Yuepin Zhang

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 480 nm 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: 0.28 mol. % Pr3+ and 6.02 mol. % Yb3+, and this is equivalent to 68.4% energy transfer efficiency.

Gain properties of germanate glasses singly doped with Tm3+ and Ho3+ ions

Two kinds of germanate glasses singly doped with the ion concentration of 2.0mol.%Tm3+ and 2.0mol.%Ho3+, respectively, were prepared. According to McCumber theory, the absorption and stimulated emission cross-sections corresponding to the 3H6↔3F4 transitions of Tm3+ (at 1.8 µm) and the 5I8↔5I7 transitions of Ho3+ (at 2.0 µm) were obtained, and respective gain cross-section spectra were also computed as a function of population inversion according to absorption and emission cross-sections and the ion concentrations. For Tm3+-doped germanate glasses, the maximum of the absorption, emission, and gain cross-sections reached a value higher than those reported for fluorozirconate, fluoride, and oxyfluoride glasses. For Ho3+-doped germanate glasses, the maximum of absorption, emission, and gain cross-sections reached a value higher than that reported for fluorozircoaluminate glasses. Hence, these Tm3+-doped and Ho3+-doped germanate glasses exhibited an advantage for application in mid-infrared lasers at about 1.8 and 2.0 µm wavelength.

Luminescent properties of Ce3+-doped transparent oxyfluoride glass ceramics containing BaGdF5 nanocrystals

Abstract The transparent oxyfluoride glass ceramics containing BaGdF5 nanocrystals were prepared with a composition of 42SiO2-12Na2O-16Al2O3-24BaF2-4Gd2O3-2CeF3 (mol.%) by thermal treatment technology. The typical DSC curve, X-ray diffraction (XRD) and transmission electron microscopy (TEM) patterns were measured. The transmission spectra and luminescent properties were investigated. The decay times of the Gd3+ ions at 312 nm excited with 275 nm for the Ce3+ ions doped glass and glass ceramics specimens and the energy transfer process between Gd3+ ions and Ce3+ ions were also studied. The XRD analysis and the TEM images confirmed the generation of the spherical BaGdF5 nanocrystals. Compared with the PG specimen, the intensity of the luminescence spectra of the glass ceramics specimens was apparently enhanced with the heat treatment temperature increasing, and a blue shift in the excitation spectra and the emission spectra of glass ceramics specimens was obviously observed. In the fluorescence decay curves of the Gd3+ ions, it could be obviously observed that the fluorescent intensity decays in the Ce3+ ions doped glass and glass ceramics specimens decreased rapidly with the increase of the heat treatment temperature. In addition, the energy transfer efficiency from Gd3+ ions to Ce3+ ions was also calculated.

Luminescent properties of Ce3+/Tb3+co-doped glass ceramics containing YPO4 nanocrystals for W-LEDs

Abstract Ce 3+ /Tb 3+ co-doped transparent glass ceramics containing YPO 4 nanocrystals were prepared using high temperature melting method, and their structural and luminous properties were investigated. XRD analysis and TEM images confirmed the existence of YPO 4 nanocrystals in glass ceramics. The transmission spectra proved that the glass ceramics specimens still maintained a high transparency. Then the excitation and emission spectra of the Ce 3+ and Tb 3+ single-doped and co-doped glass and glass ceramics were discussed, which proved that the glass ceramics had better luminescent properties. Under the near ultraviolet (331 nm) excitation, the broadband emission located at 385 nm was observed which was ascribed to 5d→ 2 F 5/2 and 2 F 7/2 transition of Ce 3+ ions. Several characteristic sharp peaks centered at 489, 543, 578 and 620 nm originated from the 5 D 4 to 7 F J ( J =6, 5, 4, 3) of Tb 3+ ions. The decay time of Tb 3+ ions at 543 nm and the relevant energy levels of Ce 3+ ions and Tb 3+ ions illustrated the transfer process from Ce 3+ ions to Tb 3+ ions. The best CIE chromaticity coordinate of the glass ceramics specimen was calculated as ( x =0.3201, y =0.3749), which was close to the NTSC standard values for white ( x =0.333, y =0.333). All the results suggested that the YPO 4 -based Ce 3+ /Tb 3+ co-doped glass ceramics could act as potential luminescent materials for white light-emitting diodes.

Cooperative energy transfer in Tm3+ and Yb3+ co-doped phosphate glasses

Abstract An efficient near-infrared (NIR) quantum cutting (QC) in Tm 3+ and Yb 3+ co-doped phosphate glasses was demonstrated, which involved the emission of two NIR photons from an absorbed visible photon via a cooperative energy transfer (CET) from Tm 3+ to Yb 3+ ions. Judd-Ofelt (J-O) theory was used to calculate the intensity parameters (Ω 2 , Ω 4 , Ω 6 ), the radiative transition rates ( A r ), and radiative transition lifetime (τ rad ) of Tm 3+ . Based on Inokuti-Hirayamas model, the energy transfer processes were studied and results indicated that the energy transfer of the electric dipole-dipole (Edd) was dominant in this system. Quantum efficiency related to Yb 3+ concentration was calculated, and the maximum QE efficiency reached 169.8%.

