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A modified Judd-Ofelt theory is used in this paper to treat the electric dipole transitions within the 4f8 configuration of Tb3+ by considering the main perturbing components. Through the energy-level calculation and the strandard tensorial analysis, the explicit distances between the 4f7 5d configuration and the 5D4 state and other lower 4f8 energy levels are determined. The rare-earth ion Tb3+ substituted at Y3+ sites in KY3F10 has the site symmetry of C4v. The standard Judd-Ofelt parameters A2(10), A2(30), A4(30), A4(50), A6(50), A4(54) and A6(54) are included in the calculation together with odd-λ parameters A1(10), A3(30), A5(50) and A5(54). The fluorescence branching ratios originating from 5D4 are calculated. Compared with the experimental measurements, the modified model yields better results than the standard Judd-Ofelt theory.

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.

In this paper, Tm3+ and Dy3+ single- and double-doped nano-sized GdVO4 phosphors were prepared via a co-precipitation reaction. X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM) and photoluminescence (PL) were utilized to characterize the as-prepared samples. The XRD and FE-SEM results reveal that the samples are single phase and that the average size is about 30 nm, respectively. Under 280 nm ultraviolet excitation, Dy3+ and Tm3+ single-doped nano-sized GdVO4 phosphors show the characteristic emissions of Dy3+ (4F9/2 --> 6H15/2 and 4F9/2 -*6H13/2 transitions) and Tm3+ (1G4 --> 3H6 transition), respectively. All the luminescence results from efficient energy transfer from the GdVO4 host to the doped Dy3+ and Tm3+ ions. Moreover, the interaction types for Dy3+ and Tm3+ ions in nano-sized GdVO4 host are confirmed as exchange and electrical dipole-dipole interaction by theoretical calculation. In Tm3+ and Dy3+ co-doped nanosized GdVO4 phosphors, the luminescence intensities of Dy3+ ions increase with increasing Tm3+ ion doping concentration, which suggests that energy transfer from Tm3+ to Dy3+ ions occurs. The responding luminescence mechanisms have been proposed in this paper. Finally, in order to evaluate the luminescence of Tm3+ and Dy3+ co-doped nano-sized GdVO4 phosphors, the color coordinates were calculated.

Transparent Eu(3+)-doped borate glasses containing Ag nanoparticles and Ag aggregates with composition (40 - x) CaO-59.5B2O3-0.5Eu2O3-xAgNO3 were prepared by a simple one-step melt-quenching technique. The X-ray diffraction (XRD) patterns of the glasses reveal amorphous structural properties and no diffraction peaks belonging to metal Ag particles. Ag particles and Ag aggregates were observed from the absorption spectra. Effective energy transfers from the Ag aggregates to the Eu3+ ions were observed in the excitation spectra from monitoring the intrinsic emission of Eu3+x .5D0 --> 7F2. The glasses with higher Ag content can be effectively excited by light in a wide wavelength region, indicating that these glasses have potential application in the solid state lighting driven by semiconductor light emitting diodes (LEDs). The emission spectra of the samples with higher Ag contents exhibit plenteous spectral components covering the full visible region from violet to red, thus indicating that these glass materials possess an excellent and tunable color rendering index. The color coordinates for all the glass samples were calculated by using the intensity-corrected emission spectra and the standard data issued by the CIE (Commission International de l' Eclairage) in 1931. It was found that the color coordinates for most samples with higher Ag contents fall into the white region in the color space.

A core-shell structure with a NaYF

CaSnO3 phosphors doped with various Eu3+ concentrations are synthesized by a solid-state reaction. The crystal structure of the phosphors is identified by the XRD technique, and it is found that the pure phase CaSnO3 phosphor can be obtained when the Eu3+ doping concentration lower than 2 mol%. The emission spectra consisting of a group of sharp lines from blue to red light originating from 5D3,2,1,0 → 7FJ transitions of Eu3+ are observed in phosphors with various Eu3+ doping concentrations. The radiative lifetimes of 5D0 level are measured for the samples with various Eu3+ concentrations, and for the sample with 2 mol% Eu3+ at various temperatures. The oscillator strengths parameters (Judd–Ofelt parameters) Ωλ(λ = 2, 4, 6) of Eu3+ in CaSnO3 phosphors are calculated to be 3.21 × 10−20, 0.88 × 10−20 and 0.35 × 10−20 cm2. The photoluminescence excitation and photoluminescence spectra are measured in the temperature range 300–750 K. The thermo-dynamical behavior for 5D3, 5D2, 5D1 and 5D0 populations are analyzed based on the temperature-dependent emission spectra of 5DJ levels.

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+.

