Photoluminscence Spectra and Ternary CIE Colour Image of (Mg1-x-yBaxSry)1.95SiO4∶0.05Eu Phosphor Series
SUN Chuan-yao1, LUO Lan1, 2*, WANG Yu1, GUO Rui1, ZHANG Yuan-bo1
1. School of Materials Science and Engineering，Nanchang University，Nanchang 330001，China
2. Key Laboratory of Lightweight and High Strength Structural Materials of Jiangxi Province，Nanchang University，Nanchang 330001，China
Abstract：A novel (Mg1-x-yBaxSry)1.95SiO4∶0.05Eu phosphor was prepared by high-temperature solid state reaction method, including 3 binary alkaline earth ion ratio series and 3 representative ternary alkaline earth ion ratio series (Ba is constant and the Mg/Sr ratio is continuously changed, the Mg/Sr ratio is constant and the Ba content is continuously changed.). As for the 6 series, the spectral properties (excitation and emission spectra), ultraviolet (254 and 365 nm) luminescence recordings and CIE values corresponding to the color images were studied in detail. Like the way to establish a ternary phase diagram, a ternary colour image is derived from these binary and representative ternary data. It can be used to study and screen a new phosphor series in a more efficient way. The prepared phosphor series include: Mg2SiO4-Sr2SiO4, Ba2SiO4-Sr2SiO4, Mg2SiO4-Ba2SiO4, Ba atomic ratio of 0.2 (Mg/Sr atomic ratio continuously changed), Ba atomic ratio of 0.6 (Mg/Sr atomic ratio continuously changes), the atomic ratio of Mg/Sr is 1/4 (the series of continuous changes in Ba atomic content). Its corresponding spectral performance, luminescence recording, and CIE chromatic analysis at 254 nm excitation indicate that: Eu ions exist trivalent and divalent in (Mg1-x-yBaxSry)2SiO4; for the binary series (as the matrix as (Mg1-xBax)2SiO4 or (Ba1-ySry)2SiO4), with the increase of Ba atomic ratio, the phosphor gradually turns red (corresponding to Eu3+ ions 5D0→7F1 and 5D0→7F2 electron transition narrow band emission) to green (corresponding to Eu2+ ion 4fn-15d→4fn electronic transition emission broadband emission), and the former series change faster; the binary series as (Mg1-ySry)2SiO4 were red phosphors, and the red luminescence increases with the increase of Sr content. For the ternary series (Bax(Mg0.2Sr0.8)1-x)2SiO4 (Mg/Sr=1/4), as Ba ion amount increases, the phosphor gradually changes from red to green, and the rate of change is determined by the ratio of Mg/Sr equal to 0 (ie Ba2SiO4-Sr2SiO4 series) and the ratio of Mg/Sr is equal to ∝ (ie Ba2SiO4-Mg2SiO4 series); the ternary series (Ba0.2SryMg0.8-y)1.95SiO4 are also red phosphors, and (Ba0.6SryMg0.4-y)2SiO4 gradually turn blue and green with the atomic ratio of Mg/Sr increasing. The evolution of fluorescence emission at 365 nm excitation is generally consistent with that at 254 nm excitation, but the emission of green light in the same sample at 365 nm is stronger than that at 254 nm and the emission in the red band is weaker than that at 254 nm. Therefore, the contents of Ba in (Mg1-xBax)2SiO4, (Ba1-ySry)2SiO4, (Bax(Mg0.2Sr0.8)1-x)2 from red to green are 40at%, 60at%, 60at%, respectively (60at%, 80at%, 70at% at 254nm excitation), and Mg/Sr ratio from red to green in (Ba0.6SryMg0.4-y)2SiO4 is 1/4 (2/3 at 254 nm excitation). Based on this, ternary CIE colour image of Eu-doped Ba2SiO4-Mg2SiO4-Sr2SiO4 is established. It can be seen from the spectral image that the (Mg1-x-yBaxSry)1.95SiO4∶0.05Eu phosphor emits light under UV excitation, that is, the matrix component emits green near the Ba2SiO4 corner and emits red near the Mg2SiO4 or Sr2SiO4 corner. The larger the Mg/Sr ratio is, the faster the phosphor turns from red to green as the Ba atom increases. The green light emission of the same sample is stronger than the 254 nm excitation at 365 nm excitation and the red emission is weaker than the 254nm excitation. (Mg1-x-yBaxSry)1.95SiO4∶0.05Eu phosphor is Ba>80at%, and Mg>90at% (or Sr>80at%) phosphor can be used as high-efficiency green and red fluorescence, respectively; when the composition is (Mg0.8Sr0.2)1.95SiO4∶0.05Eu, (Ba0.8Mg0.16Sr0.04)1.95SiO4∶0.05Eu is the best red and green phosphor for UV excitation.
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