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On comparison of luminescence properties of La 2 Zr 2 O 7 and La 2 Hf 2 O 7 nanoparticles
Author(s) -
Gupta Santosh K.,
Abdou Maya,
Ghosh Partha S.,
Zuniga Jose P.,
Manoharan Ezhilarasan,
Kim HyeongJun,
Mao Yuanbing
Publication year - 2020
Publication title -
journal of the american ceramic society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.9
H-Index - 196
eISSN - 1551-2916
pISSN - 0002-7820
DOI - 10.1111/jace.16693
Subject(s) - luminescence , radioluminescence , materials science , dopant , density functional theory , nanoparticle , excited state , doping , chemical physics , atomic physics , nanotechnology , optoelectronics , chemistry , computational chemistry , physics , optics , scintillator , detector
Unveiling the underlying mechanisms of properties of functional materials, including the luminescence differences among similar pyrochlores A 2 B 2 O 7 , opens new gateways to select proper hosts for various optoelectronic applications by scientists and engineers. For example, although La 2 Zr 2 O 7 (LZO) and La 2 Hf 2 O 7 (LHO) pyrochlores have similar chemical compositional and crystallographic structural features, they demonstrate different luminescence properties both before and after doped with Eu 3+ ions. Based on our earlier work, LHO‐based nanophosphors display higher photo‐ and radioluminescence intensity, higher quantum efficiency, and longer excited state lifetime compared to LZO‐based nanophosphors. Moreover, under electronic O 2− →Zr 4+ /Hf 4+ transition excitation at 306 nm, undoped LHO nanoparticles (NPs) have only violet blue emission, whereas LZO NPs show violet blue and red emissions. In this study, we have combined experimental and density functional theory (DFT) based theoretical calculation to explain the observed results. First, we calculated the density of state (DOS) based on DFT and studied the energetics of ionized oxygen vacancies in the band gaps of LZO and LHO theoretically, which explain their underlying luminescence difference. For Eu 3+ ‐doped NPs, we performed emission intensity and lifetime calculations and found that the LHOE NPs have higher host to dopant energy transfer efficiency than the LZOE NPs (59.3% vs 24.6%), which accounts for the optical performance superiority of the former over the latter. Moreover, by corroborating our experimental data with the DFT calculations, we suggest that the Eu 3+ doping states in LHO present at exact energy position (both in majority and minority spin components) where oxygen defect states are located unlike those in LZO. Lastly, both the NPs show negligible photobleaching highlighting their potential for bioimaging applications. This current report provides a deeper understanding of the advantages of LHO over LZO as an advanced host for phosphors, scintillators, and fluoroimmunoassays.