Thermal luminescence property is one of the important factors to evaluate the performance of the phosphors. In this work, a series of Er3+-doped K2La2Ti3O10 phosphors were synthesized by a sol-gel auto-combustion method. The crystal structure, surface morphology, luminescence performance, thermal stability, and temperature sensing properties were investigated in detail. All samples exhibited green emissions around 530 and 564 nm due to the 2H11/2, 4S3/2→4I15/2 transitions of Er3+ upon 383 nm excitation. The optimal doping concentration of Er3+ was about 3 mol%. Electric dipole-dipole interaction was determined to be the main mechanism for the concentration quenching of Er3+ and possible cross-relaxation routes were proposed. Thermal luminescence quenching behavior was observed from the temperature-dependent emission spectra, and the results showed that K2La2Ti3O10: Er3+ phosphors had superior thermal luminescence stability. The activation energy was determined to be about 0.188 eV. Moreover, it was found that the temperature sensitivity of Er3+ in K2La2Ti3O10: Er3+ phosphors was sensitive to the doping concentration of Er3+. The lower the concentration of Er3+ was, the higher the temperature sensitivity was.

In order to obtain the Er3+/Yb3+ co-doped Ba5Gd8Zn4O21 up-conversion phosphor material with maximum red luminous intensity, three steps are adopted as follows. Firstly, the uniform design in the experimental optimal design is used to find the reasonable doping concentration of Er3+/Yb3+. Secondly, according to the quadratic general rotary unitized design, the regression equation of the red luminescence intensity of Er3+/Yb3+ co-doped Ba5Gd8Zn4O21 under 980 nm and 1550 nm excitations is established. Finally, the optimal solution of the regression equation is obtained by genetic algorithm. The Ba5Gd8Zn4O21:Er3+/Yb3+ phosphors are prepared by a high-temperature solid-phase method. The crystal structure for each of the prepared phosphors is analyzed by X-ray diffraction, and it is confirmed that the prepared phosphor samples of Ba5Gd8Zn4O21 are all in pure phase. Using the 980 nm laser as an excitation source, the relationship between the red up-conversion luminescence intensity of the optimal sample and the operating current of the laser is studied. It is found that the red luminescence is emitted through a double-photon process by the formula fitting analysis. Using the 1550 nm laser as the excitation source, it is found that red luminescence is emitted through a three-photon process. The up-conversion emission spectrum of the optimal sample with respect to temperature is measured and discussed, and it is found that the red up-conversion luminescence intensity of the sample is weakened as the temperature increases. The optimal samples are compared with the commercial phosphors of NaYF4:Er3+/Yb3+ under the 980 nm and 1550 nm excitation respectively, the luminescence intensity of the optimal sample is much stronger than that of the commercial phosphor of NaYF4:Er3+/Yb3+. Moreover, under the same power density excitation, the red up conversion luminescence intensity of the optimal sample at 980 nm is stronger than that at 1550 nm.

The upconversion technique of rare-earth-doped glasses or crystals is a potential route for achieving short-wavelength lasers (SWLs). The optical gain is an important parameter for evaluating lasing medium performance. Therefore, upconversion luminescence in glass with composition of 70TeO2–9PbF2–10AlF3–10BaF2–1Er2O3 was demonstrated, and the small-signal optical gain was measured via an amplified spontaneous emission technique when the sample was excited with a 980 nm laser. It was found that the optical gain was as large as 4.0 dB/cm, thus indicating that this glass may be a good medium for SWLs.

Gd 2 (WO 4 ) 3 phosphors with various Er 3+ concentrations and fixed Yb 3+ concentration were synthesized via a co-precipitation method, and their crystal structure and morphology were characterized by using X-ray diffraction (XRD) and scanning electron microscopy (SEM). The concentration quenching behaviors of green up- and down-conversion emissions of Er 3+ were analyzed, and it was confirmed that the difference between quenching concentration for up- and down-conversion emissions resulted from the different population routes. The temperature sensing properties of the Gd 2 (WO 4 ) 3 :Er 3+ /Yb 3+ phosphors were studied, and it was found that the Er 3+ doping concentration slightly affected the sensitivity, and Gd 2 (WO 4 ) 3 :Er 3+ /Yb 3+ phosphors could be used in a broad temperature region for detecting temperature. Finally, the thermal effect induced by 980 nm LD irradiation was investigated, it was observed that the equilibrium temperature of Gd 2 (WO 4 ) 3 :Er 3+ /Yb 3+ sample was decided by both the excitation power and Er 3+ doping concentration.

