With superior photoluminescent properties, the recently discovered A 2 MF 6 :Mn 4+ material holds the potential in replacing the commercial rare-earth-doped (oxy)nitride phosphors for solid state lighting and display. We report here a green synthetic route to synthesize narrow red emitting K 2 SiF 6 :Mn 4+ without the usage of toxic and volatile HF solution. We show that K 2 SiF 6 :Mn 4+ is produced in common low-toxic H 3 PO 4 /KHF 2 liquid instead of high-toxic HF liquid and systematically investigate its morphology and photoluminescence properties. Moreover, the reaction mechanism is comprehensively discussed in detail. We find that not only does H 3 PO 4 /KHF 2 play the same key roles as HF in the process of stabilizing Mn 4+ and promoting Mn 4+ into the host K 2 SiF 6 , but also it exhibits more excellent ability than HF in controlling the concentration of Mn 4+ ion in the host K 2 SiF 6 . By demonstrating its application in white light-emitting diode (LED) with tunable chromaticity coordinate and correlated color temperature, we show that our hydrothermal strategy based on low-toxic H 3 PO 4 /KHF 2 solution system will open the opportunity for the narrow red emitting A 2 MF 6 :Mn 4+ to be synthesized in large scale toward white LED industry adoptions.
Poor water resistance and nongreen synthesis remain great challenges for commercial narrow red-emitting phosphor AMF:Mn (A = alkali metal ion; M = Si, Ge, Ti) for solid-state lighting and display. We develop here a simple and green growth route to synthesize homogeneous red-emitting composite phosphor KSiF:Mn@KSiF (KSFM@KSF) with excellent water resistance and high efficiency without the usage of toxic and volatile hydrogen fluoride solution. After immersing into water for 6 h, the as-obtained water-resistant products maintain 76% of the original emission intensity, whereas the emission intensity of non-water-resistant ones steeply drops down to 11%. A remarkable result is that after having kept at 85% humidity and at 85 °C for 504 h (21 days), the emission intensity of the as-obtained water-resistant products is at 80-90%, from its initial value, which is 2-3 times higher than 30-40% for the non-water-resistant products. The surface deactivation-enabled growth mechanism for these phosphors was proposed and investigated in detail. We found that nontoxic HPO/HO aqueous solution promotes the releasing and decomposition of the surface [MnF] ions and the transformation of the KSFM surface to KSF, which finally contributes to the homogeneous KSFM@KSF composite structure. This composite structure strategy was also successfully used to treat KSFM phosphor prepared by other methods. We believe that the results obtained in the present paper will open the pathway for the large-scale environmentally friendly synthesis of the excellent antimoisture narrow red-emitting AMF:Mn phosphor to be used for white light-emitting diode applications.
Non-rare-earth Mn-doped double-perovskite (BaSr )YSbO:Mn red-emitting phosphors with adjustable photoluminescence are fabricated via traditional high-temperature sintering reaction. The structural evolution, variation of Mn local environment, luminescent properties, and thermal quenching are studied systematically. With elevation of Sr substituting content, the major diffraction peak moves up to a higher angle gradually. Impressively, with increasing the substitution of Ba with Sr cation from 0 to 100%, the emission band shifts to short-wavelength in a systematic way resulting from the higher transition energy from excited states to ground states. Besides, this blue-shift appearance can be illuminated adequately using the crystal field strength. The thermal quenching of the obtained solid solution is dramatically affected by the composition, with the PL intensity increasing 16% at 423 K going from x = 0 to 1.0. The w-LEDs component constructed by coupling the UV-LED chip with red/green/blue phosphors demonstrate an excellent correlated color temperature (CCT) of 3404 K, as well as color rendering index (CRI) of 86.8.
A novel red emitting fluoride phosphor, K2LiAlF6:Mn4+, with an excellent thermal quenching behavior and color stability for white LEDs is developed by a green synthetic route based on low-toxic H3PO4/KHF2liquid instead of the highly toxic HF liquid.
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