The crucial impact of cerium reduction on photoluminescence

Abstract

Rare earth-based inorganic phosphors are of great interest for solid-state lighting because some of them present very efficient luminescence properties. However, their performances strongly depend on several parameters. For multivalent dopants such as cerium, a widely used activator in the lighting industry, a synthesis in reducing atmosphere is often required to stabilize the dopant in its lower oxidation state. Surprisingly, this crucial step is not much considered, and the presence of the reduced state only is often assumed. However, the presence of the dopants oxidized form has been previously evidenced after such reductions. In this case, a question remains open about the impact of the Ce 3+ /Ce 4+ ratio on the materials optical properties. As an example, different CaSc 2 O 4 :Ce samples were prepared and their Ce 3+ /Ce 4+ ratios were probed by diffuse reflection and XANES. The evolution of their photoluminescence properties was investigated to rationalize the progressive reduction of dopants.

Tuning the Oxidation States of Dopants: A Strategy for the Modulation of Material Photoluminescence Properties

“…Several groups have performed XPS analysis to characterize samples doped with Ce [17,52] , Eu [24,53,54] , or Mn [30,55] ions. quantification of each valence state of a dopant can be carried out [56][57][58][59][60][61] . In that respect, Avci et al [56] reported the investigation of Eu-doped CaAl 2 O 4 material.…”

“…While EXAFS (Extended X‐ray Absorption Fine Structure) provides information on atom environment (bond lengths, neighboring element, …), the X‐ray Absorption Near Edge Spectroscopy (XANES) region is related to local atomic states. Thus, the identification and precise quantification of each valence state of a dopant can be carried out [56–61] . In that respect, Avci et al [56] .…”

“…Thus, the identification and precise quantification of each valence state of ad opantc an be carriedo ut. [56][57][58][59][60][61] In that respect, Avci et al [56] reported the investigation of Eu-doped CaAl 2 O 4 material. Both Eu 2 + and Eu 3 + signatures are highlightedo nX ANES spectra (see Figure 8), as well as the variation of the valence distribution according to the temperature of the reductive treatment.…”

Controllable Synthesis of TbIII Metal–Organic Frameworks with Reversible Luminescence Sensing for Benzaldehyde Vapor

“…Rare-earth-based optical materials with a large Stokes shift, high color purity, and strong luminescence properties have been widely used in optical devices, communication, sensing, and bioimaging. − Among them, lanthanide metal–organic frameworks (Ln-MOFs) have attracted great interest in the field of chemical sensing due to the tailorable luminescence properties and diverse energy-transfer processes derived from their editable components (organic ligands and metal ions/clusters). − Fluorescent signal changes in the sensing process gave high sensitivity and visualization to Ln-MOFs. − Up to now, Ln-MOFs have been used to detect heavy-metal ions or anions, nitroaromatic explosives, volatile organic compounds (VOCs), biomarkers, etc. − Shi’s group synthesized the novel {[Eu 2 (L) 3 (DMF) 2 ]·DMF·MeOH} n (Ln-MOF 1 ; H 2 L = 5-(4 H -1,2,4-triazol-4-yl)­benzene-1,3-dicarboxylic acid, DMF = N , N -dimethylformamide, and MeOH = methanol), which shows the red luminescence characteristic of Eu III . There is a competitive absorption between polychlorinated benzenes and Ln-MOF 1 , which prevents the “antenna effect”.…”

Machine learning identification of experimental conditions for the synthesis of single-phase white phosphors

“…This HT approach uses the ability of several dopants such as Mn or Eu to exhibit different emissions according to their oxidation states. [19,[23][24][25][26] The strategy consists in firstly synthesizing a few materials codoped with different amounts of two dopants. Then, an oxidation step under a gradient of temperature is carried out to tune the oxidation states of dopants and the resulting emissions.…”