Haochuan Jiang

Synthesis and efficient near-infrared quantum cutting of Pr3+/Yb3+ co-doped LiYF4 single crystals

Yttrium lithium fluoride single crystals doped with trivalent lanthanide ions Pr3+ and Yb3+ are prepared by an improved Bridgman method. X-ray diffraction, photoluminescence excitation, and emission spectra and decay curves are measured to investigate the structural and luminescent properties of the crystals. An efficient near-infrared quantum cutting downconversion from the crystals was observed. The downconversion involves the emission of two near-infrared photons for each blue photon absorbed at 480u2009nm via cross relaxation energy transfer from Pr3+ to Yb3+. Decay curve fitting using a modified Inokuti-Hirayama expression indicates dipole-dipole energy transfer from Pr3+ to Yb3+, which is consistent with the expected cross-relaxation scheme. The maximum quantum cutting efficiency approaches up to 168.4% in LiYF4: 0.28u2009mol. % Pr3+ and 6.02u2009mol. % Yb3+, and this is equivalent to 68.4% energy transfer efficiency.

Preparation and luminescence characteristics of LiYF4: Tm3+/Dy3+ single crystals for white-light LEDs

Tm3+/Dy3+ co-doped LiYF4 single crystals were synthesized by using vertical Bridgman method in sealed Pt crucibles. When excited by a proper UV-light, the crystals show blue emission band centered at 485xa0nm, which overlaps between the transition of Tm3+ (1G4xa0→xa03H6) and Dy3+ (4F9/2xa0→xa06H15/2) ions, and yellow band of 573xa0nm ascribed to Dy3+ (4F9/2xa0→xa06H13/2) ions. Both chromaticity coordinates and photoluminescence intensity vary with the excitation wavelengths and the concentration of rare earth dopants. A white light can be achieved from Tm3+ (0.6xa0mol%), Dy3+ (2.25xa0mol%) co-doped LiYF4 crystal with chromaticity coordinates of xxa0≈xa00.2836, yxa0≈xa00.3229, and color temperature Tcxa0=xa08419xa0K by the excitation of a 350xa0nm light. It indicates that this crystal can be a potential candidate for the UV-light excited white-light emitting diodes.

Efficient Quantum Cutting in Tb3+/Yb3+ Codoped alpha-NaYF4 Single Crystals Grown by Bridgman Method Using KF Flux for Solar Photovoltaic

Tb³⁺/Yb³⁺ codoped α-NaYF₄ single crystals with various Yb³⁺ concentrations and ~0.40 mol% Tb³⁺ are grown by Bridgman method using KF (Potassium fluoride) as flux with a temperature gradient of 70 °C/cm-90 °C/cm across the solid-liquid interface. The effect and mechanisms of KF in the growing process are studied. The crystal structure is characterized by means of XRD. The high transmission from 300 to 7350 nm and maximum phonon energy about 390 cm^-1 for the α-NaYF₄ single crystal are obtained from the measured transmission and Raman spectra, respectively. The luminescent properties of the crystals are investigated through excitation, emission spectra, and decay curves. Downconversion with emission of two near-infrared photons about 1000 nm for each blue photon at 486-nm absorption is obtained in Tb³⁺/Yb³⁺ codoped α-NaYF₄ single crystals. Moreover, the energy transfer processes is studied based on the Inokuti-Hirayama model from the measured luminescent decay curves, and the results indicated that the interaction between Tb³⁺ and Yb³⁺ is electric dipole-dipole. The maximum quantum cutting efficiency approached 174.6% in α-NaYF₄ single crystal with 0.42 mol% Tb³⁺ and 9.98 mol% Yb³⁺, making it a potential candidate for applications in silicon-based solar cells.

Luminescent properties of Eu3+-doped α-NaYF4 single crystal under NUV-excitation

Abstract This paper reports on successful synthesis of α-NaYF4 single crystal doped with Eu3+ at various concentrations by a modified Bridgman method. The crystal structure is characterized by means of X-ray diffraction. The absorption spectra, excitation spectra and emission spectra were measured to investigate the optical properties of the single crystals. An intense red emission located at 611 nm with long lifetime of 9.03 ms was observed in single crystal under the excitation of 394 nm light. It benefits from the low maximum phonon energy of α-NaYF4 single crystal matrix (390 cm−1). The CIE chromaticity coordinate of the α-NaYF4 single crystal doped Eu3+ in 4 mol% concentration was calculated (x = 0.6055, y = 0.388), which was close to the National Television Standard Committee standard values for red phosphor (x = 0.67, y = 0.33). All these spectral properties suggest that that this kind of fluoride crystal with high thermal stability and high efficiency of red emission may be used as potential red phosphors for optical devices.

