Haiping Xia

Excitation pathway and temperature dependent luminescence in color tunable Ba5Gd8Zn4O21:Eu3+ phosphors

A series of polycrystalline Ba5Gd8Zn4O21:Eu3+ phosphors were synthesized by a solid state reaction for the first time. The crystal structures were examined by means of X-ray diffraction. The luminescence spectra and decay curves were investigated as a function of Eu3+ concentration and temperature. It was found that the luminescent color of phosphor can be adjusted from white to red with the increase of Eu3+ concentration. Interestingly, emission spectra with different 5D0/5D1,2,3 ratios were observed when excited at 276 (corresponding to the O2− → Eu3+ charge transfer band) and 395 nm (f–f transition 7F0 → 5L6). The energy transfers between Eu3+ ions in Ba5Gd8Zn4O21 have been confirmed to be resonant type via exchange interaction for the 5D0 level and electric dipole–dipole interaction for 5DJ (J = 1–3) levels. Temperature dependent measurements revealed that the crossover process is the main mechanism for quenching luminescence of the 5D0 level of Eu3+ in the Ba5Gd8Zn4O21:Eu3+ phosphors. Finally, Judd–Ofelt parameters of Eu3+ in the Ba5Gd8Zn4O21 phosphors were calculated by a facile method in the framework of the J–O theory, in which the refractive index of Ba5Gd8Zn4O21 was deduced to be about 1.95.

Microwave-assisted hydrothermal synthesis and temperature sensing application of Er3+/Yb3+ doped NaY(WO4)2 microstructures

Laurustinus shaped NaY(WO4)2 micro-particles assembled by nanosheets were synthesized via a microwave-assisted hydrothermal (MH) route. The growing mechanisms for the obtained resultants with various morphologies were proposed based on the observation of scanning electron microscopic (SEM) images. It was found that Na3Cit added into the reaction solution greatly influenced the formation and size dimension of the nano-sheets, furthermore determined assembling of the laurustinus shaped micro-particles. The temperature sensing performance of NaY(WO4)2:Er(3+)/Yb(3+) was evaluated. Thermal effect induced by the 980nm laser irradiation in laurustinus-shaped NaY(WO4)2:Er(3+)/Yb(3+) phosphor was studied. It was found that the green upconversion luminescence intensity increased in the first stage of laser irradiation, and then decreased after reaching a maximum. Based on the thermal sensing technology the laurustinus NaY(WO4)2:Er(3+)/Yb(3+) microparticles were used as thermal probe to discover thermal effect of upconversion luminescence in laurustinus NaY(WO4)2:Tm(3+)/Yb(3+) micro-particles.

Copper phthalocyanine bonding with gel and their optical properties

Abstract (Tetracarboxyphalocyaninato)copper(II), (CuPc(COOH) 4 ) is incorporated in gel by a sol–gel process with using 3-aminopropyltriethoxysilane (NH 2 (CH 2 ) 3 Si(OC 2 H 5 ) 3 , APTS) and 3-glycidoxypropl-trimethoxysilane (CH 2 OCHCH 2 O(CH 2 ) 3 Si(OCH 3 ) 3 , GPTMS) as precursors. The starting compound and the gel are in the dimer forms of copper phthalocyanine, which are identified from their UV/visible spectra. The aggregation of copper phthalocyanine dyes from sol to gel is effectively prevented by tethering them to sol–gel matrix through the reaction of CuPc(COOH) 4 on APTS. The linkage of CuPc(COOH) 4 and APTS is estimated and confirmed with FT-IR spectra. The primary optical limiting effects (OLE) of the gel induced by dimers are investigated with a frequency double Q-switched Nd 3+ :YAG laser of 8 ns pulse.

