Red phosphors play an indispensable role in phosphor-based warm white light emitting diodes (WLEDs). We demonstrated recently that the non-rare-earth phosphor Sr 4 Al 14 O 25 :Mn 4+ exhibits red luminescence even more intensely than the commercial Mn 4+ phosphor 3.5MgO.0.5MgF 2 .GeO 2 :Mn 4+ upon blue excitation. Herein, on the basis of crystal field calculations employing the exchange charge model, we identify the energy levels of three types of Mn 4+ ions situated at Al 3+ sites in the Sr 4 Al 14 O 25 crystal lattice and find that the doped manganese ions occupy preferentially the Al4 and Al5 more highly covalent sites rather than the Al6 site. We report that the Mn 4+ luminescence can be enhanced upon the inclusion of Mg 2+ in the synthesis reaction.The mechanisms for this effect comprise the lower nonradiative decay rate from the 2 E g state due to the reduction in energy migration along Mn 4+ ions to killer sites and also the morphology evolution from orderly layered smooth nanosheets to irregular nanoparticles disorderly compacted in porous bundles. Interestingly, various other phases are formed upon the addition of Mg 2+ . The resistance of Mn 4+ photoluminescence in the phosphor to thermal impact has also been studied and no obvious thermal degradation after a cycle experiment by heating and cooling the sample between 25 o C and 300 o C was found. As proof of concept, a warm perception WLED has been made when the phosphor was applied to the package of a blue LED chip and YAG:Ce.

Searching for an efficient non rare earth‐based oxide red phosphor, particularly excitable by light in the wavelength from 380 to 480 nm and unexcitable by green light, is essential for the development of warm white light emitting diodes (WLEDs). Here, we report a promising and orderly‐layered candidate: Sr4Al14O25:Mn4+ with CIE color coordinates (0.722, 0.278). It has higher luminescence efficiency particularly upon blue excitation and is much cheaper than the commercial red phosphor 3.5MgO·0.5MgF2·GeO2:Mn4+ (MMG:Mn4+). In sharp contrast to Eu2+‐doped (oxy)nitrides, the phosphor can be synthesized by a standard solid‐state reaction at 1200°C in air. The effects of flux boron content, environment, and preparation temperature, sintering dwelling time as well as Mn concentration have been systematically investigated for establishing the optimal synthesis conditions. The low temperature emission spectra reveal that there are at least three types of Mn4+ ions in Sr4Al14O25:Mn4+ due to the substitution for the distorted octahedral Al3+ sites. The AlO6 layers where Mn4+ prefers to reside are well separated from one another by AlO4 tetrahedra in one dimension parallel to axis a. This scenario can efficiently isolate Mn4+ ions from local perturbations, thereby enabling the high efficiency of luminescence. The energy transfer rates and mechanism are discussed.

Thermal luminescence quenching behavior of a phosphor is essential for application in phosphor converted white light emitting diodes (pc-WLEDs) because the phosphor layer can be heated up to 473K in a working high power WLEDs. Here, we have confirmed indeed a red luminescence of Mn(4+) substituting for calcium sites rather than tetrahedral aluminum sites in CaAl(4)O(7):Mn which can be synthesized in pure phase even with boron acid as flux, and examined the low and high temperature luminescent properties in the range of 10 to 500K. We have revealed as well as thermal quenching mechanism that distorted octahedral Mn(4+) sites suffer severe thermal quenching. This work, thus, hints a strategy to find a new Mn(4+) phosphor with better resistance to thermal impact in the future.

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