Sub-micro sized Gd 2 (WO 4 ) 3 :Yb 3+ /Ho 3+ phosphor was synthesized via a co-precipitation reaction. The crystal structure and morphology of the phosphor were characterized by XRD and SEM. The time scanning of green and red upconversion emissions displayed that the upconversion luminescent intensities were dependent on the irradiation time and the excitation powder, which was resulted from the thermal effect induced by LD (laser diode) irradiation. The upconversion luminescence of Gd 2 (WO 4 ) 3 :Yb 3+ /Ho 3+ phosphor at different sample temperatures was studied. It was found that at room temperature the red and green upconversion emissions were 1.5- and 2-photon processes, respectively. With increasing sample temperature the 2-photon process for the red upconversion emission and 3-photon process for green upconversion emission occurred.

Persimmon-like NaLa(WO(4))(2) microarchitectures were prepared via hydrothermal process with using trisodium citrate (Na(3)Cit) as chelated reagent and characterized by X-ray diffraction (XRD), field emission scanning electron microscope (FE-SEM), photoluminescence (PL), and fluorescent dynamics. The influences of Na(3)Cit concentration, organic additivities, and reaction time on the morphologies of NaLa(WO(4))(2) phosphor were studied. The results revealed that Na(3)Cit species had double functions of strong ligand and structure-directing reagent that could efficiently control the formation of persimmon-like NaLa(WO(4))(2) microarchitectures. The possible mechanism for the growth of persimmon-like NaLa(WO(4))(2) microarchitectures was attributed to the Ostwald ripening mechanism. The energy transfer from Tb(3+) to Eu(3+) in the persimmon-like NaLa(WO(4))(2) phosphors was observed. The energy transfer efficiencies and emission colors can be tuned by changing the concentration of Eu(3+). Finally, it was deduced that the electric dipole-dipole interaction (D-D) is the main mechanism for energy transfer between Tb(3+) and Eu(3+) in the persimmon-like NaLa(WO(4))(2) phosphor.

A novel optical cooling route based on anti-Stokes fluorescence of 2H11/2 state in Er3+-doped materials was proposed. The target temperature of the cooled solid could be monitored simultaneously via spectral inspection of the two green emissions from 2H11/2 and 4S3/2 excited states of Er3+. Here Er3+-doped tellurite-germanate glasses with various compositions were prepared. The temperature sensing properties and cooling abilities were systematically analyzed. It was found that all of the samples exhibit good temperature sensing performance and the net cooling could be achieved by properly choosing host materials and pumping wavelength estimated by the spectral measurements.

Color tunable phosphors of KY3(1−x)Tb3xF10 (KY3F10:xTb3+) were synthesized by the hydrothermal (HT) approach. The luminescence consists of a group of blue and green emission lines originating from 5D3→7FJ and 5D4→7FJ transitions of Tb3+, respectively. The emitting color tunes from blue to green by gradually increasing Tb3+ concentrations, which is attributed to the enhanced 5D3–5D4 cross-relaxation (CR) between two Tb3+ ions, as described by (5D3, 7F6)–(5D4, 7F0). The CR process is analyzed based on Inokuti–Hirayama model and ascribed to the electric dipole–dipole interaction. The energy transfer critical distance and critical concentration between Tb3+ ions are evaluated to be 8.03 A and 4.61 × 1020 cm−3, respectively. Moreover, the initial transfer rate on acceptor concentration is also presented with an averaged CR coefficient.

Tb3+, Eu3+ codoped YF3 nano- and micro-crystals with the morphologies of ellipsoid-like nanoplate, spindle, sandwich-structural rhombus and nanoaggregate were synthesized through a solvothermal method. The morphologies of the prepared products can be tailored by controlling the volume ratio of ethylene glycol (EG) to H2O, solvent type or the reaction time. A possible formation mechanism of the sandwich-structural rhombus like YF3 phosphor was proposed. The emitting colors of YF3:Tb3+,Eu3+ phosphors can be easily tuned from yellowish green, yellow to orange by increasing Eu3+ concentration. The energy transfer from Tb3+ to Eu3+ in YF3 phosphors was studied. It was found that the interaction type between Tb3+ and Eu3+ is electric dipole–dipole interaction.

Nanosized Gd6WO12 phosphors containing various Er3+ concentrations and fixed Yb3+ concentration were synthesized by a co-precipitation method. The crystal structure and microscopic morphology of the obtained nanophosphors were characterized by means of X-ray diffraction (XRD) and field emission scanning electron microscopy (FE-SEM). Two-photon processes for both the green and red upconversion (UC) emissions were confirmed by analyzing the dependence of UC intensities on 980 nm laser working current. UC emission intensity changing with temperature displays different trends for the samples with different Er3+ concentrations. The experimental results indicated that thermal quenching behavior of UC luminescence could not be simply explained by crossover mechanism. The enhancement for green UC emission in the sample with higher Er3+ concentration was discussed. Finally, the Er3+ concentration dependence of UC luminescence was experimentally observed, and its mechanisms were analyzed.