Temperature sensing and optical heating in Er3+ single-doped and Er3+/Yb3+ codoped NaY(WO4)2 particles

Temperature sensing properties and laser induced thermal effects in rare earth doped materials could inspire some critical applications in accurate temperature detection and thermal therapy. In this paper, a microwave-assisted hydrothermal method was used to synthesize rare earth doped NaY(WO4)2 microstructures. Microstructured NaY(WO4)2 samples with various morphologies were derived by controlling the amount of trisodium citrate in reaction solution. Microscopic image and crystal structure of the obtained samples were characterized by XRD, SEM and HRTEM. It was found that all the received samples exhibited pure phase, and the Cit3−/Y3+ ratio considerably influenced the morphology but the rare earth concentration did not. The temperature sensing performance for the samples with various morphologies and different rare earth concentrations was evaluated. It was confirmed that both the morphology and doping concentration slightly affected the temperature property. Furthermore, based on the temperature sensing technique of Er3+ doped materials, the 980 nm laser irradiation induced thermal effect in NaY(WO4)2 microstructures was studied. It was also found that the sample temperature was very sensitive to the sample morphology and the doping concentration of Er3+ and Yb3+.

Microwave-assisted hydrothermal synthesis and laser-induced optical heating effect of NaY(WO 4 ) 2 :Tm 3+ /Yb 3+ microstructures

Tm3+/Yb3+ codoped NaY(WO4)2 microstructures with various Tm3+ concentrations and 10 mol% Yb3+ concentration and 1 mol% Er3+/10 mol% Yb3+ codoped NaY(WO4)2 microstructure were prepared via a microwave-assisted hydrothermal reaction. The crystal structure and microscopic morphology of the products were characterized by means of XRD and FM-SEM. Er3+/Yb3+ doped NaY(WO4)2 microstructure was used as temperature sensing probe for studying on the laser heating behavior in Tm3+/Yb3+ doped NaY(WO4)2 microstructures. It was found that higher laser excitation density resulted in higher sample temperature, and the sample with higher Tm3+ doping concentration exhibited more obvious heating effect when excited by 980 nm laser. Moreover, the time scanning upconversion spectra displayed that the upconversion luminescence intensities for both the samples with low and high Tm3+ concentrations almost unchanged with 980 nm laser irradiation time when the excitation power density was lower, but decreased greatly when the excitation power density was higher, and the sample with low Tm3+ concentration displayed larger luminescence intensity change rate. This phenomenon was explained by Arrhenius’s model for the thermal quenching process.

Influence of microwave hydrothermal reaction factor on the morphology of NaY(MoO4)2 nano-/micro-structures and luminescence properties of NaY(MoO4)2:Tb3+

The reaction conditions including exterior and interior factors in hydrothermal syntheses play very important roles. In this work, the influences of pH, Cit3−/Ln3+ and MoO42−/Ln3+ on the crystal structure and morphology of NaY(MoO4)2 microstructures derived from a microwave hydrothermal synthesis were systematically studied. It was found that certain morphologies of the NaY(MoO4)2:Tb3+ particles were only formed at critical pH values, and different amounts of Na3Cit and Na2(MoO4)2 in the reaction solution functioned in opposite ways in the crystal nucleation and growth. We also proposed that the competitive equilibrium between Na3Cit and Na2(MoO4)2 was responsible for the self-assembly behavior of the NaY(MoO4)2:Tb3+ nano-/micro-crystals. Based on the possible growth mechanism of the NaY(MoO4)2 microstructures, additional Cit3−/MoO42−/Ln3+ molar ratios for preparing the target products were designed and the corresponding samples were prepared. It was proven that the self-assembly behavior of the NaY(MoO4)2:Tb3+ crystals can be successfully modified under certain Cit3−/MoO42−/Ln3+ molar ratios. We also discovered that the morphology can slightly affect the luminescence intensity of the NaY(MoO4)2:Tb3+ phosphors. The temperature and concentration quenching behaviors of the NaY(MoO4)2:Tb3+ phosphors were studied. The crossover process was found to be responsible for the temperature quenching of 5D4 fluorescence, and the electric dipole–dipole interaction was proven to be the physical nature of the concentration quenching and the fluorescence decay process.

