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Issue 37, 2017
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Stable narrowband red phosphor K3GaF6:Mn4+ derived from hydrous K2GaF5(H2O) and K2MnF6

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A novel hydrous fluoride K2GaF5(H2O) with a special [GaF5(H2O)] group has been discovered. Interestingly, further rapidly adding K2MnF6 into the co-precipitation reaction system of K2GaF5(H2O) results in stable anhydrous cryolite phosphor K3GaF6:Mn4+. The investigation of a possible formation mechanism unravels that hydrous K2GaF5(H2O) can act as an intermediate to transform into anhydrous K3GaF6:Mn4+ induced by K2MnF6. Detailed characterizations, such as phase identification, morphology, elemental composition analysis, and IR spectra, record the time-dependent evolution process. Upon blue light excitation, phosphor K3GaF6:Mn4+ shows sharp line red emission at ∼626 nm. It presents good moisture tolerance (50% of initial luminous efficacy at 48 h), which might, due to the absence of coordinated water molecules, make the host matrix less hydrophilic. This performance, much better than those of Na3GaF6:Mn4+, K3AlF6:Mn4+, and Rb2GeF6:Mn4+, illustrates that K3GaF6 is a suitable host for Mn4+ doping. Besides, a good recovery in luminescence properties during thermal cycling (298–473 K) further demonstrates the high stability of anhydrous K3GaF6:Mn4+. By incorporating K3GaF6:Mn4+ as a red light component, a fabricated warm white light-emitting diode (WLED) presents low correlated color temperature (CCT = 3691 K), high color rendering index (Ra = 87.2 and R9 = 50.2), and a luminous efficacy of 92.1 lm W−1, and further exhibits good resistance in photoelectric properties to thermal impact with temperature ranging from 293 to 353 K, showing potential in warm WLED applications. Herein, the inductive transition from hydrous K2GaF5(H2O) to moisture-proof K3GaF6:Mn4+ is helpful for the investigation of the moisture resistance of Mn4+ activated fluorides. Moreover, these results probably propose a feasible strategy to exploit stable Mn4+-activated fluoride phosphors for warm WLED applications.

Graphical abstract: Stable narrowband red phosphor K3GaF6:Mn4+ derived from hydrous K2GaF5(H2O) and K2MnF6

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Publication details

The article was received on 12 Jul 2017, accepted on 23 Aug 2017 and first published on 24 Aug 2017

Article type: Paper
DOI: 10.1039/C7TC03116E
Citation: J. Mater. Chem. C, 2017,5, 9588-9596
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    Stable narrowband red phosphor K3GaF6:Mn4+ derived from hydrous K2GaF5(H2O) and K2MnF6

    T. T. Deng, E. H. Song, Y. Y. Zhou, L. Y. Wang, S. Ye and Q. Y. Zhang, J. Mater. Chem. C, 2017, 5, 9588
    DOI: 10.1039/C7TC03116E

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