Y2O3:Tb3+ nanoballs were synthesized via the urea homogeneous precipitation method (UPM). The resulting Y2O3:Tb3+ phosphors were characterized by X-ray diffraction (XRD), scanning electron microscopy, ultraviolet-visible (UV-vis) absorption spectra, and general photoluminescence spectra. The particle sizes estimated using X-ray diffractometry and scanning electron microcopy were about 50–200 nm. The emission intensity of the Y2O3:Tb3+ was low when the doping concentrations of Tb3+ were higher. The optimum concentration of Tb3+ for synthesis of Y2O3:Tb3+ nanocrystals is 1%.

Eu²⁺- and Eu³⁺-doped SrAIF₅ nanorods were synthesized via a hydrothermal process. The crystal structure and morphology of the final products were characterized by X-ray diffraction (XRD) and field emission scanning electron microscopy (FESEM). The prepared nanorods' diameters range from 40 to 50 nm, and lengths range from 400 nm to 2 µm along with the doped concentration of rare earth. The f-f transitions of Eu²⁺ can be observed in the SrAlF₅:Eu²⁺ nanorods at room temperature, and the photo-luminescent (PL) properties of SrAlF₅:Eu³⁺ nanorods are also described.

BaGd 2 ZnO 5 :Dy 3+ phosphors were synthesized by a traditional solid-state reaction. The crystal structure of the phosphors was characterized by X-ray diffraction (XRD). The blue emission (456 nm) corresponding to 4 H 15/2 → 6 H 15/2 transition was observed at higher sample temperatures, and the population mechanism of 4 H 15/2 level was assigned to the thermal excitation of 4 F 9/2 level. The fluorescence concentration quenching of 4 F 9/2 level was studied based on Van Uitert's model, and that the electric dipole–dipole interaction was confirmed to be the responsible mechanism for the energy transfer between Dy 3+ ions. Finally, the fluorescence thermal quenching of 4 F 9/2 level was studied, and the crossover effect was found to be the main physical mechanism for the fluorescence temperature quenching of Dy 3+ .

Eu 3+ -doped binary borate glasses with different metal oxide components RO (R=Ca, Sr, Ba, Zn or Pb) were prepared by melt-quenching technique. The fluorescent spectral properties of Eu 3+ in these glasses were experimentally studied. The analysis on the phonon sidebands (PSBs) indicated that RO component did not cause obvious change of the electron-phonon coupling constant (EPC). By inspecting the optical absorption edges it was found that RO could greatly affect the band gap energy, and the glass with PbO component revealed the smallest band gap energy, the glasses with ZnO, BaO and SrO showed similar band gap energy. The optical transition intensity parameters of Eu 3+ in all studied glasses were calculated, it was found that for each sample its value of Ω 2 was larger than that of Ω 4 and Ω 6 , and the sample with PbO component exhibited the smallest Ω 2 , but the Ω λ values for ZBE, CBE, BBE and SBE were very similar. These results might be helpful for the design of borate glasses.

Dy 3+ doped NaGd(MoO 4 ) 2 phosphors were synthesized by a traditional solid-state reaction route using NH 4 HF 2 as a flux. The influence of calcination temperature on the crystal structure and spectral properties was studied, and the optimum calcination temperature for producing Dy 3+ doped NaGd(MoO 4 ) 2 phosphor was experimentally confirmed. The concentration quenching of Dy 3+ fluorescence and excitation-wavelength dependent spectroscopic properties were studied. On the base of both the Van Uitert's and I-H models, the electric dipole–dipole (D–D) interaction was ascribed to be the main physical mechanism responsible for energy transfer between Dy 3+ ions. It was also discovered that the color coordinates of the Dy 3+ doped NaGd(MoO 4 ) 2 phosphor depends on the Dy 3+ doping concentration and the excitation wavelength.

Ho 3+ /Yb 3+ co-doped NaGdTiO 4 phosphors were synthesized by a solid-state reaction method. The upconversion (UC) luminescence characteristics excited by 980 nm laser diode were systematically investigated. Bright green UC emission centered at 551 nm accompanied with weak red and near infrared (NIR) UC emissions centered at 652 and 761 nm were observed. The dependence of UC emission intensity on excitation power density showed that all of green, red and NIR UC emissions are involved in two-photon process. The UC emission mechanisms were discussed in detail. Concentration dependence studies indicated that Ho 3+ and Yb 3+ concentrations had significant influences on UC luminescence intensity and the intensity ratio of the red UC emission to that of the green one. Rate equations were established based on the possible UC mechanisms and a theoretical formula was proposed to describe the concentration dependent UC emission. The UC luminescence properties of the presented material was evaluated by comparing with commercial NaYF 4 :Er 3+ , Yb 3+ phosphor, and our sample showed a high luminescence efficiency and good color performance, implying potential applications in a variety of fields.

