Synthesis and Luminescence Properties of Bi³⁺-Activated K₂MgGeO₄: A Promising High-Brightness Orange-Emitting Phosphor for WLEDs Conversion

Abstract

In this article we synthesized a series of phosphors KMgGeO:Bi with high brightness for white light-emitting diodes (WLEDs) conversion and investigated their crystal structures and luminescence properties using powder X-ray diffraction, diffuse reflectance spectra, X-ray photoelectron spectroscopy, photoluminescence spectra, and absolute quantum efficiency. KMgGeO:Bi phosphor exhibits intense absorption in near-UV area and presents a broad asymmetric emission band with the main peak located at 614 nm, which was ascribed to the P → S transition of Bi. The absolute quantum efficiency of the KMgGeO:0.01Bi phosphor was measured to be 66.6%. Also, this orange emission with color chromaticity coordinates of (0.4989, 0.4400) has an excellent resistance to thermal quenching: its integrated intensity at 393 K still maintained ∼85% of the one at room temperature. The WLEDs devices with R = 93.8 were fabricated by employing KMgGeO:0.01Bi as an orange phosphor, which contains abundant red light component in its emission spectrum. The excellent luminescent performance of KMgGeO:0.01Bi suggests that it is a promising orange-emitting phosphor for near-ultraviolet WLEDs.

Tuning the Bi3+-photoemission color over the entire visible region by manipulating secondary cations modulation in the ScVxP1−xO4:Bi3+ (0 ≤ x ≤ 1) solid solution

“…Because of a naked 6s electron in the electronic configuration of [Xe]-4f 14 5d 10 6s 2 [22,[32][33][35][36][37][38], the Bi 3+ ion, depending on the specific crystal host it built into, can present the emissions broadly spanning from the UV [39], blue [40], yellow [41] and to reddish/red region [35,[32][33]42], which are analogous to the Eu 2+ , Ce 3+ , and Mn 2+ ions. As compared to the frequently reported Eu 2+ , Ce 3+ , and Mn 2+ tunable solid solutions, however, only a very limited examples of Bi 3+ emission solid solutions have been reported in the literatures, such as (Yx,Luy,Scz)VO4:Bi 3+ (yellow → reddish/red) [22], Ba3-xSrxSc4O9:Bi 3+ (blue → green) [43], and YPxV1-xO4:Bi 3+ (blue → yellow) [44].…”

Study of luminescence properties of dysprosium‐doped CaAl12O19 phosphor for white light‐emitting diodes

“…There must be less than a 30% ionic‐radii difference for substituted and doped ions, which was acceptable. The percentage radius difference can be calculated using the formula given below: where D r represents the percentage of radius difference, R h and R d represent the radius for the host and the dopant cations, and CN is the coordination number …”

“…Table shows the percentage difference ( D r ) for ionic radii between host cations and dopant ions. Because of nonavailability of data for Dy 3+ CN = 12, we used the details from CN = 9 as an appropriate approximation . By virtue of the smaller ionic‐radii difference, Dy 3+ ions favor acquisition of Ca 2+ cationic positions when compared with the variance detected for other cationic sites, as shown in the Table .…”

“…As the complete charge of two Dy 3+ ions is same as that of three Ca 2+ ions, two Dy 3+ ions would be needed to maintain the charge equilibrium. Therefore, for incorporation of every two Dy 3+ ions in CaAl 12 O 19 , one vacancy defect V″ Ca consisting of two negative charges, and two positive defects Dy • Ca would be generated. Vacancy V″ Ca would behave as an electron contributor, whereas Dy • Ca defects are electrons acceptors .…”

“…Therefore, for incorporation of every two Dy 3+ ions in CaAl 12 O 19 , one vacancy defect V″ Ca consisting of two negative charges, and two positive defects Dy • Ca would be generated. Vacancy V″ Ca would behave as an electron contributor, whereas Dy • Ca defects are electrons acceptors . This process can be expressed as follows: …”