Changkui Duan

Thermometric and optical heating bi-functional properties of upconversion phosphor Ba5Gd8Zn4O21:Yb3+/Tm3+

Yb3+/Tm3+ co-doped Ba5Gd8Zn4O21 upconversion (UC) phosphors with thermometric and optical heating properties were successfully prepared by a sol–gel process, and crystal structures of all samples were examined by X-ray diffraction (XRD). The phosphors show an intense near-infrared (NIR) and several weak visible emission peaks upon 980 nm excitation. The possible UC mechanisms and processes were proposed based on the power dependence of the upconversion luminescence (UCL) intensities, and the lifetimes of 1G4 → 3H6 blue emissions were also measured to confirm the occurrence of energy transfer (ET). Temperature sensing performances based on the Stark levels (1G4(1), 1G4(2)) of Tm3+ were evaluated by analyzing temperature-dependent UCL spectra in the range 300–510 K. The maximum sensitivity for phosphors with different UCL intensities was discussed in detail and approached approximately 0.0061 K−1 at 300 K. Furthermore, the heating effect produced by laser excitation was also measured, which caused the temperature of sample to rise from 278.8 to 321.8 K upon increasing the pump power from 638 to 1802 mW. The results indicate that Yb3+/Tm3+ co-doped Ba5Gd8Zn4O21 phosphors could be considered as potential candidates for temperature sensors and optical heaters.

What Use Are Crystal Field Parameters? A Chemist’s Viewpoint

Although first principles methods are gaining interest, the crystal field model is at present the only practicable model to analyze and simulate the energy level structures of lanthanide ions (Ln(3+)) in crystal hosts at the accuracy level of approximately 10 cm(-1). Three criteria are suggested to assess the use of energy parameters, especially crystal field parameters, from the crystal field parametrization of 4f(N) energy level data sets for the entire lanthanide ion (Ln(3+)) series, except Pm(3+). Systematic analyses have been performed upon the most complete energy level data sets available for Ln(3+) situated at sites of high symmetry in crystals of Cs(2)NaLnCl(6). This presents a stringent test for theory because the number of energy parameters is considerably reduced, and the data sets are representative and fairly complete. The results from these data set fittings are shown to comply with the three criteria put forward. First, the fittings of data sets are accurate, and a predictive capability has been employed to calculate the energy levels of Pm(3+) and to elucidate and list all of the potentially luminescent levels of Ln(3+) in the hexachloroelpasolite hosts. Second, the systematic and smooth variations of parameter values over the lanthanide series have been described by simple equations and rationalized. Third, a physical insight of the crystal field parameter variation across this series of elements has been achieved by utilizing a simple semiquantitative model considering the distributions of the 4f radial wave functions at the edge of the Ln(3+) ions, where the ligand orbitals extend. The parameter trends for an individual Ln(3+) ion have been shown to be consistent also for the Cs(2)NaLnF(6) host lattice, and predictions of the individual crystal field parameter values are made.

Optical temperature sensing properties of Yb3+–Er3+ co-doped NaLnTiO4 (Ln = Gd, Y) up-conversion phosphors

Yb3+–Er3+ ion co-doped NaLnTiO4 (Ln = Y, Gd) up-conversion (UC) phosphors were successfully synthesized by a sol–gel method. The phase purity and the structure of the samples were characterized by powder X-ray diffraction (XRD), and the optimal compositions were also determined according to their UC emission intensities. The samples emit orange light and their UC spectra were recorded with excitation by a laser diode with a 980 nm wavelength. The UC luminescence intensity could be enhanced greatly after introducing sensitizer Yb3+ ions, and the energy transfer (ET) from Yb3+ to Er3+ plays a vital role. The UC mechanism and processes responsible for the emissions were investigated and found to involve two-photon absorption. The lifetime of green emission in Er3+ singly doped and Yb3+–Er3+ co-doped samples were measured to prove the existence of ET. The temperature dependence of the fluorescence intensity ratios (FIR) for the two green UC emission bands peaked at 530 and 550 nm was studied in the range of 300–510 K under excitation by a 980 diode laser with about 4 W cm−2 power density, and the maximum sensitivity was approximately 0.0045 K−1 at 510 K for NaYTiO4 and 480 K for NaGdTiO4. This indicates that Yb3+–Er3+ ion co-doped NaLnTiO4 (Ln = Y, Gd) phosphors are potential candidates for optical temperature sensors.