NaYF_4:Sm^3+/Yb^3+@NaYF_4:Er^3+/Yb^3+ core-shell structured nanocalorifier with optical temperature probe

A core-shell structure with a NaYF4:Sm3+/Yb3+ core for photothermal conversion nanocalorifier and a NaYF4:Er3+/Yb3+ shell as temperature probe for potential applications in photothermal therapy (PTT) were synthesized by a thermal decomposition technique of rare-earth oleate complexes. The optical temperature reading-out property for the NaYF4:Sm3+/Yb3+@NaYF4:Er3+/Yb3+ core-shell structure was systematically investigated and it was found that in comparison with pure NaYF4:Er3+/Yb3+ particles, the temperature sensing performance of the NaYF4:Er3+/Yb3+ shell did not become worse due to the presence of NaYF4:Sm3+/Yb3+ core. Furthermore, the photothermal conversion behavior for core-shell nanoparticles was successfully examined by dint of temperature sensing of the NaYF4:Er3+/Yb3+ shell, and it was found that an excitation-power-density-dependent temperature increase of up to several tens degrees can be achieved. All the experimental results suggested that the core-shell structure may be an excellent nanocalorifier candidate for advanced temperature-controllable PTT.

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.

Highly efficient up-conversion luminescence in Er 3+ /Yb 3+ co-doped Na 5 Lu 9 F 32 single crystals by vertical Bridgman method

Er3+/Yb3+ co-doped Na5Lu9F32 single crystals with different concentrations of Yb3+ ions were prepared to investigate their phase structure, up-conversion (UC) properties and mechanism of UC luminescence by Bridgman method. Under 980u2009nm near-infrared (NIR) excitation, three sharp UC emission bands topping at green ~525u2009nm, ~548u2009nm and red ~669u2009nm were obtained in Er3+/Yb3+ doped Na5Lu9F32 single crystals which are attributing to the transitions of 2H11/2u2009→u20094I15/2, 4S3/2u2009→u20094I15/2 and 4F9/2u2009→u20094I15/2, respectively. The quadratic dependence of pump power on UC emission indicated that two-photon process is in charge of the transition from excited state of Yb3+ ions to lower state of Er3+ ion in Na5Lu9F32 single crystals. The long-accepted mechanism for the production of red and green emissions through up-conversion (UC) under 980u2009nm excitation in Er3+/Yb3+ co-doped materials apply in the Na5Lu9F32 host was displayed. The enhancement of the red emission was observed due to a cross-relaxation (CR) process of the form: 4F7/2u2009+u20094I11/2u2009→u20094F9/2u2009+u20094F9/2. Furthermore, an ideal yellowish green light performance could be achieved with 1.0u2009mol% Er3+ doped certain Yb3+ concentrations samples, and its external quantum efficiency approached to 6.80% under 5.5 Wcm−2 980u2009nm excitation which can be applied in developing UC displays for electro-optical devices.

Dually functioned core-shell NaYF 4 :Er 3+ /Yb 3+ @NaYF 4 :Tm 3+ /Yb 3+ nanoparticles as nano-calorifiers and nano-thermometers for advanced photothermal therapy

To realize photothermal therapy (PTT) of cancer/tumor both the photothermal conversion and temperature detection are required. Usually, the temperature detection in PTT needs complicated instruments, and the therapy process is out of temperature control in the present investigations. In this work, we attempt to develop a novel material for achieving both the photothermal conversion and temperature sensing and control at the same time. To this end, a core-shell structure with NaYF4:Er3+/Yb3+ core for temperature detection and NaYF4:Tm3+/Yb3+ shell for photothermal conversion was designed and prepared. The crystal structure and morphology of the samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Furthermore, the temperature sensing properties for the NaYF4:Er3+/Yb3+ and core-shell NaYF4:Er3+/Yb3+@NaYF4:Tm3+/Yb3+ nanoparticles were studied. It was found that the temperature sensing performance of the core-shell nanoparticles did not become worse due to coating of NaYF4:Tm3+/Yb3+ shell. The photothermal conversion behaviors were examined in cyclohexane solution based on the temperature response, the NaYF4:Er3+/Yb3+@NaYF4:Tm3+/Yb3+ core-shell nanoparticles exhibited more effective photothermal conversion than that of NaYF4:Er3+/Yb3+ nanoparticles, and a net temperature increment of about 7u2009°C was achieved by using the core-shell nanoparticles.