Spectral properties of and energy transfer in Bi/Tm co-doped silicate glasses

Bi, Tm singly doped and Bi/Tm co-doped glasses with molar compositions of 60SiO2–20Ga2O3–15Na2O–5Al2O3 were prepared by the conventional melt-quenching method. The enhanced emission of the Tm3+:3H4→3F4 transition at 1470xa0nm, and the quenched emission of the Tm3+:3F4→3H6 transition at 1860xa0nm were observed for Bi/Tm co-doped silicate glasses under 808 nm excitation. For 980xa0nm excitation, no Tm-related emission was observed for Tm singly doped glasses, while the emission of the Tm3+:3F4→3H6 transition at 1860xa0nm was observed for Bi/Tm co-doped glasses. These results indicated that the energy transfer occurred between active Bi ions and Tm3+ in Bi/Tm co-doped silicate glasses, in which the energy corresponding to the Bi-related emission level excited the Tm3+ from 3H6 to the 3H5 level under 980xa0nm excitation, and from 3F4 to the 3H4 level under 808xa0nm excitation. The energy-transfer processes were studied on the basis of the Inokuti–Hirayama model, and the energy transfer of the electric dipole–dipole interaction was confirmed to be dominant in Bi/Tm co-doped glasses. The Bi/Tm co-doped silicate glasses may be potential materials for producing broadband optical fiber amplifiers and tunable lasers.

The near constant loss dynamic mode in metallic glass

The near constant loss (NCL) in relaxation spectra is a crucial dynamic phenomenon for glass-forming materials, while its underlying mechanism remains unclear and is hard to study due to the absence of characteristic time scale. We define a characteristic crossover point from both the dynamic mechanical measurements and the quasi-static tension experiments in the metallic glasses (MGs), to study the transition regime, where the NCL dynamics terminates and evolves to the initiation of the β-relaxation. It is found that such transition shows an apparent activation energy well below that of the β-relaxation. Our results also show the concomitant change of the crossover points and the NCL with aging and provide a cursory physical picture on how the NCL occurs, decays and evolves to the β- and α-relaxations in MGs.

White Light Emission From Tb 3+ /Sm 3+ Codoped LiYF 4 Single Crystal Excited by UV Light

LiYF4 single crystals codoped with Tb3+/Sm3+ ions were synthesized by the vertical Bridgman method. When excited by 374-nm ultraviolet light, the crystals emit violet-blue, blue, green, yellow, orange, and red light. The white light as a result of a combination of these emissions can be achieved from Tb3+ (1.25 mol%) and Sm3+ (2.22 mol%) codoped LiYF4 crystal with chromaticity coordinates of x = 0.3143, y = 0.3484, and color temperature Tc = 6322 K by 374-nm excitation. Both chromaticity coordinates and photoluminescence intensity vary with the concentration of rare earth dopants and the excitation wavelengths. This crystal may be a potential candidate for the UV-light excited white LED device.

Temperature dependent evolution of dynamic heterogeneity in metallic glass

Substantial efforts in theoretical and experimental studies have demonstrated that the dynamics in supercooled liquids is spatially heterogeneous. However, a complete description concerning the dynamic heterogeneity evolution from liquid to rigid glass is still lacking. Here, by a combining study of the dynamic and static mechanical responses, we quantify the characterization of dynamic heterogeneity and its temperature evolution spanning an unprecedented broad temperature range in metallic glass. We show that the dynamic heterogeneity persists from the warm liquid state into the rigid glassy state and becomes progressively pronounced with cooling, accompanied by increasing breadth of the relaxation rate dispersion.

Energy transfer and 2.0 μm emission in Tm{sup 3+}/Ho{sup 3+} co-doped α-NaYF{sub 4} single crystals

Abstract Cubic NaYF 4 single crystals co-doped with ∼1.90xa0mol% Tm 3+ and various Ho 3+ concentrations were grown by Bridgman method. The energy transfer from Tm 3+ to Ho 3+ and the optimum fluorescence emission around 2.04xa0μm of Ho 3+ ion were investigated based on the measured absorption spectra, emission spectra, emission cross section and decay curves under excitation of 800xa0nm LD. The emission intensity at 2.04xa0μm increased with the increase of Ho 3+ concentration from 0.96xa0mol% to 3.89xa0mol% when the concentration of Tm 3+ was held constantly at ∼1.90xa0mol%. Moreover, the maximum emission cross section reached 1.06xa0×xa010 −20 xa0cm 2 and the maximum fluorescence lifetime was 23.23xa0ms for Tm 3+ (1.90xa0mol%)/Ho 3+ (3.89xa0mol%) co-doped one. According to the measured lifetime of Tm 3+ single-doped and Tm 3+ /Ho 3+ co-doped samples, the maximum energy transfer efficiency of Tm 3+ : 3 F 4 level was 95.0%. Analysis on the fluorescence dynamics indicated that electric dipole–dipole is dominant for the energy transfer from Tm 3+ to Ho 3+ .