Eu 3+ doped BaGd 2 ZnO 5 phosphor was synthesized by a traditional solid-state reaction. The crystal structure of the product was characterized by means of X-ray diffraction (XRD). The ultraviolet (UV) and vacuum ultraviolet (VUV) photoluminescence properties of the phosphor were studied. Excitation spectra inferred that efficient energy transfer from Gd 3+ to Eu 3+ exists in the BaGd 2 ZnO 5 :Eu 3+ . The visible quantum cutting process based on the Gd 3+ –Eu 3+ couple was observed in the BaGd 2 ZnO 5 :Eu 3+ phosphor. Two-step energy transfer process from Gd 3+ to Eu 3+ , viz. a cross-relaxation and a sequential transfer of the remaining excitation energy, is the mechanism responsible for visible quantum cutting in BaGd 2 ZnO 5 :Eu 3+ phosphor. Quantum cutting efficiency in BaGd 2 ZnO 5 :Eu 3+ was calculated to be around 133%.

Micro-sized NaY(MoO 4 ) 2 :Tb 3+ phosphors with dendritic morphology was synthesized by a ionic liquid-assisted hydrothermal process. X-ray diffraction (XRD) indicated that the as-prepared product is pure tetragonal phase of NaY(MoO 4 ) 2 . Field emission scanning electron microscopy (FE-SEM) images showed that the as-prepared NaY(MoO 4 ) 2 :Tb 3+ phosphors have dendritic morphology. The photoluminescent (PL) spectra displayed that the as-prepared NaY(MoO 4 ) 2 :Tb 3+ phosphors show a stronger green emission with main emission wavelength 545 nm corresponding to the 5 D 4 → 7 F 5 transition of Tb 3+ ion, and the optimal Tb 3+ doping concentration for obtaining maximum emission intensity was confirmed to be 10 mol%. Based on Van Uitert's and Dexter's models the electric dipole–dipole (D–D) interaction was confirmed to be responsible for the concentration quenching of 5 D 4 fluorescence of Tb 3+ in the NaY(MoO 4 ) 2 :Tb 3+ phosphors. The intrinsic radiative transition lifetime of 5 D 4 level is found to be 0.703 ms.

Dy 3+ -doped NaGdTiO 4 phosphors were synthesized by a solid-state reaction method. The crystal structure, spectral properties and fluorescence quenching of the phosphors were systematically studied by means of X-ray diffraction (XRD) and spectroscopy. It was found that the phosphors can be effectively excited by 281 nm ultraviolet light, and intense white light emission was observed. The white light was generated by mixing blue (483 nm) and yellow (578 nm) emissions corresponding to the transitions from 4 F 9/2 to 6 H 15/2 and 6 H 13/2 levels of Dy 3+ . The electric dipole–dipole interaction between Dy 3+ ions was identified as the main mechanism for the concentration dependent fluorescence quenching of 4 F 9/2 level. The CIE color coordinates of the phosphors were calculated to be ( x = 0.3345, y = 0.3535) in the white region under 281 nm excitation, which is very close to the E point (energy equal point, x = 0.3333, y = 0.3333). In addition, the thermal quenching behavior of 4 F 9/2 level of Dy 3+ was also discussed, and the crossover effect was confirmed to be the dominant physical mechanism responsible for the fluorescence temperature quenching of Dy 3+ in NaGdTiO 4 host.

Eu(DBM) 3 Phen/PS (DBM = dibenzoylmethide; Phen = 1,10-phenanthroline; PS = polystyrene), a novel fluorescent fiber, was synthesized through electrospinning technology. In order to analyze the fluorescent fiber Eu(DBM) 3 phen/PS, Scanning Electron Microscope (SEM), fluorescence spectra and fluorescence decay curve were measured. The optical transition intensity parameters Ω λ ( λ = 2, 4 and 6) were calculated according to the transition intensities of 5 D 0 → 7 F J (J = 2, 4 and 6). The radiative transition properties of 5 D 0 level including transition rates, fluorescence branching ratios and radiative transition lifetime were also calculated. The evaluation of the results suggested that the novel fluorescent fiber Eu(DBM) 3 Phen/PS may be a potential efficient luminescent material.