Optical Spectroscopy of Er3+ and Er3+/Yb3+ Co-doped Bi2O3-GeO2-B2O3-ZnO Glasses

Abstract The (60 - x )Bi 2 O 3 - x GeO 2 -30B 2 O 3 -10ZnO ( x = 5, 10, 20, 30 molar percent) glasses doped with Er 3+ and Er 3+ /Yb 3+ were fabricated using the melting method. The thermal stability of the glasses was studied with their DTA curves. The results show that the difference between the glass transition temperature and the crystallization onset temperature increases with the increase of GeO 2 content, indicating that the thermal stability of the glass has become better. The absorption spectra were recorded and the stimulated emission cross sections were calculated using the McCumber theory. The Ω 2 , Ω 4 , and Ω 6 parameters, the transition probability, the radiative lifetime, and the fluorescence branch ratio of Er 3+ for optical transition were calculated from their absorption spectra in terms of reduced matrix U ( t ) (λ = 2, 4, 6) character for optical transitions. The infrared emission of Er 3+ was measured upon excitation with 970 nm light and the full width at half-maximum (FWHM) was estimated from the emission spectra. The pumping efficiency and the intensity of the emission at the 1.54 μm band of Er 3+ were enhanced considerably by co-doping Yb 3+ .

Luminescent properties of Eu2+-doped BaGdF5 glass ceramics a potential blue phosphor for ultra-violet light-emitting diode

Eu2+ doped transparent oxyfluoride glass ceramics containing BaGdF5 nanocrystals were successfully fabricated by melt-quenching technique under a reductive atmosphere. The structure of the glass and glass ceramics were investigated by differential scanning calorimetry, X-ray diffraction (XRD), and transmission electron microscopy (TEM). The luminescent properties were investigated by transmission, excitation, and emission spectra. The decay time of the Gd3+ ions at 312 nm excited with 275 nm were also investigated. The results of XRD and TEM indicated the existence of BaGdF5 nanocrystals in the transparent glass ceramics. The excitation spectra of Eu2+ doped glass ceramics showed an excellent overlap with the main emission region of an ultraviolet light-emitting diode (UV-LED). Compared with the as-made glass, the emission of glass ceramics is much stronger by a factor of increasing energy transfer efficiency from Gd3+ to Eu2+ ions, the energy transfer efficiency from Gd3+ to Eu2+ ions was discussed. In a...

Optical spectroscopy and crystal-field strength of Cr3+ in various solid matrixes

Abstract The Cr 3+ :BeAl 2 O 4 crystal, Cr 3 :LiNbO 3 crystal, and ZnO-Al 2 O 3 -SiO 2 glass-ceramic were obtained by the Czochralski technique, Bridgman method, and melting processing, respectively. The optical absorption and emission spectra of the above Cr 3 -incorporated solid-state materials were recorded. The technical parameters for growing high-quality Cr 3+ :BeAl 2 O 4 and Cr 3+ :LINbO 3 crystals were obtained. The results indicate that the optical absorption and fluorescence spectra of Cr 3+ show quite a few differences in various matrixes. The sharp line emissions were observed in the Cr 3+ :BeAl 2 O 4 and Cr 3+ :LiNbO 3 crystals. The crystal-field parameters ( D q ) for Cr 3+ in different matrixes were calculated from their corresponding spectra. It is indicated that Cr 3+ :BeAl 2 O 4 and Cr 3+ :LiNbO 3 belong to the high-field site crystal, while the Cr 3+ :ZnO-Al 2 O 3 -SiO 2 glass and glass-ceramic belong to the weak-field site crystal.

Growth and Optical Spectra of Zn:Er:LiNbO3 Crystals Using Bridgman Method

Abstract The growth of LiNbO 3 single crystal with Er 3+ and Zn 2+ co-doped using Bridgman method and its characteristic absorption spectra and fluorescence spectra were reported. Large-size crystals initially containing Zn 2+ (3%) and Er 3+ (0.6%) with good optical quality were obtained using optimized conditions such as a growth rate of 0.8 ∼ 1.5 mm·h −1 and a temperature gradient of about 30 ∼ 35 °C · cm −1 across the solid-liquid interface and the sealed platinum crucible. X-ray diffraction and differential thermal analysis (DTA) were used to characterize the crystals. The results indicate that the concentration of Er 3+ ions in crystals, their absorption intensity, and their fluorescence intensity decrease from the bottom to the top in the crystals. However, for the upper part of the crystal, the up-conversion fluorescence intensity is higher than that of the lower part excited by an 800 or 970 nm pump. The effects of the crystal lattice, their structural defect and their effective segregation of Er 3+ ions were discussed with respect to the variations of the up-conversion fluorescence intensity.

Silicon-phthalocyanine bonding with SiO2 matrix and its strong optical limiting effects

Silicon-phthalocyanine (SiPc) is chemically bonded to 3-aminopropitriethoxysilane (NH2(CH2)3Si(OC2H5)3, KH550) by the nucleophilic substituted reaction between the active chlorine of silicon dichlorine phthalocyanine (SiPcCl2) and amino-group of KH550. The reacted product is hybridized with 3-glycidoxypropitrimethoxysilane (CH2OCHCH2O(CH2)3Si(OCH3)3, KH560) with sol-gel processing to form sol-gel inorganic material with good physical-chemical and optical properties. Due to tethering SiPc to the network, the aggregation of SiPc is effectively prevented in sol-gel derived matrix, and the doping concentration of SiPc in the form of monomer in the matrix is greatly enhanced. The cross-linkage of SiPcCl2 and KH550 is estimated and confirmed with FT-IR spectra. The optical limiting effects (OLE) of the gel with different content of SiPc are investigated with a frequency double Q-switched Nd3+:YAG laser of 8 nsec. pulse.