Enhanced luminescence in rare-earth-free fast-sintering glass-ceramic

Abstract

One of the major challenges pursued in the luminescent materials community is to develop rare-earth-free phosphors in order to reduce the use of rare-earth elements, because of the lack of their availability and the environmental problems derived from their mining and processing. In this work, a rare-earth-free glass-ceramic-based phosphor with high photoluminescence has been designed. This novel phosphor rich in Na-rich plagioclase feldspar crystallizations presents high crystallinity, ∼94%, and a dual micro-nanostructure provided by a fast-sintering processing route. Structural disorder in Si-Al distribution favors formation of luminescent centers in the glass-ceramic material, which results in an enhancement of both the UV-blue and the red luminescence regarding natural feldspars, 1 order of magnitude and 6 times, respectively. A microstructural and structural study by means of x-ray diffraction, Raman spectroscopy, scanning electron microscopy, transmission electron microscopy (TEM), high-resolution TEM, cathodoluminescence, and nuclear magnetic resonance evidence the important role of composition in the alteration of Si-Al ordering schemes. A strong correlation between Si-Al disorder and the presence of active luminescent centers is corroborated. Our research shows a sustainable, cost-effective, innovative, and scalable material that may be considered as an alternative to rare-earth phosphors for applications such as security markers or light-emitting glasses. This novel family of rare-earth-free glass-ceramics opens a new gate through structural tailoring to enhance and tune the intrinsic luminescent emissions displayed for relevant future optical applications.

Ceramic Injection Moulding of engineered glass-ceramics: Boosting the rare-earth free photoluminescence

“…For study purposes, the sample obtained by CIM technology from the feedstock was compared to the precursor glass-ceramic, the Na-rich feldspar (albite), obtained by conventional ceramic powder process (CP), uniaxial pressed at 400kg/cm 2 and fast-sintered at 1200ºC [7][8].…”

“…Figure 7 shows the photoluminescent (PL) emission of the two studied samples when they are excited with λexc = 322nm, which corresponds to the intrinsic luminescence due to structural defects [7]. In the CIM sample, a luminescent of one order of magnitude higher than a conventional ceramic is obtained.…”

“…However, the blue luminescence is mainly produced by two kind of defects: the peaks attributed to [AlO4/alkali + ] or [AlO4] 0 defects, where Si 4+ ion is substituted by Al 3+ and the local charge balance should be maintained by a positive charge. If this positive charge is an alkali cation placed in adjacent positions to Al 3+ ions, the center formed will be [AlO4/alkali + ], while if a hole is trapped, the resulting centre will be an [AlO4] 0 [7,18,19]; and the most common structural defect in feldspars, which corresponds to Al-O --Al centers (Löwenstein bridges) (400-480 nm) which occur when an oxygen hole center is adjacent to two Al 3+ ions, one of them structural and the other one an impurity of Al [19][20][21][22][23]. The changes in the contribution of these defects can be observed by the areas ratio, which shows a trend of increasing defect population in the cases of the sample prepared from the feedstock, for [AlO4/alkali + ] or [AlO4] 0 defects.…”

“…Recently, engineered feldspars in form of glass-ceramics based on albite type structure have been obtained with interested optical properties [7,8]. These materials are free of rare-earth and possess high luminescence due to the structural defects produced by the order/disorder of its structure.…”

Improving optical properties of remote phosphor LED using green Y2O3:Ho3+ and red Mg4(F)(Ge, Sn)O6:Mn2+ layers

“…The solid-state lighting field in recent time is focusing on the semiconductor quantum dots (QDs), an innovative material that can bring about immense changes to the lighting performance of LEDs, with exceptional optical parameters, namely, the adjustable bandwidth, small emitting range and high quantum productivity [10][11][12][13]. The positive effects of QDs on the color rendering index (CRI), color gamut as well as the lighting efficacy of pc-LEDs have been verified both in theory and through practices [14][15][16]. The most frequently used packaging configurations for pc-LEDs with QDs are applying a compound of QDs and the phosphorous silicone resin or coating the QDs and the phosphor component separately.…”