Nanocrystal Gd2(WO4)3 and Gd2WO6 phosphors doped with Dy3+ were prepared via co-precipitation method under different reaction conditions. It was found that the nanocrystal Gd2(WO4)3 and Gd2WO6 phosphors exist in the monoclinic phase, and the phosphor particles showed sphere-like and uniform shape. The concentration quenching behavior and the dependence of fluorescence lifetime on the doping concentration were studied. It was found that the electric dipole–dipole interaction is the physical mechanism for the energy transfer between Dy3+ ions in both the nanocrystal Gd2(WO4)3 and Gd2WO6 phosphors.

Gd2Mo3O9 phosphors with various Dy3+ concentrations were synthesized by a traditional solid-state reaction using Na2CO3 as a flux. The influence of reaction temperature and Dy3+-doping concentration on the crystal structure of the phosphors was examined by XRD (X-ray diffraction). The effect of Dy3+-doping concentration on the emissions of Mo–O bond and Dy3+ was experimentally investigated. The energy transfers between host and Dy3+ ions, and between Dy3+ ions were analyzed based on both the Van Uitert and I-H models. The chromatic properties of the phosphors were also discussed.

Ho3+ doped glasses with various compositions xGeO2-(80-x)TeO2-9.5ZnF2-10NaF-0.5Ho2O3 (x=0, 10, 20, 30, 40, 50, 60, 70 and 80) were prepared by a melt-quenching technique. The composition-dependent optical transition properties of Ho3+ were investigated in the framework of Judd-Ofelt theory. The emission cross sections for 5I7→5I8 transition of Ho3+ in these glasses were calculated according to McCumber theory, and their compositional dependence was discussed. A simple method was proposed in calculating the emission cross sections of 5I7→5I8 transition, and the calculation results were compared with those derived from McCumber theory. Finally, the optical gain coefficient spectra for 5I7→5I8 transition were also analyzed.

Mono-dispersed microspheres of ternary complex Eu(DBM) 3 phen (DBM=dibenzoylmethide; phen=1,10-phenanthroline) were prepared through a facile process. The obtained sample was characterized by means of X-ray powder diffraction (XRD) and scanning electron microscope (SEM). And the luminescence properties of the Eu(DBM) 3 phen were investigated by the fluorescence spectra and the fluorescence decay. According to Judd–Ofelt theory, the optical transition intensity parameters Ω λ ( λ =2, 4 and 6) were obtained to be 20.99×10 −20 , 0.98×10 −20 and 1.79×10 −20 cm 2 , respectively. The radiative transition properties of 5 D 0 level, including transition rates, branch ratios and radiative transition lifetime were calculated. As a potential material for microsphere lasers, the optical gain performance for 5 D 0 → 7 F 2 transition was also evaluated.

Flower-like Y2(MoO4)3:Dy3+ phosphors have been synthesized via a co-precipitation approach with the aid of β-cyclodextrin. The crystal structure and morphology of the phosphors were characterized by XRD (X-ray diffraction) and FE-SEM (field emission scanning electron microscopy), respectively. The excitation and emission properties of the phosphors were examined by fluorescence spectroscopy. The dependence of color coordinates on the Dy3+ doping concentration was analyzed. The energy transfer mechanism between Dy3+ ions was studied based on the Huang's theory, I-H and Van Uitert's models. It was concluded simultaneously from these three routes that the electric dipole–dipole interaction between Dy3+ ions is the main physical mechanism for the energy transfers between Dy3+.

Nd 3+ , Er 3+ single-doped and Nd 3+ /Er 3+ codoped tellurite glasses were prepared via a melt-quenching technique, and their optical transition properties were studied in the framework of Judd-Ofelt theory. The differential excited state absorption cross section from 4 I 13/2 to 4 I 11/2 was obtained based on the McCumber theory; furthermore, the optical gain coefficient spectrum for 4 I 11/2 → 4 I 13/2 transition was calculated. The energy transfers 4 F 3/2 (Nd 3+ )+ 4I 15/2 (Er 3+ )→ 4 I 9/2 (Nd 3+ )+ 4 I 9/2 (Er 3+ ) and 4 I 13/2 (Er 3+ )+ 4 I 9/2 (Nd 3+ )→ 4 I 15/2 (Er 3+ )+ 4 I 15/2 (Nd 3+ ) in the codoped sample were analyzed by using Foster-Dexter theory and Inokuti-Hirayama's model, respectively ; meanwhile, the energy transfer rates for both the energy transfer processes were confirmed. The results indicated that Nd 3+ may be a good sensitizer for Er 3+ to obtain intense mid-infrared emission, and that Nd 3+ /Er 3+ codoped tellurite glass may be a good candidate media for mid-infrared lasers.

