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.

Thermal management is still a great challenge for high-power phosphor-converted white-light-emitting diodes (pc-WLEDs) intended for future general lighting. In this paper, a series of single-component white-emitting silicate SiO2-Li2O-SrO-Al2O3-K2O-P2O5: Ce(3+), Tb(3+), Mn(2+) (SLSAKP: Ce(3+), Tb(3+), Mn(2+)) glasses that simultaneously play key roles as a luminescent convertor and an encapsulating material for WLEDs were prepared via the conventional melt-quenching method, and systematically studied using their absorption spectra, transmittance spectra, photoluminescence excitation and emission spectra in the temperature range 296-498 K, decay curves, and quantum efficiency. The glasses show strong and broad absorption in 250-380 nm region and exhibit intense white emission, produced by in situ mixing of blue-violet, green, and orange-red light from Ce(3+), Tb(3+), and Mn(2+) ions, respectively, in a single glass component. The quantum efficiency of SLSAKP: 0.3%Ce(3+), 2.0%Tb(3+), 2.0%Mn(2+) glass is determined to be 19%. More importantly, this glass shows good thermal stability, exhibiting at 373 and 423 K about 84.56 and 71.02%, respectively, of the observed room temperature (298 K) emission intensity. The chromaticity shift of SLSAKP: 0.3%Ce(3+), 2.0%Tb(3+), 2.0%Mn(2+) is 2.94 × 10(-2) at 498 K, only 57% of the commercial triple-color white-emitting phosphor mixture. Additionally, this glass shows no transmittance loss at the 370 nm emission of a UV-Chip-On-Board (UV-COB) after thermal aging for 240 h, compared with the 82% transmittance loss of epoxy resin. The thermal conductivity of the glass is about 1.07 W/mK, much larger than the 0.17 W/mK of epoxy resin. An organic-resin-free WLEDs device based on SLSAKP: 0.3%Ce(3+), 2.0%Tb(3+), 2.0%Mn(2+) glass and UV-COB is successfully demonstrated. All of our results demonstrate that the presented Ce(3+)/Tb(3+)/Mn(2+) tridoped lithium-strontium-silicate glass may serve as a promising candidate for high-power WLEDs.

The design of luminescent materials with widely and continuously tunable excitation and emission is still a challenge in the field of advanced optical applications. In this paper, we reported a Eu(2+)-doped SiO2-Li2O-SrO-Al2O3-K2O-P2O5 (abbreviated as SLSAKP:Eu(2+)) silicate luminescent glass. Interestingly, it can give an intense tunable emission from cyan (474 nm) to yellowish-green (538 nm) simply by changing excitation wavelength and adjusting the concentration of Eu(2+) ions. The absorption spectra, photoluminescence excitation (PLE) and emission (PL) spectra, and decay curves reveal that there are rich and distinguishable local cation sites in SLSAKP glasses and that Eu(2+) ions show preferable site distribution at different concentrations, which offer the possibility to engineer the local site environment available for Eu(2+) ions. Luminescent glasses based color and white LED devices were successfully fabricated by combining the as-synthesized glass and a 385 nm n-UV LED or 450 nm blue LED chip, which demonstrates the potential application of the site engineering of luminescent glasses in advanced solid-state lighting in the future.

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Narrow-band green-emitting phosphor β-SiAlON:Eu has been widely used in advanced wide-gamut backlighting devices. However, the origins for unusual sharp lines in photoluminescence emission at room temperature and tunable narrow-bandemission tailored by reducing Al-O in β-SiAlON:Eu are still unclear. Here, the presence of sharp-line fine structure in the emission spectra of β-SiAlON:Eu is mainly due to purely electronic transitions (zero phonon lines) and their vibronic repetitions resulted from the multi-microenvironment around Eu 2+ ions that has been revealed by relative emission intensity of sharp line depends on excitation wavelength and monotonously increasing decay time. The specific features of the Eu 2+ occupying interstitial sites indicate that the effect of crystal field strength can be neglected. Therefore the enhanced rigidity and higher ordering structure of β-SiAlON:Eu with decreasing the substitution of Si-N by Al-O become the main factors in decreasing electron-lattice coupling and reducing inhomogeneous broadening, favouring the blue-shift and narrow of the emission band, the enhanced thermal stability, as well as the charge state of Eu 2+ . Our results provide new insights for explaining the reason for narrow-band-emission in β-SiAlON:Eu, which will deliver an impetus for the exploration of phosphors with narrow band and ordering structure.