Temperature sensor based on ladder-level assisted thermal coupling and thermal-enhanced luminescence in NaYF 4 : Nd 3+

NaYF4: Nd³⁺ microprisms were synthesized by a hydrothermal method. The bands of near-infrared (NIR) luminescence originating from the 4F3/2, 4F5/2 and 4F7/2 levels of Nd³⁺ ions in NaYF4: Nd³⁺ microcrystals were measured under 574.8 nm excitation at various temperatures from 323 to 673 K. The fluorescence intensity ratios (FIRs) between any two of the three bands change monotonically with temperature and agree with the prediction assuming thermal couplings. A large relative temperature sensitivity of 1.12% K⁻¹ at 500K is reached with the FIR of 4F7/2 to 4F3/2 levels. In addition, anti-Stokes fluorescence from 4F5/2 level (740 nm) and 4F5/2,7/2 levels (740 nm and 803 nm) of Nd³⁺ ions was studied meticulously under 793.8 nm and 864.2 nm excitations, respectively. The intensities were shown to be greatly enhanced as temperature increases, and the 740 nm band from 4F7/2 level at 458 K increases in intensity by 170 fold relative to that at 298 K under the 793.8 nm excitation.

Strategy for thermometry via Tm 3+ -doped NaYF 4 core-shell nanoparticles

Optical thermometers usually make use of the fluorescence intensity ratio of two thermally coupled energy levels, with the relative sensitivity constrained by the limited energy gap. Here we develop a strategy by using the upconversion (UC) emissions originating from two multiplets with opposite temperature dependences to achieve higher relative temperature sensitivity. We show that the intensity ratio of the two UC emissions, ³F(2,3) and ¹G₄, of Tm³⁺ in β-NaYF₄:20%Yb³⁺, 0.5%Tm³⁺/NaYF₄:1%Pr³⁺ core-shell nanoparticles under 980 nm laser excitation exhibits high relative temperature sensitivity between 350 and 510 K, with a maximum of 1.53%  K⁻¹ at 417 K. This demonstrates the validity of the strategy, and that the studied material has the potential for high-performance optical thermometry.

Coherent properties of single rare-earth spin qubits.

Rare-earth-doped crystals are excellent hardware for quantum storage of photons. Additional functionality of these materials is added by their waveguiding properties allowing for on-chip photonic networks. However, detection and coherent properties of rare-earth single-spin qubits have not been demonstrated so far. Here we present experimental results on high-fidelity optical initialization, efficient coherent manipulation and optical readout of a single-electron spin of Ce(3+) ion in a yttrium aluminium garnet crystal. Under dynamic decoupling, spin coherence lifetime reaches T2 = 2 ms and is almost limited by the measured spin-lattice relaxation time T1 = 4.5 ms. Strong hyperfine coupling to aluminium nuclear spins suggests that cerium electron spins can be exploited as an interface between photons and long-lived nuclear spin memory. Combined with high brightness of Ce(3+) emission and a possibility of creating photonic circuits out of the host material, this makes cerium spins an interesting option for integrated quantum photonics.

