RESUMO
Wide-spectrum displays require narrow-band red phosphors activated by Mn4+, but most of them, such as K2SiF6:Mn4+, have long fluorescence decay lifetimes (>7 ms) that hinder their use in fast-response backlights. Interestingly, K2LiAlF6:0.05Mn4+ has a shorter fluorescence lifetime (3.43 ms), but its disadvantage is that its luminescence intensity is relatively weak. So, in this study, the luminescence intensity of K2LiAlF6:0.05Mn4+ is improved by doping with Zn2+. The experimental results show that enhancement of the luminous intensity is as high as 39%, the fluorescence lifetime is only increased by 13% (3.89 ms), and it is still less than 4 ms. Through experiments and differential charge density calculations, it has been revealed that the luminescence intensity improvement is due to an increased crystalline quality during the synthesis process. Specifically, the co-doping of Zn2+ reduces the formation of impurity ions Mn2+ and Mn3+ and the generation of K+ vacancies caused by nonequivalent doping. We demonstrate the advantage of this phosphor over K2SiF6:Mn4+ in terms of response speed by using a camera. It emits only weak red light after the blue chip stops working for 5 ms, indicating its potential application in next-generation fast-response displays.
RESUMO
Although Mn4+-activated fluoride phosphors have high luminescence quality, their poor water resistance and thermal fluorescence properties significantly limit their practical applications. Here, we propose a surfactant modification strategy by adding the surfactant cetyltrimethylammonium bromide (CTAB) to the synthesis and modifying the surface of the phosphor with ethylene diamine tetraacetic acid (EDTA) to obtain a phosphor with excellent luminescence thermal properties and water resistance, K2TiF6:Mn4+-xCTAB-EDTA (KTFM-xC-E) phosphors. The experimental and X-ray diffraction Rietveld refinement results confirm that the phosphor has higher structural rigidity and thus improved thermal stability. The surface modification with EDTA resulted in the formation of a dilute Mn4+ shell layer on the phosphor surface, which prevented the inward hydrolysis of the phosphor and resulted in excellent water resistance. Therefore, we have successfully modified K2TiF6:Mn4+ (KTFM) phosphors using low-cost surfactants, which also provides new ideas for other commercial high-quality phosphors.
RESUMO
In situ synthesis of cyano-bridged Cu (I)/Cu (II) complexes usually requires organometallic catalysts or is carried out under high-temperature and high-pressure conditions. Herein, the cyano-bridged two-dimensional Cu (I)/Cu (II) photocatalyst, [Cu2 (Py)3(CN)3]n (1), is synthesized in situ at room temperature. The in situ synthesis mechanism of 1 shows that the partial Cu (II) complex catalyzed the C-C bond cleavage of 1,3-isophthalonitrile (L) to introduce -CN and generate Cu (I)/Cu (II). Its ultrathin nanosheets can be obtained by adding sodium dodecyl benzene sulfonate and performing ultrasonic synthesis in the process of synthesis 1. The ultrathin nanosheets of 1 have a lattice distance of about 0.31 nm, and it can rapidly decompose methylene blue (MB) (K = 0.25 mg L-1 min-1 at pH = 3). This research work is beneficial for in situ synthesis of cyano-bridged Cu (I)/Cu (II) complexes at room temperature and explores their synthesis and photocatalytic mechanism.
RESUMO
A new type of monoethanolamine (MEA) and Mn4+ co-doped KTF : MEAH+, Mn4+ (K2TiF6 : 0.1MEAH+, 0.06Mn4+) red emitting phosphor was synthesized by an ion exchange method. The prepared Mn4+ co-doped organic-inorganic hybrid red phosphor exhibits sharp red emission at 632 nm and the emission intensity at room temperature is 1.43 times that of a non-hybrid control sample KTF : Mn4+ (K2TiF6 : 0.06Mn4+). It exhibits good luminescent thermal stability at high temperatures, and the maximum integrated PL intensity at 150 °C is 2.34 times that of the initial value at 30 °C. By coating a mixture of KTF : MEAH+, Mn4+, a yellow phosphor (YAG : Ce3+) and epoxy resin on a blue InGaN chip, a prototype WLED (white light-emitting diode) with CCT = 3740 K and R a = 90.7 is assembled. The good performance of the WLED shows that KTF : MEAH+, Mn4+ can provide a new choice for the synthesis of new Mn4+ doped fluoride phosphors.
RESUMO
Mn4+-doped fluoride phosphors are efficient narrowband red-emitting phosphors for white light-emitting diodes (WLEDs) and backlight displays. However, erosion by moisture is the main obstacle that limits their application. In this work, LNSF:Mn4+ (Li0.06Na1.94Si0.94Mn0.06F6) with high quantum yield (QY), luminescent thermal stability, and waterproofness was synthesized using the H2O2-free reaction method at room temperature. Compared to NSF:Mn4+(Na2Mn0.06Si0.94F6), the QY value, luminescence thermal stability, and water resistance of LNSF:Mn4+ are obviously improved by codoping of Li+ because of the formation of charge-carrier transfer (CT) and rare-Mn4+ layer induced by codoping of Li+. The former produces the negative thermal quenching (NTQ) effect, which results in the improvement of the luminescent thermal stability. The latter can inhibit the hydrolysis of Mn4+ on the surface of the sample, which leads to the enhancement of waterproofness. The formation mechanism of the rare-Mn4+ layer is discussed. A prototype WLED emitting the ideal warm white light (CCT = 3173 K, Ra = 90.4) was assembled by coating a mixture of LNSF:Mn4+, yellow emitting phosphor (YAG:Ce3+), and epoxy resin on the blue light InGaN chip, indicating that the performance of the WLED can be improved by using LNSF:Mn4+.
