ABSTRACT
Chemical pressure generated through ion doping into crystal lattices has been proven to be conducive to exploration of new matter, development of novel functionalities, and realization of unprecedented performances. However, studies are focusing on one-time doping, and there is a lack of both advanced investigations for multiple doping and sophisticated strategies to precisely and quantitatively track the gradual functionality evolution along with progressive chemical pressure implementation. Herein, high-valent Y3+ and equal-valent Mg2+ is successively doped to replace multiple Ca sites in Ca10.5(PO4)7:Eu2+. The luminescence evolution of Eu2+ serves as an optical probe, allowing step-by-step and atomic-level tracking of the site occupation of Y3+ and Mg2+, interassociation of Ca sites, and ultimately functionality improvement. The resulting Ca8MgY(PO4)7:Eu2+ displays a record-high relative sensitivity for optical thermometry. Utilization of the environment-sensitive emission of Eu2+ as a luminescent probe has offered a unique approach to monitoring structure-functionality evolution in vivo with atomic precision, which shall also be extended to optimization of other functionalities such as ferroelectricity, conductivity, thermoelectricity, and catalytic activity through precise control over atomic diffusion in other types of substances.
ABSTRACT
The development of yellow-green phosphors for high quality white light emitting diodes (WLEDs) is critical. Herein, we successfully synthesized a mixed orthoborate-pyroborate phosphor, Ba2Sc2B4O11:Ce3+, using a high-temperature solid-state method, which exhibits bright yellow-green emission with a peak located at 540 nm and a full width at half maximum (FWHM) of 130 nm under 410 nm light excitation. In addition, the crystal structure, morphology, and thermal quenching properties of Ba2Sc2B4O11:Ce3+ were investigated in detail. The quantum yield of the optimal sample was found to be 53.3%. The concentration quenching occurred through the energy transition between the nearest-neighbor Ce3+ ions. A WLED with a low correlated color temperature (CCT = 3906 K) and a high color rendering index (Ra = 89) was prepared by coating the mixture of the phosphor Ba2Sc2B4O11:Ce3+, the commercial blue phosphor BaMgAl10O17:Eu2+ and the red phosphor CaAlSiN3:Eu2+ on a 395 nm n-UV LED chip. The results show that the yellow-green phosphor Ba2Sc2B4O11:Ce3+ could be an excellent candidate for WLEDs.
ABSTRACT
Manipulating the distribution of rare-earth activators in multiple cation lattices can achieve versatile color output for single-phased phosphor-converted white light-emitting diodes (LEDs). However, successful cases are barely reported, owing to the uncertain distribution of rare-earth activators and the special combination of three primary colors for white LEDs. Herein, we took whitlockite ß-Ca3(PO4)2 as a multiple cation lattice host to manipulate the redistribution of Eu2+ activators, and the surprising Mg2+-guided redistribution of Eu2+ activators among different Ca sites is reported for the first time to regulate the photoluminescence (PL) behavior in series Ca10.5- xMg x(PO4)7:Eu2+ phosphors. The preferential neighboring substitution of smaller Mg2+ cations in Ca(5) and Ca(4) sites triggers a discontinuous evolution of local structure along c axis and induces covalent variable Ca(1), Ca(2), and Ca(3) cation sites for the accommodation of Eu2+ activators. The unique optical feature enables the single-phased Ca9.75Mg0.75(PO4)7:Eu2+ phosphor-converted white LED to exhibit quite high color-rendering index Ra (85) and R9 (91) values. The preferential neighboring-cation substitution reported here can not only manipulate the migration of Eu2+ activators among different cation sites for tunable PL properties, but also carve out a new way for next-generation high-quality solid-state lighting.
ABSTRACT
This paper describes a simple and environmentally-friendly approach that allowed for the facile synthesis of a gadolinium-based core/shell/shell nanotube structure with a set of lanthanide ions incorporated into separated layers. In addition, by the rational design of a core/shell structure we systematically investigated the luminescence properties of different lanthanide ions in NaGdF4 host, and efficient down-conversion emission can be realized through gadolinium sublattice-mediated energy migration. The Gd(3+) ions play an intermediate role in this process. By changing the doped lanthanide ions, we generated multicolour emissions from the luminescent Ln(3+) centers via energy transfer of Ce(3+)âGd(3+)âLn(3+) and Ce(3+)âLn(3+) (Ln = Eu, Tb, Dy and Sm) in separated layers. Due to the strong absorption of ultraviolet (UV) irradiation by Ce(3+) ions, the luminescence efficiency could be enhanced after doping Ce(3+) ions in the shell. In NaGdF4:5% Eu(3+)@NaGdF4@NaGdF4:5% Ce(3+) core/shell/shell nanotubes, with increasing the NaGdF4 interlayer thickness, a gradual decrease in emission intensity was observed for the Eu(3+) activator.
