Malate-aided selective crystallization and luminescence comparison of tetragonal and monoclinic LaVO 4 :Eu nanocrystals

• Published in: Dalton transactions : an international journal of inorganic chemistry 2021-07, Vol.50 (29), p.10147-10158
• Main Authors: Huang, Sai, Xiahou, Junqing, Zhu, Qi, Takei, Toshiaki, Kim, Byung-Nam, Li, Ji-Guang
• Format: Article
• Language: English
• ISSN: 1477-9226; 1477-9234
• DOI: 10.1039/D1DT01644J

With malate (Mal 2− ) as a new type of chelate, tetragonal (t-) and monoclinic (m-) structured LaVO 4 :Eu crystals (∼10–60 nm) were selectively crystallized as nanosquares and nanorods via a hydrothermal reaction at 200 °C for 24 h. The effects of the Mal 2− :(La,Eu) 3+ molar ratio, solution pH and Eu 3+ content on the phase structure and crystal morphology were systematically investigated and elucidated. The competition between OH − and Mal 2− toward rare earth ions was discussed to play a critical role in phase selection, and the t-phase can only be fabricated at pH ∼ 6–8 with the assistance of Mal 2− . The optimal Eu 3+ content for luminescence was determined to be ∼5 at% under the VO 4 3− → Eu 3+ energy transfer mechanism. Experimental comparison showed that t-(La 0.95 Eu 0.05 )VO 4 ( λ ex = 275 nm, λ em = 620 nm) emits ∼5.3 times as strong as m-(La 0.95 Eu 0.05 )VO 4 does ( λ ex = 313 nm, λ em = 616 nm), while theoretical analysis revealed that the 5 D 0 level of Eu 3+ has a quantum efficiency of ∼80% for the former and ∼70% for the latter. Besides, the t- and m-(La 0.95 Eu 0.05 )VO 4 nanocrystal phosphors were analyzed to have fluorescence lifetimes of ∼1.53 ± 0.01 and 2.28 ± 0.01 ms for their 620 and 616 nm red emissions, respectively.