Polarized Luminescence of Anisotropic LaPO₄:Eu Nanocrystal Polymorphs

Abstract

Lanthanide elements exhibit highly appealing spectroscopic properties that are extensively used for phosphor applications. Their luminescence contains precise information on the internal structure of the host materials. Especially, the polarization behavior of the transition sublevel peaks is a fingerprint of the crystal phase, symmetry, and defects. However, this unique feature is poorly explored in current research on lanthanide nanophosphors. We here report on a detailed investigation of the evolution of Eu luminescence during the thermally induced phase transition of LaPO nanocrystal hosts. By means of c-axis-aligned nanocrystal assemblies, we demonstrate a dramatic change of the emission polarization feature corresponding to the distinct Eu site symmetries in different LaPO polymorphs. We also show that changes of the nanocrystal structure can be identified by this spectroscopic method, with a much higher sensitivity than the X-ray diffraction analysis. This new insight into the nanostructure-luminescence relationship, associated with the unprecedented polarization characterizations, provides a new methodology to investigate phase transitions in nanomaterials. It also suggests a novel function of lanthanide emitters as orientation-sensing nanoprobes for innovative applications such as in bioimaging or microfluidics.

Theory‐Guided Defect Tuning through Topochemical Reactions for Accelerated Discovery of UVC Persistent Phosphors

“…We chose lanthanum orthophosphate as a model system for our study (Figure S1, Supporting Information), with the idea that it can exhibit various structural defects such as atomic point defects, defect complexes, and radicals, and possess large band gaps that is suitable for UVC afterglow. [30][31][32][33][34][35][36] We began by carrying out first-principles DFT calculations aimed at probing whether such defects hold potential to function as traps required for afterglow. The calculated bandgap of monoclinic LaPO 4 is 5.19 eV ( Figure S2, Supporting Information), relatively smaller than the experimental value of 6.40 eV.…”

Terras Raras: Tabela Periódica, Descobrimento, Exploração No Brasil E Aplicações

“…[78][79][80] Em particular, suas propriedades luminescentes, conferidas pelas intensas e estreitas bandas de emissão, resultantes de transições do tipo f-f, geram cores específicas em dispositivos luminescentes. 81,82 Assim, materiais luminescentes contendo terras raras possuem extensa aplicação em dispositivos de iluminação, como displays emissores e lâmpadas fluorescentes, 83,84 sendo extensamente processados na forma de luminóforos de estado sólido, [85][86][87][88][89][90][91][92][93][94][95][96][97][98][99] materiais híbridos e compostos de coordenação, [100][101][102][103][104][105][106][107][108] vidros, [109][110][111][112][113][114] híbridos magnéticos-luminescentes, 115,116 entre muitos outros. Além disso, a utilização de ferramentas teóricas para a descrição da luminescência de lantanídeos é extremamente útil para o aprimoramento e adaptação das propriedades observadas.…”

Local structure and magnetism of LaxEu1−xPO4Martel1, Rakhmatullin2, Baldoví3 et al. 2019Phys. Rev. B6030View full textAdd to dashboardCite

“…LaPO 4 and EuPO 4 as well as nine intermediate La x Eu 1−x PO 4 compositions of the solid solution were prepared by sol-gel reaction, using a procedure modified from Geisler et al [13]. In short, stoichiometric amounts of La 2 O 3 (Alfa Aesar, 99.99%) and Eu 2 O 3 (Merck, 99.99%) were dissolved in HNO 3 (Merck, 63%).…”

“…Owing to their technological and fundamental interest [1,2], lanthanide orthophosphates with the monazite crystalline structure (Ln = La to Gd) have been extensively studied over the past decades. The La x Eu 1−x PO 4 solid solutions represent an important class of these materials, being luminescent [3][4][5] and being considered as potential matrices for encapsulation of nuclear materials due to their high resistance to radiation damage [6,7]. For this latter purpose, Eu 3+ is, indeed, often used as a surrogate for Am 3+ to monitor the structural modifications resulting from ion substitutions, as the two cations have similar outer electronic configuration (n f 6 , n = 4 for Eu 3+ and n = 5 for Am 3+ ) and ionic radii [8] (Eu 3+ = 0.947−1.12 Å and Am 3+ = 0.975−1.09 Å) [9][10][11].…”

“…For this latter purpose, Eu 3+ is, indeed, often used as a surrogate for Am 3+ to monitor the structural modifications resulting from ion substitutions, as the two cations have similar outer electronic configuration (n f 6 , n = 4 for Eu 3+ and n = 5 for Am 3+ ) and ionic radii [8] (Eu 3+ = 0.947−1.12 Å and Am 3+ = 0.975−1.09 Å) [9][10][11]. Additionally, while a solid solution can generally be formed over the whole range of composition [12,13], in the focus are those with low rare-earth contents [1,4] as a high solubility in a LaPO 4 matrix does not occur for all lanthanide [14,15] or actinide [16][17][18] cations.…”