Comparative analysis on the photoluminescence properties of Cs₂BF₆:Mn⁴⁺ (B = Ge, Si, Zr, Ti) red phosphors for WLEDs

Abstract

A series of Cs2BF6:Mn4+ (B = Ge, Si, Ti, Zr) red phosphors were synthesized by a precipitation‐cation exchange route. The phase purity, morphology, and constituent were characterized by X‐ray diffraction (XRD) and scanning electron microscopy (SEM). Optical properties were investigated by photoluminescence (PL) spectra and high‐resolution PL. Temperature‐dependent PL examination at the range of both 273‐573 K and 10‐300 K was performed to investigate the emission mechanism of Mn4+ in these fluorides. The intensity for both zero‐phonon lines (ZPLs) and vibration coupled emission of Mn4+ in these four systems with different crystal structures was investigated systematically. These phosphors present bright red emission under blue light (467 nm) illumination, among which Cs2GeF6:0.1Mn4+ shows the highest emission intensity with ultrahigh quantum efficiency of 94%. The white light‐emitting diodes (WLEDs) fabricated with this sample, blue InGaN chips and commercial YAG:Ce3+ phosphor exhibited high luminous efficacy beyond 100 lm/w with high color rendering index (~88.6) and low color temperature (~3684 K).

A Reverse Strategy to Restore the Moisture‐deteriorated Luminescence Properties and Improve the Humidity Resistance of Mn4+‐doped Fluoride Phosphors

“…The ions concentration changes detected by ICP-AES in supernatant with increasing immersion and restoration time are presented in Table 1 and Table 2, respectively. For the deterioration process, when 1 g K 2 SiF 6 : Mn 4 + phosphor is placed in 10 mL deionized water, its surface will ionize and release K + , Si 4 + , F À , Mn 4 reach a threshold, a black-brown coating layer forms on the surface and the luminescent proper- ties of K SiF : Mn 4 + begins to deteriorate. As the immersion time prolongs, the black-brown coating layer becomes thicker, the elongation rate of which will become slower and slower, and less ions release into the supernatant.…”

“…To further understand the elemental composition of liquid, the restoration solution was dried to afford powder at 100°C for 12 h and then XRD test was performed. As shown in the Figure S1 in Supporting Information, the as-prepared product is mainly composed of K 4 . In a word, oxalic acid, as a restoration modifier removes impurities, restores luminescent properties as well as results in K 2 SiF 6 layer to protect the phosphor from degradation.…”

“…In recent years, Mn 4 + doped fluoride phosphors have attracted widespread attention in the fields of liquid crystal display (LCD) [1] and solid-state lighting (SSL). [2] So far, a series of Mn 4 + -doped fluoride red-emitting phosphors, such as A 2 XF 6 : Mn 4 + (A = NH 4 , Li, Na, K, Rb and Cs; X = Si, Ti, Ge, Sn, Zr and Hf), [3][4][5][6] BXF 6 (6H 2 O) : Mn 4 + (B = Ba and Zn), [7][8][9][10] A 3 MF 6 : Mn 4 + (M = Al, Ga and Sc), [1,[11][12][13] A 2 NF 7 : Mn 4 + (N = Ta and Nb), [14,15] A 2 NO x F 6-x : Mn 4 + (x = 1, N = Ta and Nb; x = 2, N = W and Mo) [16][17][18][19] and A 3 XF 7 : Mn 4 + [20] has been reported. Unfortunately, although fluoride phosphors with a narrow emission at around 630 nm exhibit unique luminescence performance under blue light excitation, the deterioration of luminescent properties as a result of obvious hydrolysis has limited their large-scale application.…”

A tunable blue–cyan dual emission phosphor in Ca4−xLu2xHf1−xGe3O12:Bi3+ via forming segregation structure for WLEDs

“…[5][6][7][8] Generally, combining YAG:Ce yellow phosphor with blue LED chips manufactures WLEDs. 2,[9][10][11] However, this combination has disadvantages on low color rendering index (CRI < 75) and a high correlated color temperature (CCT > 4500 K) due to lack of red composition in emission spectra, [12][13][14][15][16][17][18][19][20][21][22][23][24][25][26][27][28] which is not suitable for general lighting because this strong blue light is harmful to human eyes. In order to overcome this weakness, another technology of manufactured WLED device has been widely proposed, which is based on the near-ultraviolet (n-UV, 380-420 nm) emitting LED chip combined with tricolor (red, green, and blue) emitting phosphors.…”

Dual-emissive Ln3+/Mn4+ Co-doped double perovskite phosphor via site-beneficial occupation

“…In recent years, as a transition metal activator, Mn 4+ has attracted much attention due to its low cost, deep red emission and wide excitation band. [37][38][39][40] As is known, it is also very important to choose a suitable matrix as the carrier of activators. Not all matrix-doped ions can emit light, but if the matrix provides suitable sites for the doped ions to replace, then they can emit fluorescence.…”