New Insight for Luminescence Tuning Based on Interstitial sites Occupation of Eu²⁺ in Sr₃Al_2−xSi_xO_5−xN_xCl₂ (x = 0–0.4)

Abstract

Currently, the commercial fabrications of w-LEDs usually employ the strategy that combines InGaN blue chips and the Y 3 Al 5 O 12 :Ce 3+ (YAG:Ce 3+ ) yellow phosphor. [10,11] However, the well-known shortcomings are the high color temperature (CCT, > 6000 K) and low color rendering index (CRI, R a < 80), caused by the emission deficiency in the red region. [12] These shortcomings hinder the residential application of the w-LEDs in daily life. There are two common strategies to surmount this red deficiency: (1) adding the extra red emitting phosphors; [13] (2) fabricating the w-LEDs with the UV chips and the red, green, and blue phosphors. [14] However, both methods suffer from the new problems. The addition of the extra red phosphor will increase the cost, and the combination of the tri-primary phosphors to fabricate w-LEDs has the serious reabsorption issue. In order to obtain highly efficient w-LEDs with the better performance and more vivid illumination in the daily application, researchers should concentrate on developing phosphor materials that possess tunable emission with more flexibility. As one of the extensively studied activators among the lanthanide ions, Eu 2+ ions have variable photoluminescence properties due to the unique electrical configuration. [15][16][17] Eu 2+ with the electrical configuration of 4f 7 -5d exhibits less localized nature and stronger coupling to lattice vibrations. [15] Therefore, its luminescent properties are sensitive to the coordination environment such as the bond distance, symmetry, and covalence between Eu 2+ ions and ligands in the host lattice. [18] As a result, the emission of Eu 2+ could present colorful emitting colors ranged from blue to red, which makes it a perfect candidate for color tunable phosphors. [19] Currently, nitridation of phosphors provides an enormous inspiration for phosphor designing. In this paper, a nitridation process by means of substituting Al 3+ O 2− with Si 4+ N 3− in initial Sr 3 Al 2 O 5 Cl 2 :Eu 2+ system is implemented. The phase purity is confirmed by X-ray diffraction. The corresponding photoluminescence properties are recorded and analyzed by the excitation and emission spectra. Interestingly, new blue emission bands emerge in the range of 400-500 nm and the intensity increases with the increasing of substitution concentration. It is verified that the new emission band is derived from the residence of Eu 2+ ions in the interstitial sites. The crystal structure refinement, transmission electron microscopy, and solidstate nuclear magnetic resonance spectroscopy are exploited to analyze the color-tunable luminescence mechanisms induced by the structural variation. Moreover, the thermal stability is characterized by the temperature-dependent spectra. Attributed to the enhancement of lattice rigidity, the serious thermal quenching behavior is improved. Finally, the electroluminescence performance is measured for the fabricated white light-emitting diodes (LEDs). By combining 370 nm ultraviolet LED chips, CaAlSiN 3 :Eu 2+ and Sr 3 Al 2 O...

A high thermal stability Cr3+-doped gallate far red phosphor for plant lighting: structure, luminescence enhancement and application prospect

“…In previous reports, the occupation of interstitial sites often brings unexpected results. 26,27 The evolved constriction local geometric structure may affect the luminescence properties of activator Cr 3+ , which will be further discussed below.…”

Spectral properties and self-reduction of Eu3+ to Eu2+ in aluminosilicate oxyfluoride glass

“…[4][5][6][7] Impressively, due to stronger coupling to lattice vibrations (i.e., the strong interaction of 5d electrons with the local crystal eld in vicinity of Eu 2+ ), the unique electronic conguration of Eu 2+ (4f 7 -4f 6 5d) makes its luminescent properties sensitive to the coordination environment. 8,9 This is why the emission of Eu 2+ could present colorful emissions, which has recently made it a perfect candidate for color-tunable phosphors, such as the blue phosphor Mg 2 Al 4 Si 5 O 18 :Eu 2+ , 10 the green phosphor Rb 3 M(Li 3 SiO 4 ) 4 :Eu 2+ (M = Rb or Na), 11 the green-to-yellowish-orange phosphor Cs 2 MP 2 O 7 :Eu 2+ (M = Ba, Sr, and Ca), 12 the red phosphor CaS: Eu, 13 and so on. Thus, Eu 2+ doped phosphors are of great technological interest for applications in white LED, optical thermometers, backlight displays, and X-ray storage, etc.…”

Oxynitride K2Ba6.72Si16O40−1.5yNy:0.28Eu2+ phosphor with high thermal stability realized by crystal field engineering

“…7,8 Benefiting from a high covalency and a rigid structure, most (oxy)nitride phosphors exhibit excellent thermal stability. [9][10][11][12] Therefore, for alkaline earth/alkali metal based compounds, incorporating N 3− ions into oxides is not only a very important route to synthesize oxynitrides, but also can used to modify the environment surrounding the Eu 2+ ions, thus contributing to improved thermal stability and red shift. 11,12 Typical examples are, Sr 2 Al 2−x Si 1+x O 7−x N x :Eu 2+ , 13 BaMgAl 10−x Si x O 17−x N x :Eu 2+ , 14 BaAl 2−x Si x O 4−x N x :Eu 2+ , 15 Li 2 Sr 0.995 SiO 4−3x/2 N x :0.005Eu 2+ 16 etc.…”