Structure–Function Correlation: Engineering High Quantum Yields in Down-Shifting Nanophosphors

Abstract

Lanthanides are routinely incorporated into quantum dots to act as down-shifting and up-converting phosphors in display and lighting applications due to their high photoluminescence quantum yields (PLQY). Recent efforts in the field have demonstrated that trivalent lanthanide, Ln­(III), incorporated into ZnAl2O4 spinel nanocrystals can achieve PLQYs of 50% for down-shifting nanophosphors using earth abundant materials. The high PLQY is surprising as the Al­(III) site in a spinel is centrosymmetric, which should lead to poor performance for these nanophosphors. However, spinels are prone to formation of an admixture of inverse and normal spinel lattices when the cation size ratio is not optimal. Such behavior can produce local cation disorder that can influence the phosphor performance. Herein, we describe the use of Tb­(III) as an optical probe to evaluate the fractional population of the inverse and normal spinel structures within Tb x ZnAl2‑x O4. The experimental data exhibits a Tb­(III) concentration dependent change in the fractional population that results in a maximum PLQY of 37% with 3.56% Tb­(III) incorporation. A decrease in the degree of inversion (cation disorder) leads to larger amounts of the cubic Fd m phase resulting in the observed photoluminescence behavior. The correlation of NMR, pXRD, and optical methods provides direct insight into the high PLQY behavior for this class of nanophosphor.

Hydrophobic Versus Hydrophilic Polyelectrolyte Multilayers for Emissive Europium Films

“…The ratio, R/O, of the intensities of the red 5 D 0 → 7 F 2 and orange 5 D 0 → F 1 transitions of Eu III can be used to gain insights into the local symmetry of the Eu III ions in the films. 50 This is because the 5 D 0 → 7 F 2 is a hypersensitive transition and can be altered by the Eu III environment. The analysis of Eu(DPA) 3 -containing films revealed that the Eu III ions remained coordinated to the DPA ligands as the R/O values for the metal complexes (3.8), PDADMA/PSS (3.6), and F-P4VP/Nafion (3.7) luminescent films were similar.…”

“…Incorporation of the [Eu­(DPA) 3 ] 3– complexes into the films did not show any significant effect on the color purity of the Eu III emission as the linewidths fwhm of the 5 D 0 → 7 F 2 were determined to be minimally broadened from 2.2(±0.1) to 2.4 nm when incorporated into the F-P4VP/Nafion and PDADMA/PSS films. The ratio, R/O, of the intensities of the red 5 D 0 → 7 F 2 and orange 5 D 0 → 7 F 1 transitions of Eu III can be used to gain insights into the local symmetry of the Eu III ions in the films . This is because the 5 D 0 → 7 F 2 is a hypersensitive transition and can be altered by the Eu III environment.…”

Why Do Relative Intensities of Charge Transfer and Intra-4f Transitions of Eu3+ Ion Invert in Yttrium Germanate Hosts? Unravelling the Underlying Intricacies from Experimental and Theoretical Investigations

“…These inferences are important for designing the phosphor for next-generation LEDs. For an efficient phosphor, it is necessary that phosphors have a strong absorption for light emitted by LED chips. − Currently, the most used strategy for the design of new phosphors is based on a trial–error approach which often results in huge consumption of money and time. Thus, by judicially tailoring the first and second coordination shell around the Eu 3+ ion in a mixed oxide, one can design a phosphor aligned with deep and near-UV LED in a rational manner.…”

Understanding the Doping Chemistry of High Oxidation States in Scheelite CaWO4 by Hydrothermal Conditions

“…The crystal size ( D ) and lattice strain (ε) of the as-obtained samples were estimated by Williamson–Hall (W–H) formula where the term β hkl is the full width at half-maximum (FWHM) of the selected diffraction peak, K is the shape factor (normally 0.9 for spherical nanoparticles), λ represents the wavelength of the X-ray, D is the crystal size, and ε is the strain. Using the (101), (200), (204), and (116) reflections from XRD patterns, D and ε values were evaluated.…”