cultivation of plants is a novel technology applied to agriculture, and the emission band of luminescent materials can be matched with the needs of plants to promote plant growth. In this contribution, novel Mn⁴⁺ doped Sr₂GdTaO₆ (SGTO) deep-red phosphor was synthesized. This material was characterized, in detail, by X-ray diffractometer, SEM, and photoluminescence emission spectra. Sr₂GdTaO₆:Mn⁴⁺ (SGTO:Mn⁴⁺) can be effectively excited by near-ultraviolet (NUV) light, and the broadband emission of deep-red light matches the absorption band of plant phytochromes P_R and P_FR. The optimum doping concentration of Mn⁴⁺ in SGTO was 0.6 mol%, and the concentration quenching mechanism was attributed to dipole-quadrupole (d-q) electric interaction. The photoluminescence emission intensity of SGTO:0.006Mn⁴⁺ at 423 K is 80.6% of that at room temperature and the internal quantum efficiency of SGTO:0.006Mn⁴⁺ is 36.09%. Finally, the performance of the commercial 440 nm light-emitting diode chip/SGTO:0.006Mn⁴⁺ encapsulated light-emitting diode device was stable and can meet the needs of plants for the blue and red light. The results showed that SGTO:0.006Mn⁴⁺ deep-red phosphor is expected to be a phosphor suitable for indoor plant growth lighting.     

Novel high-saturated red-emitting phosphor Sr9(Mg0.5Mn0.5)K(PO4)7: Eu2+ with great quantum efficiency enhancement by La3+ codoping for white LED application

In this work, a novel whitlockite-structure red-emitting phosphor host, Sr₉(Mg_0.5Mn_0.5)K(PO₄)₇, is designed and successfully synthesized via a solid-state reaction. Upon X-ray diffractometer Rietveld refinement, it is revealed that this compound possesses compact Eu²⁺-Mn²⁺ distance (3.6809 Å) and large intra-Mn²⁺ distance (8.9905 Å), which is beneficial to the high-efficient Eu²⁺-Mn²⁺ energy transfer. By Eu²⁺ sensitization, our new phosphor exhibits a high-saturated and bright red Mn²⁺ emission at 620 nm with high color purity of 97.9%. Great emission enhancement up to 245 times than host is achieved by La³⁺ heterovalent substitution, which can be ascribed to the La³⁺-induced further structural confinement effect. Moreover, the quantum efficiency is boosted by twofold. The as-fabricated white phosphor-converted LEDs device shows bright warm white light with correlated color temperature (CCT) of 3,487 K, color-rendering index (CRI) of 92.4, and luminous efficacy of 31.59 lm/W. This work proves the feasibility of chemical unit co-substitution strategy in emission engineering of Mn²⁺-based phosphors, which can stimulate further studies on the red-emitting phosphor materials.