The Er 3+ @Yb 3+ co-doped SrAl 2 B 2 O 7 phosphors were prepared by a sol-gel auto-combustion method. The components, microstructure and up-conversion (UC) properties of samples were investigated systematically. The phosphors emitted red light and green light under the excitation of 980 nm wavelength. The intensity of red emission and green emission nearly linearly decreased with increasing ambient temperatures. The red emission, green emission and their intensity ratio as a function of Er 3+ concentrations and Yb 3+ concentrations were studied in detail. The results show that 4.0% Er 3+ and 8.0% Yb 3+ doped samples can obtain the best luminescence intensity while the best light purity cannot be obtained simultaneously. The intensity of red and green emission was measured as a function of excitation power. It indicates that there was no photon avalanche mechanism for SrAl 2 B 2 O 7 : Er 3+ @Yb 3+ due to the absence of sharp change of n values. The UC luminescence corresponded to a two-photon absorption process which was illustrated by the energy transfer mechanism and the steady-state rate equations. Because of the controllable monochromatic luminescence and excellent temperature-dependent luminescence properties, the SrAl 2 B 2 O 7 : Er 3+ @Yb 3+ phosphors have potential application in the fields of non-contact temperature measurement and bio-polychromatic label.
Renping Cao,Tao Liang,Wensheng Li,Chunyan Cao,Yufeng Wen,Qianglin Hu
Sr [1−3( x + y )/2] Al 2 B 2 O 7 : x Eu 3+ , y Bi 3+ ( x = 0–5 mol% and y = 0–5 mol%) phosphors are synthesized by a solid-state reaction method in air, and their crystal structure, fluorescence lifetime, and luminescence properties are investigated. The optimal composition is determined to be (Sr 0.94 Eu 0.03 Bi 0.01 )Al 2 B 2 O 7 . The PLE band peaks within the range 200–550 nm are due to O 2− → Eu 3+ charge transfer band, 7 F 0 → 5 H 3 , 5 D 4 , 5 L 7 , 5 L 6 , 5 D 3 , 5 D 2 , and 5 D 1 transitions, respectively. The strongest PL band peak under excitation 394 nm light is at ∼615 nm owing to 5 D 0 → 7 F 2 transition of Eu 3+ ion. The PL intensity of Eu 3+ , Bi 3+ co-doped SrAl 2 B 2 O 7 phosphor is 1.3 times that of Eu 3+ doped SrAl 2 B 2 O 7 phosphor due to the energy transfer between Eu 3+ and Bi 3+ ions, which is explained by the energy level diagrams of Bi 3+ and Eu 3+ ions. The CIE chromaticity coordinates of Sr 0.955 Al 2 B 2 O 7 :0.03Eu 3+ and Sr 0.94 Al 2 B 2 O 7 :0.03Eu 3+ , 0.01Bi 3+ phosphors under excitation 394 nm light are ( x = 0.6292, y = 0.3702) and ( x = 0.6284, y = 0.3711), respectively. These phosphors will be used as reddish orange emitting phosphor candidate for white LED with ∼394 nm near ultraviolet LED chip.
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