Article pubs.acs.org/JPCC
Tunable Luminescence and Ce3+ → Tb3+ → Eu3+ Energy Transfer of Broadband-Excited and Narrow Line Red Emitting Y2SiO5:Ce3+, Tb3+, Eu3+ Phosphor Xinguo Zhang,*,†,‡ Liya Zhou,† Qi Pang,† Jianxin Shi,‡ and Menglian Gong‡ †
School of Chemistry and Chemical Engineering, Guangxi University, Nanning, Guangxi 530004, China State Key Laboratory of Optoelectronic Materials and Technologies, School of Chemistry and Chemical Engineering, Sun Yat-Sen University, Guangzhou, Guangdong 510275, China.
‡
ABSTRACT: The Ce3+ → Tb3+ → Eu3+ energy-transfer process enables Eu3+5D0 → 7FJ line emission to be sensitized by the allowed Ce3+ 4f1 → 5d1 absorption transition in nearultraviolet (NUV) and violet spectral regions. This energytransfer strategy is applied in Y2SiO5:Ce3+, Tb3+, Eu3+ powders, leading to line-emitting red phosphors that can be excited by short-wavelength InGaN LEDs. The blue, green, and red colors can be tuned by the ratio of Ce3+/Tb3+/Eu3+. Furthermore, the energy-transfer efficiencies and corresponding mechanisms are discussed in detail, and the thermal stability is evaluated. The results suggest that the optimal composition phosphor Y2SiO5: 0.01Ce3+, 0.50Tb3+, 0.01Eu3+, which exhibits an intense Eu3+ red 4f−4f sharp emission with a strong 4f−5d absorption band of Ce3+ at the NUV region, could serve as a potential broadbandexcited and narrow line red phosphor for NUV LEDs. As mentioned by A.A. Setlur, the Ce3+ → (Tb3+)n → Eu3+ energy-transfer (ET) scheme can produce Eu3+ phosphors that have strong absorption bands in the near-UV and violet spectral regions, making them potential candidates as downconverting phosphors for near-UV and violet LEDs.9 Some novel red phosphors, such as YBO3: Ce3+, Tb3+, Eu3+,9 Na2Y2B2O7:Ce3+, Tb3+, Eu3+,10 and Y10Al2Si3O18N4:Ce3+, Tb3+, Eu3+,11 have been synthesized by using this strategy. However, the energy-transfer mechanism of Ce3+ → Tb3+ and Tb3+ → Eu3+ has not been carefully researched in the above-mentioned case. Y2SiO5 has a wide band gap of about 7.4 eV, so doping it with activators such as Ce3+ creates an energy level structure inside the wide band gap where the 5d to 4f transition takes place.12 Y2SiO5: Ce3+ is an efficient luminescent material under the excitations of UV, cathode ray, as well as X-ray. From the literature it is found that Y2SiO5 has two different monoclinic crystal structures. A low-temperature (synthesized at temperatures less than 1190 °C) X1 phase (space group P21/c) and a high-temperature (synthesized at temperatures above 1190 °C with a melting temperature at 1980 °C) X2 phase (space group B2/c).12−14 According to Wang’s report, the luminescent intensity of X2Y2SiO5:Ce3+ is much stronger than that of X1-Y2SiO5:Ce3+.15,16 In this paper, luminescent properties for the X2 phase are mainly considered; thus, the formula Y2SiO5:Ce3+ is used to represent the X2 phase phosphor. To the best of our knowledge, there is no research on Ce3+ → Tb3+ → Eu3+ energy transfer in X2-Y2SiO5
1. INTRODUCTION White light-emitting diodes (LEDs) provide great superiorities such as low electric consumption, environment-friendliness, high brightness, long lifetime, good reliability, and fast response1,2 and are extensively applied in solid-state lightings.3 A white-light LED with a blue InGaN chip in combination with a yellow phosphor (YAG:Ce3+) is commercially available.4 However, such a combination exhibits a poor color rendering index (
