Spectroscopic properties of Dy3+ doped ZnO for white luminescence applications

White light-emitting ZnO:Dy3+ nanophosphors: delving into the spectroscopic parameters via Judd-Ofelt analysis

Developing a single-phase white emitting nanophosphor with high quantum efficiency has become a hotspot for scientific world. Herein, single-phase white-light emitting Zn1-xO:xDy3+ nanophosphors have been synthesized via a sonochemical method. X-ray diffraction analysis and Raman spectroscopy-based investigations confirmed the hexagonal wurtzite phase for Zn1-xO:xDy3+ nanophosphors with preferential growth along the (101) plane. Scanning electron microscopy images showed the formation of a ribbon-shaped morphology with a diameter of ∼25 nm. The emission spectra of the Dy3+-activated ZnO nanophosphors exhibited three distinct peaks, namely blue (480 nm), yellow (572 nm), and red (635 nm) emissions, under near-UV excitations related to the 4F9/2 → 6HJ (J = 15/2, 13/2, and 11/2) transitions of Dy3+ ions. The values of CIE chromaticity coordinates for the optimized phosphor (x = 0.329, y = 0.334) with correlated color temperature (CCT) of 5657 K indicated cool white-light emission from the phosphor. The thermal stability of ZnO:Dy3+ nanophosphors was probed by temperature-dependent luminescence. Quantitative evaluation of Judd-Ofelt intensity parameters, radiative parameters, luminescence decay, and quantum efficiency of Zn1-xO:xDy3+ using the J-O theory suggests that these nanophosphors are promising luminescent media for commercial white LEDs and other display devices.

Defect-assisted dynamic multicolor modulation in KLu3F10:Tb crystals for anti-counterfeiting

Excitation-dependent dynamic multicolor luminescent materials show potential for promising applications in the field of anti-counterfeiting. However, for most ultraviolet (UV)-excited lanthanide-doped materials, more than two types of activators are incorporated to realize multicolors. In this study, for the first time, KLu₃F₁₀:Tb crystals were used to realize excitation-dependent multicolor emissions. The morphology was modified by tuning the surface-coated citric acid (CA) content. During hydrothermal reactions, fluorine vacancy defects are formed on the crystal surface, and carboxyl groups (-COOH) are coated on the crystal surface to maintain the charge balance. Under 254 nm UV excitation, typical Tb³⁺ green emissions were observed, while a strong broadband emission peaking at 442 nm appeared in addition to these Tb³⁺ emissions under 365 nm excitation. The energy transfer (ET) process between the defect state and Tb³⁺ is clarified. This work may promote the development of single-type activator-doped multicolor luminescent materials for high-level anti-counterfeiting.

Effect of (Ce, Dy) co-doping on the microstructural, optical, and photoluminescence characteristics of solution combustion synthesized ZnO nanoparticles

Solution combustion synthesized ZnO nanoparticles that were Ce doped, Dy doped or co-doped at varying dopant concentrations were characterized for their microstructural, optical, and photoluminescence (PL) characteristics. The synthesized nanoparticles matched the standard hexagonal wurtzite structure of ZnO. The lattice fringes in the high-resolution transmission electron micrographs and the bright spotty rings in the selected area electron diffraction patterns authenticated the high crystallinity of the nanoparticles. The diffuse reflectance spectroscopy resolved the energy bandgap for the undoped ZnO as 3.18 eV, which decreased upon doping and co-doping. A sharp narrow ultraviolet emission peak at ~398 nm that originated from excitonic recombination was found in the PL spectra of the nanoparticles. The visible emission peaks in the PL spectra were assigned to the f-d and f-f electron transitions of Ce³⁺ and Dy³⁺ ions, respectively, in addition to different native defects in ZnO. The visible emissions (blue, yellow, and red) improved upon (Ce, Dy) co-doping, therefore (Ce, Dy) co-doped ZnO nanoparticles can be considered a promising luminescent material for the development of energy-saving light sources.

Ca2B2O5·H2O:Tb3+ hierarchical micro–nanostructures: formation and optical properties

The morphology and phase of the calcium borates were modulated under hydrothermal conditions, and the process of energy transfer in the materials was investigated.

Structural investigations of (Mn, Dy) co-doped ZnO nanocrystals using X-ray absorption studies

EXAFS measurements on sol gel derived (Mn, Dy) co-doped ZnO nanocrystals show that oxygen vacancies are created near the Dy sites into ZnO lattice. Thus, oxygen vacancy assisted bound magnetic polarons contribute to the RTFM in the Dy doped samples.