SITE SELECTIVELY EXCITED LUMINESCENCE AND ENERGY TRANSFER OF X1-Y2SIO5:EU AT NANOMETRIC SCALE

Two different types of structure called X1 and X2 are existing in Y2SiO5 at normal conditions. In X1 type, Y3+ ions occupy two sites where they are surrounded respectively by nine and seven oxygen ions, while in X2 structure, only six and seven oxygen ions are involved. Nanometric scale X1-Y2SiO5 crystals were prepared by sol-gel method with particle size around 50 nm. Site selective excitation at low temperature has shown four different luminescent centers. Two of them belong to Eu3+ embedded in X1-Y2SiO5, the other two are attributed to Y2O3:Eu phase and to a particular site on the surface. The occurrence of the latter site may be related to the nanometric size of the sample. A pronounced excitation energy transfer from site 2 to site 1 was also observed on excitation spectra. The energy transfer rate increases rapidly with increasing Eu3+ concentration and for x=0.7 in Y2−xSiO5:Eux, no fluorescence takes place in site 2 at 15 K. The lifetimes of the 5D0 levels of Eu3+ in the two sites were measured as ...

Coherence-protected quantum gate by continuous dynamical decoupling in diamond.

In order to achieve reliable quantum-information processing results, we need to protect quantum gates along with the qubits from decoherence. Here we demonstrate experimentally on a nitrogen-vacancy system that by using a continuous-wave dynamical decoupling method, we might not only prolong the coherence time by about 20 times but also protect the quantum gates for the duration of the controlling time. This protocol shares the merits of retaining the superiority of prolonging the coherence time and at the same time easily combining with quantum logic tasks. This method can be useful in tasks where the duration of quantum controlling exceeds far beyond the dephasing time.

All-in-one thermometer-heater up-converting platform YF3:Yb3+,Tm3+ operating in the first biological window

Achieving the combination of real-time diagnosis and therapy in one up-converting platform with sensitive thermometry and efficient heat production is a critical step towards photo-thermal therapy (PTT). Here, the potentiality of truncated octahedral YF3:Tm3+/Yb3+ micro-crystals as thermometers operating in the first biological window (BW-I) was evaluated on the basis of a thermo-responsive fluorescence intensity ratio (FIR) of far-red to NIR emission from completely separated 3F2,3/3H4 → 3H6 transitions. The probabilities of cross-relaxation (CR) processes related to 3F2,3/3H4 levels were greatly enhanced by increasing the Yb3+ content, leading to an increase of more than three times in the absolute sensitivity within the physiological temperature range. Photo-thermal effects were also assessed by monitoring the variation of temperature around the samples as functions of the Yb3+ dosage, excitation time and density of 980 nm laser diodes. These results offer a promising strategy to optimize the thermal sensitivity and optical heating ability, which indicates that the present UC platform has great potential applications in PTT as real-time thermometers and photo-thermal agents.

Luminescence properties of Er3+-doped transparent NaYb2F7 glass-ceramics for optical thermometry and spectral conversion

Novel Er3+-doped transparent NaYb2F7 glass-ceramics (GCs) were successfully fabricated for the first time by a conventional melt-quenching technique with subsequent heat treatment. The formation of NaYb2F7 nanocrystals (NCs) was confirmed by X-ray diffraction (XRD), transmission electron microscopy (TEM), high-resolution TEM (HRTEM), selected-area electron diffraction (SAED), and photoluminescence emission spectra. Moreover, the appearance of Stark level splitting of Er3+ emission bands and the variation of the decay curves demonstrate the accumulation of active centers into the NaYb2F7 NCs lattice. Hence, the photoluminescence emission intensities of Er3+ doped GC680 are greatly enhanced relative to those in precursor glass. Furthermore, the temperature dependent fluorescence intensity ratio (FIR) of thermally coupled emitting states (4S3/2, 2H11/2) in Er3+ doped GCs was studied under 980 nm laser excitation with a very low power density of 13 mW mm−2 to avoid the possible laser induced heating. A high temperature sensitivity of FIR of 1.36% K−1 is obtained at 300 K and the corresponding effective energy difference (ΔE) is 852 cm−1. Besides, laser induced heating at several excitation power densities was measured to evaluate the laser induced heating effect and the accuracy of temperature sensing for our sample. The GCs with relatively high sensitivity under low excitation power density are promising for temperature sensing. Moreover, the study on down-conversion (DC) spectra of the GC samples shows their ability to convert a high energy photon into two low energy photons, implying that they may also have important application as DC materials.