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Abstract: M4.95−y (PO4)3Cl:0.05Eu2+, yMn2+ (M=Ca, Sr) phosphors were synthesized at 1200°C under a reductive atmosphere. The energy transfer mechanism and efficiency (η) from Eu2+ to Mn2+ as well as the quantum efficiency (Q) of the Mn2+ emission were analyzed using PL spectra and decay curves. Least squares fittings of the Eu2+ decay curves indicate that the energy transfer from Eu2+ to Mn2+ follows the exchange mechanism in the Sr system, while besides exchange mechanism other complicated quenching processes are involved in the Ca system. Superficially the η is high but the Q is low, which implies some energy loss. Two quenching models representative of an “inverse bottleneck process”, which is related to the lifetime mismatch between Eu2+ and Mn2+, and a “charge transfer process“ in the Eu2+–Mn2+ clusters, are proposed. The results may provide some clues for designing excellent sensitizer and activator co-doped phosphors in our further work. [Copyright &y& Elsevier]

A series of tunable blue-green emitting phosphors Al 5 O 6 N: Eu2+, Tb3+ were prepared via gas-pressure sintering reaction process. The morphology, UV–Vis reflectance spectra, photoluminescence properties, decay behavior, Eu2+ occupy site, energy transfer mechanism and thermal stability were investigated systematically. The Al 5 O 6 N: 0.003Eu2+, 0.01Tb3+ phosphor exhibits strong green emission under near-UV excitation due to briskly efficient energy transfer from Eu2+ to Tb3+. The maximum energy transfer efficiency calculated by decay lifetime can reach 80%. The mechanism of energy transfer from the Eu2+ to Tb3+ is considered to be a dipole−dipole type. The critical distance of the energy transfer is calculated via the concentration quenching method. Moreover, the color emission from blue to green can be obtained through controlling the concentration of Eu2+ and Tb3+. These results reveal the potential value of Al 5 O 6 N: Eu2+, Tb3+ phosphors as green light emitting material for near-UV pumped white light-emitting diodes. [ABSTRACT FROM AUTHOR]

Due to Eu2+ and Eu3+ ions often co-exist in the crystal lattices, the luminous intensity of some phosphors is limited greatly. In this work, we propose a crystal-site engineering approach to reduce Eu3+ to Eu2+ in the KBaYSi 2 O 7 lattice through substitution of Ba2+ by Ca2+ or Sr2+. The mechanism between the local environmental regulation of the crystal structure around Eu2+ as well as the luminous intensity and thermal stability of the phosphor was systematically explored. The results of XRD, Rietveld refinement and EDX confirmed that Ca2+ and Sr2+ are dissolved into the crystal lattice effectively without changing the main phase structure. As a result, the luminous intensity of samples doped Ca2+ and Sr2+ increased by 39.7% and 41.2%, respectively. The mechanisms for such improvement is ascribed to the reduction of Eu3+ into Eu2+ under the lager volume of [EuO 9 ] 2 polyhedron. The treated samples exhibited relatively superior thermal stability with I 150°C > 70%, indicating that doping with Ca2+ or Sr2+ have no effect on the thermal stability. A pc-WLED device fabricated by combining (Ba,Sr) 2 SiO 4 :Eu2+, (Ca,Sr)AlSiN 3 :Eu2+, BaSi 2 O 2 N 2 :Eu2+ and KBa 0.86 Ca 0.1 YSi 2 O 7 :Eu2+ with 380 nm chip exhibits CCT (5010 K) and high CRI (96.6). These results indicate that this phosphor has potential for applications in full-spectrum warm white lighting. • The luminous intensity of KBa 0.96 YSi 2 O 7 :Eu2+ doped Ca2+ and Sr2+ increased by 39.7% and 41.2%, respectively. • The effective concentration of Eu2+ ions was enhanced by structural modulation. • A white-LED device with an excellent CRI (Ra = 96.6) and low CCT (5010 K) was obtained. [ABSTRACT FROM AUTHOR]