A parametrization method is reported to calculate the electric-dipole transition intensities within the 4 f 2 configuration in LiYF4:Pr3+ by considering the main perturbing component of 4 f 5 d . On the basis of calculating the energy level of the 4 f 5 d configuration, the main 4 f 5 d components that can mix with the 4 f 2 transitional states are determined. We exhibit the calculated densities of the 4 f 5 d states which can mix with the initial and the final states of 3P0 energy level in Pr3+ doped LiYF4. Whereafter a new set of phenomenological intensity parameters, T k q , is put forward. In addition to the explicit static-coupling mechanism, the approach is extended by the non-explicit dynamic mechanism. Detailed description of the calculated method is brought out. The results of present fitting are compared with that obtained by the traditional parametrization scheme and obvious improvements are exhibited.

Ag-Eu3+ co-doped fluoroborate glass phosphors doped with various Eu3+-concentrations were prepared by a melt-quenching technique. The luminescent properties of these glass phosphors were characterized by excitation and emission spectra. Broad excitation and emission bands located, respectively, at 300-450 nm and 390-700 nm originating from silver aggregates were observed. Strong red emissions were detected under 404 nm violet light-emitting diode (LED) excitation for those Ag-Eu3+ co-doped samples. It was found that these red emissions of Eu3+ well compensated the deficiency of the red spectral components in glasses containing Ag aggregates. In addition, it was confirmed that stable white light could be achieved from the combination of a specific Ag-Eu3+ co-doped fluoroborate glass phosphor and LEDs with different output wavelengths. By adjusting the luminescence intensity ratio of the glass phosphor to the 404 nm violet LED, tunable emitting color was realized, and the studied glass phosphors showed excellent emitting color stability toward LED drive currents. Our results demonstrated that this kind of easy fabrication, low-cost, and highly stable Ag-Eu3+ co-doped fluoroborate glass phosphors had potential application in white LED.

Temperature controllable photothermal therapy (PTT) requires a nanoplatform in which the optical temperature sensor and photothermal calorifier are integrated together. To establish such a nanoplatform, in this work we designed a NaYF4:Er3+/Yb3+@NaYF4:Tm3+/Yb3+ core-shell structure, and studied on its temperature sensing and photothermal conversion. The core-shell nanoparticles were prepared via a thermal decomposition method; furthermore, their crystal structure and microscopic morphology were characterized by means of XRD and SEM/TEM. The properties of temperature sensing and excitation power dependent fluorescence branching ratios were investigated. It was found that the temperature sensing could be achieved based on the fluorescence intensity ratio of green emissions from Er3+, but could not be realized by using other fluorescence intensity ratios. The photothermal conversion was demonstrated under 808 and 980 nm co-excitation, and the dependences of photothermal conversion on the excitation power and irradiation time of 808 nm laser were observed. Moreover, it was also found that the core-shell particles could effectively accelerate the evaporation of anhydrous ethanol, thus implying the photothermal conversion under single 980 nm laser excitation could also be achieved.

Transparent Eu(3+)-doped borate glasses containing Ag nanoparticles and Ag aggregates with composition (40 - x) CaO-59.5B2O3-0.5Eu2O3-xAgNO3 were prepared by a simple one-step melt-quenching technique. The X-ray diffraction (XRD) patterns of the glasses reveal amorphous structural properties and no diffraction peaks belonging to metal Ag particles. Ag particles and Ag aggregates were observed from the absorption spectra. Effective energy transfers from the Ag aggregates to the Eu3+ ions were observed in the excitation spectra from monitoring the intrinsic emission of Eu3+x .5D0 --7F2. The glasses with higher Ag content can be effectively excited by light in a wide wavelength region, indicating that these glasses have potential application in the solid state lighting driven by semiconductor light emitting diodes (LEDs). The emission spectra of the samples with higher Ag contents exhibit plenteous spectral components covering the full visible region from violet to red, thus indicating that these glass materials possess an excellent and tunable color rendering index. The color coordinates for all the glass samples were calculated by using the intensity-corrected emission spectra and the standard data issued by the CIE (Commission International de l' Eclairage) in 1931. It was found that the color coordinates for most samples with higher Ag contents fall into the white region in the color space.

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.

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.

Bulk and nanosized GdVO4:Dy3+ phosphors were prepared via a simple co-precipitation process, and their crystal structure, morphology, and spectral properties were studied. It is found that electric dipole–dipole interaction was hindered in the nanosized samples based on the analysis of the dependence of luminescent intensity on the Dy3+ doping concentration. The decay time of the 4F9/2 level in the nanosized GdVO4:2 mol% Dy3+ sample is determined to be longer than that in the 0.3 mol% Dy3+ doped bulk sample. Moreover, the fluorescent lifetime of this level in the nanosized sample is strongly dependent on the index of refraction of the medium surrounding the nanoparticles, and a 0.68 filling factor was obtained. The intrinsic radiative lifetimes and internal quantum efficiencies of the 4F9/2 level of Dy3+ in the nanosized and bulk samples were obtained, which indicate that the internal quantum efficiency of nanosized sample is higher than that of the bulk sample, but the external quantum efficiency is lower.

