Lizhu He

Sensitized intense near-infrared downconversion quantum cutting three-photon luminescence phenomena of the Tm(3+) ion activator in Tm(3+)Bi(3+):YNbO(4) powder phosphor.

In present study, the intense sensitized three photon near-infrared quantum cutting luminescence of Tm(3+) ion activator in Tm(3+)Bi(3+):YNbO(4) powder phosphor is reported. It is induced both by [{(1)G(4)→(3)H(4), (3)H(6)→(3)H(5)} or {(1)G(4)→(3)H(5), (3)H(6)→(3)H(4)}] and {(3)H(4)→(3)F(4), (3)H(6)→(3)F(4)} cross-energy transfer. We found that the 1820.0 nm (3)F(4)→(3)H(6) luminescence intensity of Tm(0.08)Bi(0.01)Y(0.91)NbO(4) powder phosphor excited by 302.0 nm is 151 and 8.38 times larger, compared to Tm(0.005)Y(0.995)NbO(4) excited by 302.0 and 468.0 nm, in which the quantum cutting takes place between Tm(3+) ions and Bi(3+) ion only acts as sensitizer. To the knowledge of the authors, it is the first time that the effective Bi(3+) sensitized near-infrared quantum cutting of Tm(3+) ion activator has been reported. It can facilitate the probing of the next-generation environmentally friendly germanium solar cell.

Control of Luminescence in Eu2+-Doped Orthosilicate-Orthophosphate Phosphors by Chainlike Polyhedra and Electronic Structures

A series of Eu2+-doped orthosilicate-orthophosphate solid-solution phosphors, KxBa1.97-x(Si1-xPx)O4:0.03Eu2+, have been synthesized via the conventional solid-state reaction. Using varying compositions, the lowest-energy excitation can be tuned from 470 to 405 nm, with an emission from 515 to 423 nm. We determined how chainlike cation polyhedra controlled excitation- and emission-band features by introducing in-chain characteristic length d22 and outside-chain characteristic length d12 and that there was a nearly linear relationship between the lowest-energy-excitation position and the ratio of d22 to d12. This influence of chainlike polyhedra on luminescence can be understood through the inductive effect. Luminescent thermal properties are improved remarkably by the cosubstitution of K+ and P5+ ions for Ba2+ and Si4+ ions with a T1/2 over 200 °C. We have established the host-referred-binding-energy (HRBE) and vacuum-referred-binding-energy (VRBE) schemes for the electronic structure of the series of lanthanide-doped phosphors according to the Dorenbos model and given a thermal-quenching mechanism for this series of phosphors.

Consequence of Optimal Bonding on Disordered Structure and Improved Luminescence Properties in T-Phase (Ba,Ca)2SiO4:Eu2+ Phosphor

T-phase (Ba,Ca)2SiO4:Eu2+, showing excellent luminescent thermal stability, has a positionally disordered structure with the splitting of five atom sites, but until now the reason has remained unclear. Herein, we investigate the coordination environments of each cation site in detail to understand the origins of the atom site splitting. We find that the three cation sites in the split-atom-site model are optimally bonded with ligand O atoms compared to the unsplit-atom-site model. This atom site splitting results in larger room and smaller room for each splitting cation site, which just accommodates larger Ba2+ ions and smaller Ca2+ ions, respectively, leading to more rigid structure. Based on the X-ray diffraction data refinement, the boundary of the T-phase for (Ba1- xCa x)2SiO4 is redetermined. The Eu2+-doped T-phase (Ba,Ca)2SiO4 phosphors show excellent luminescent thermal stability, which can be attributed to optimal bonding and more rigid structure with atom site splitting. These results indicate that T-phase (Ba,Ca)2SiO4:Eu2+ phosphors have promise for practical applications.

Near Infrared Quantum Cutting Luminescence of Er 3+ /Tm 3+ Ion Pairs in a Telluride Glass

The multiphoton near-infrared, quantum cutting luminescence in Er3+/Tm3+ co-doped telluride glass was studied. We found that the near-infrared 1800-nm luminescence intensity of (A) Er3+(8%)Tm3+(0.5%):telluride glass was approximately 4.4 to 19.5 times larger than that of (B) Tm3+(0.5%):telluride glass, and approximately 5.0 times larger than that of (C) Er3+(0.5%):telluride glass. Additionally, the infrared excitation spectra of the 1800 nm luminescence, as well as the visible excitation spectra of the 522 nm and 652 nm luminescence, of (A) Er3+(8%)Tm3+(0.5%):telluride glass are very similar to those of Er3+ ions in (C) Er3+(0.5%):telluride glass, with respect to the shapes of their excitation spectral waveforms and peak wavelengths. Moreover, we found that there is a strong spectral overlap and energy transfer between the infrared luminescence of Er3+ donor ions and the infrared absorption of Tm3+ acceptor ions. The efficiency of this energy transfer {4I13/2(Er3+) → 4I15/2(Er3+), 3H6(Tm3+) → 3F4(Tm3+)} between the Er3+ and Tm3+ ions is approximately 69.8%. Therefore, we can conclude that the observed behaviour is an interesting multiphoton, near-infrared, quantum cutting luminescence phenomenon that occurs in novel Er3+-Tm3+ ion pairs. These findings are significant for the development of next-generation environmentally friendly germanium solar cells, and near-to-mid infrared (1.8–2.0 μm) lasers pumped by GaN light emitting diodes.

Correlation between the energy level structure of cerium-doped yttrium aluminum garnet and luminescent behavior at varying temperatures

Luminescent spectra of cerium-doped yttrium aluminum garnet are measured at varying temperatures. It is found that the two excitation peaks demonstrate a reverse trend as the temperature rises, and the breadth of the high-energy emission peak experiences an abrupt widening. These effects could be directly linked to the energy level scheme of Ce3+ under the crystal field of local symmetry. Moreover, an alternative fitting function is provided which could effectively resolve the emission curve.