Guo-Hui Pan

Oxygen vacancies induce Ti ⁴⁺ clustering in m -ZrO ₂ , enabling UV-driven electron delocalization within clusters and subsequent energy transfer to isolated Ti ⁴⁺ ions.

In this paper, we report on the solvothermal preparation and detailed characterization of pristine and intentionally doped zirconium dioxide (ZrO₂) nanocrystals (NCs, ~5 nm) with Eu³⁺ or Ti⁴⁺/Eu³⁺ ions using alkoxide precursors. The results indicated that the ZrO₂ NCs were dominantly of a tetragonal phase (t-ZrO₂) with a small proportion of monoclinic ZrO₂ (m-ZrO₂). The high purity of t-ZrO₂ NCs could be synthesized with more Eu³⁺ doping. It was found that the as-obtained ZrO₂ NCs contain some naturally present Ti⁴⁺ ions originating from precursors, but were being overlooked commonly, and some carbon impurities produced during synthesis. These species showed distinct photoluminescence (PL) properties. At least two types of Eu³⁺, located at low- and high-symmetry sites (probably sevenfold and eightfold oxygen coordination), respectively, were demonstrated to build into the lattice structure of t-ZrO₂ NCs together. The cationic dopants were illustrated to be distributed non-randomly over the sites normally occupied by Zr, while Ti impurities preferentially occupied the sites near the low-symmetry site of Eu³⁺, yielding efficient energy transfer from the titanate groups to the neighboring Eu³⁺. Luminescence nanothermometry could measure temperature in a non-contact and remote way and could find great potentials in micro/nano-electronics, integrated photonics, and biomedicine. On the basis of the dual-emitting combination strategy involving the white broadband CT (Ti³⁺→O⁻) emissions of the titanate groups and red sharp Eu³⁺ emissions, t-ZrO₂:Eu³⁺ nanophosphors were demonstrated to be ratiometric self-referencing optical thermometric materials, with a working range of 130–230 K and a maxima of relative sensitivity of ~1.9% K⁻¹ at 230 K.

Deep traps are needed for electron‐trapping‐based long‐term optical storage due to its resistance to thermal erasure. Current electron trapping materials have the erasing temperatures hardly beyond 600 K, limiting its storage time. Herein, an electron trapping material containing deep traps is achieved by co‐doping Tb and Eu in Y₃Al₅O₁₂ via solid‐state reaction in reducing atmosphere. After 254 nm UV charging, strong thermoluminescence of Tb³⁺ with the glow curve peaking at 600, 693, and 765 K is observed. The comparative studies of the as‐made and the air‐annealed samples suggest that these new traps are related to the complex defects containing oxygen vacancy with adjacent Eu²⁺ and the charging process is the photoionization of Tb³⁺ with subsequent electron trapping. The 693 and 765 K thermoluminescence glow peaks in the charged sample show almost no decrease during 108 h storage in dark at room temperature. Images write‐in and read‐out via 808 nm laser stimulation are realized. Furthermore, the present phosphor also exhibits temperature‐sensitive afterglow spectra in the range of 553–803 K with the sensing span of 250 K wider than other afterglow thermometers. These findings indicate the great application potentials of Y₃Al₅O₁₂:Tb,Eu phosphor in long‐term optical storage and temperature sensing.

In conventional electron trapping optical storage phosphor, both short‐ and long‐wavelength light are needed for information write‐in and read‐out, respectively, complicating the optical storage system. Here, a Y₃Al₂Ga₃O₁₂:Pr³⁺,Eu³⁺ optical storage phosphor with Pr³⁺ as an electron donor and Eu³⁺ as an electron trap is designed, and a single wavelength write‐read scheme is demonstrated, which employs the same blue laser diode (LD) light source for both optical write‐in through two‐photon up‐conversion charging and for read‐out based on photostimulated luminescence (PSL), originated from 4f¹5d¹→4f² transition of Pr³⁺ peaked at 315 nm in UV region. A deep electron trap with the mean depth of 1.42 eV and a narrow distribution of 0.3 eV is observed in the presence of Eu³⁺ in Y₃Al₂Ga₃O₁₂:Pr³⁺, implying its long‐term storage potential. The write‐in and read‐out experiments are conducted using 450 nm blue LD light with the power density of 1 W cm⁻² for write‐in and that with a low power density of 0.02 W cm⁻² for read‐out in order to avoid the effect of up‐conversion luminescence on PSL signal. These results will advance the electron trapping optical storage scheme.

Orthorhombic ZrTiO₄ is an attractive dielectric material; its optical properties are, however, less known. In this paper, we reported on the microstructure and luminescence studies of pristine ZrTiO₄ and Eu³⁺-doped ZrTiO₄ phosphors. The results indicated that two types of TiO₆ octahedra, the isolated/ localized and coupled/delocalized, coexisted in host matrix. Eu³⁺ doping could induce oxygen vacancy defect states located below the bottom of the conduction band. Pristine ZrTiO₄ showed bright yellow luminescence via STEs recombination at defects sites at low temperatures, but significant thermal quenching occurred due to STEs migration to quenching centers at elevated temperatures. Effective host sensitized energy transfer to Eu³⁺ was observed in ZrTiO₄:Eu³⁺ phosphors and yielded the red characteristic emissions of Eu³⁺. Anomalous STEs luminescence enhancement and spectral blue-shift in the excitation spectra with higher Eu^{3 +} concentration appeared and were explained by considering three factors: competitive absorption between electron transitions from the top of the valence band to the defect states and host conduction band, Eu³⁺ doping driving the production of more isolated TiO₆ octahedra, and energy back-transfer from Eu³⁺ activators to other titanate groups. On the basis of the dual-emitting combination strategy involving host STEs and Eu³⁺ luminescence, ZrTiO₄:Eu³⁺ phosphors were demonstrated to be ratiometric self-referencing optical thermometric materials, with a working range of 153–313 K and a maxima of relative sensitivity to ~1.1% K⁻¹ at 243 K.

We realized a high relative sensitivity (4.12% °C ⁻¹ ) thermometer based on the afterglow intensity ratio (AIR) in a persistent phosphor using afterglow and thermal quenching models.

Broadband near-infrared (NIR) phosphor-converted light-emitting diodes (pc-LEDs) are essential to integrate near-infrared spectrometers into mobile devices for the rapid and noninvasive detection of biological components. However, efficient broadband NIR phosphors with a peak emission wavelength longer than 800 nm are deficient. In this study, CaMgGe₂O₆:Cr³⁺ phosphor was prepared by a high-temperature solid-state reaction. The phosphor doped with 0.02Cr³⁺ showed an emission band at 845 nm with a broad bandwidth of 160 nm and a high quantum yield of 84% under 450 nm excitation. The broadband NIR pc-LED was fabricated using CaMgGe₂O₆:0.02Cr³⁺ phosphor based on a blue light-emitting diode (LED) chip. A photoelectric efficiency of 27.2% @ 10 mA and an NIR output power of 57.98 mW @ 100 mA were achieved, which are the highest values reported yet for broadband NIR pc-LEDs with a peak wavelength longer than 800 nm. Using the fabricated NIR pc-LED as the light source, the characteristic absorption spectra of some substances were obtained. All of the results indicated that the CaMgGe₂O₆:Cr³⁺ phosphor has considerable potential in near-infrared spectroscopic applications.