In this paper, a two-step synthesis method for preparing Eu3+ ion-doped Y2O3@YOF core-shell nanocrystals is introduced. Eu3+ ion-doped Y2O3@YOF core-shell nanocrystals were prepared by combining an autocombustion process with a low temperature solid state reaction. X-ray powder diffraction (XRD), field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy (EDS), photoluminescence (PL) and fluorescence decay were employed to characterize the prepared samples. The results of XRD, TEM and EDS indicated that the products prepared by this method were not a mixture of Y2O3:Eu3+ and YOF:Eu3+ nanocrystals, but Eu3+ ion-doped Y2O3@YOF core-shell nanocrystals. Compared with Y2O3:Eu3+ nanocrystals, a 20% increment in luminescence intensity was observed in the Eu3+ ion-doped Y2O3@YOF core-shell nanocrystals, thus suggesting that coating with a YOF:Eu3+-shell can efficiently block the nonradiative relaxation channels that are induced by surface defect states.

Three-dimensional (3D) nanostructured CaWO(4):Tb(3+)microspheres assembled by submicrospindles were synthesized via a mild sonochemical route from an aqueous solution of CaCl(2), TbCl(3) and Na(2)WO(4) with the aid of surfactant Polyglycol 600 (PEG-600). The crystal structure and morphology of the as-prepared products were characterized by using X-ray diffraction (XRD) and field emission scanning electron microscopy (FE-SEM). Rietveld refinement was carried out on the XRD data. The results showed that the CaWO(4):Tb(3+)nanoparticles can be formed without ultrasonic irradiation or addition of PEG-600. With continuously increasing irradiation time the submicrospindles and microspheres could be self-assembled. The central diameter and length of the submicrospindles are around 190 and 500 nm, respectively. The 3D CaWO(4):Tb(3+)nanostructured microspheres with diameter of 2-4 μm were assembled by the submicrospindles. A possible formation mechanism for the 3D-structured CaWO(4):Tb(3+)microspheres was proposed. The Photoluminescent (PL) properties of Tb(3+) ions in the nanostructured CaWO(4) microspheres were studied. The energy transfer processes in CaWO(4):Tb(3+)microspheres were analyzed. The electric dipole-dipole energy transfers related to (5)D(3) level were studied by inspecting the fluorescence decay of (5)D(3) level. The energy transfer critical distance was estimated.

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.

The spectral properties of trivalent erbium ions (Er3+) are systematically studied in a melt-quenched germanate glass (60 GeO2-20PbO-10BaO-10K2O-0.1Ag2O) containing silver (Ag) particles. Thermal treatment of the material leads to the precipitation of Ag particles as observed by transmission electron microscopy and confirmed by absorption spectrum for the obvious surface plasmon resonance peak of Ag particles. The fluorescence from Er3+ in the 10-min-annealed sample with Ag particles is found to be 4.2 times enhanced compared with the unannealed sample excited by 488-nm Ar+ laser. A comparison is made between a spectral study performed on the unannealed Er3+-doped sample and the one annealed for 20 min. The data of absorption cross section and Judd—Ofelt intensity parameters show the agreement between the two samples no matter whether there are Ag particles, indicating that the introduction of Ag particles by post-heat treatment has no effect on the crystal field environment of Er3+ ions. The fluorescence enhancement is attributed to the surface plasmon oscillations of Ag particles in germanate glass.

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.

Based on the persistent energy transfer principle, Mn2+ was introduced into a CaAl2Si2O8 : Eu2+/Dy3+ phosphor to achieve white long-lasting emissions. Eu2+, Mn2+ and Dy3+ tri-doped CaAl2Si2O8 phosphors with various Mn2+ concentrations were prepared via a solid-state reaction, and the crystal structure of the phosphors was identified by the x-ray diffraction technique. The luminescent properties of the Eu2+, Mn2+ and Dy3+ tri-doped CaAl2Si2O8 phosphors were studied. The energy transfer behaviour from Eu2+ to Mn2+ was analysed within the framework of Dexter theory. The physical mechanism of energy transfer was assigned to the electric dipole–quadrupole interaction. It was also demonstrated that the colour coordinates of the phosphors can be tuned from the blue region to the white region in the colour space. Furthermore, the afterglow decay and thermoluminescence curves were measured, indicating excellent phosphorescence properties of the current phosphors.