•The polyethylenimine (PEI) coated sample is prepared by one pot solvothermal method.•Good biocompatibility is achieved due to the amphipathy of PEI.•The sample displays great luminescence, which can be used for bio-imaging.•The sample has excellent potential as a nano-thermometer based on the FIR technique.Rare earth ion-doped upconversion nanoparticles (UCNPs) have become a research hotspot for their applications such as nano-thermometry and bio-imaging. Here we report one pot solvothermal synthesis of polyethylenimine (PEI) coated CaF2: 1%Er3+, 2%Yb3+ UCNPs with good water-solubility and biocompatibility. The nanoparticles show a spherical shape with an average size of 40 nm and display intense green light (Yb3+ and Er3+) under the 980 nm irradiation. The maximum sensitivity of temperature sensing in the biological temperature range is obtained to be 0.00215 K−1 using the fluorescence intensity ratio (FIR) technique. Furthermore, after the UCNPs are incubated with Hela cancer cells for 6 h, the obvious green sign from Er3+ can be observed under the excitation at 980 nm. All the experimental results imply that the PEI/CaF2: 1%Er3+, 2%Yb3+ nanoparticles are excellent candidates for nano-thermometry and have good potential for biological applications.The polyethylenimine (PEI) coated CaF2: 1%Er3+, 2%Yb3+ UCNPs are great candidates for nano-thermometry and have good potential for bio-imaging.Download high-res image (177KB)Download full-size image

•Er3+/Tm3+/Ho3+ doped NaYb(MoO4)2 phosphors show strong visible luminescence.•FIR technique of thermally coupled states (TCS) and non-TCS have been explained.•The temperature sensor has high sensitivity in wide range (323–573 K).Well-crystallized NaYb(MoO4)2 doped with lanthanide ions (Ln3+: Er3+, Tm3+ and Ho3+) are successfully synthesized by hydrothermal method with further calcination. And the samples with different morphologies are obtained by changing the pH values and the molar ratio of Ln(NO3)3/Na2MoO4 of the resultant solutions. The upconversion (UC) luminescence spectra of NaYb(MoO4)2: Ln3+ between 323 K and 573 K under 980 nm excitation exhibit temperature-dependent property. The fluorescence intensity ratio (FIR) techniques with thermally coupled states (TCS) (Er3+: 2H11/2, 4S3/2 → 4I15/2, Tm3+: 1G4(1),(2) → 3H6, Ho3+: 5F5(1),(2) → 5I8) have high sensitivity (S) values (Er3+: 0.0122 K−1 at 548 K, Tm3+: 0.0025 K−1 at 323 K and Ho3+: 0.00035 K−1 at 323 K). The non-TCS (Ho3+: 5F5, 5S2/5F4 → 5I8) is used to extend the range of S, and the slope of FIR (non-TCS)-T is the S value as high as 0.02455 K-1 in the wide temperature range from 323 K to 573 K.Download high-res image (247KB)Download full-size image

•Near-spherical La2O3 nanocrystalline are synthesized via solvothermal method with further calcination.•Optical properties of Er3+ − Yb3+ codoped La2O3 are investigated and the strongest luminescence intensity of La2O3 is doped with 1% Er3+ and 2% Yb3+.•The high temperature sensor sensitivity (0.0066 k−1 at 573 K) and optical heating property of La2O3 nanocrystalline are also been researched.•The Er3+/Yb3+ codoped La2O3 nanocrystallines has a low cell totoxicity, and the confocal images of samples in HeLa cells are also obtained.Nanostructured Yb3+/Er3+ co-doped La2O3 with intense green-light emission has been successfully synthesized by solvothermal method with further calcination. The prepared La2O3: Yb3+, Er3+ are composed of approximate spherical nanoparticles with the size of about 50 nm. Optical temperature sensing performances depended on the thermally coupled levels of Er3+ are evaluated by analyzing temperature-dependent up-conversion luminescence (UCL) spectra, and the maximum sensitivity is 0.0040 K−1 at 315 K in the physiological working temperature range (295 K–315 K). Furthermore, the heating effect is also investigated, which causes the temperature of the samples to increase from 300 to 341 K with the variation of power density from 7.08 to 26.19 W/cm2. In addition, cell toxicity experiment shows that the La2O3 has low cell cytotoxicity, and the confocal images of samples in HeLa cells are also obtained. All the results indicate that the nanostructured La2O3: Yb3+/Er3+ also may be used as fluorescent bio-imaging.Download high-res image (121KB)Download full-size image

•The Tm3+ and Yb3+ codoped BaGd2ZnO5 phosphors are synthesized by sol-gel method.•The strongest luminescence intensity of BaGd2ZnO5 is doped with 0.1% Tm3+ and 12% Yb3+.•The highest temperature sensor sensitivity of trivalent ions doped BaGd2ZnO5 is 0.0055 K−1 at 323 K.•Optical heating property of BaGd2ZnO5 under lower power density have been researched.Yb3+/Tm3+ co-doped BaGd2ZnO5 phosphors have been effectively synthesized by traditional sol-gel method. The graph of X-ray diffraction (XRD) exhibited that the obtained phosphors were pure orthorhombic phase. The morphology and composition of the samples were obtained by field emission-scanning electron microscope (FE-SEM) and the energy dispersive spectrometry (EDS). From upconversion luminance (UCL) emission spectra, the two strong blue emissions were obviously observed at 478 and 485 nm under the excitation of 980 nm. The possible energy diagram and UC mechanism were explained in detail. Optical temperature (T) sensing performances were evaluated in the temperature ranging 313 K - 573 K. And the highest sensor sensitivity calculated was 0.0055 K−1 at 323 K. Additionally, the laser excitation heating effect was also explored. The results indicated that Yb3+/Tm3+ co-doped BaGd2ZnO5 phosphors could be applied on optical temperature sensors and optical heater.

•Upconversion (UC) phosphors KY(MoO4)2: xYb3+, 2%Er3+ were synthesized via a hydrothermal method.•Optical properties of 15%Yb3+, 2%Er3+ doped KY(MoO4)2 phosphors were investigated.•The temperature sensing performances were discussed.•The heating effect of the phosphor was studied.Upconversion (UC) phosphors KY(MoO4)2: xYb3+, 2%Er3+ have been synthesized by a typical hydrothermal process. The UC luminescence, thermal sensing and optical heating properties have been investigated in the paper. From the UC luminescence spectra, the phosphors show two intense green emissions at 532 nm and 553 nm under the excitation of 980 nm, which can be used to discuss the temperature sensing performance with the temperature ranging 313–563 K. The maximum sensitivity is obtained around 0.0163 K−1 at 523 K. Additionally, the laser excitation heating effect was also explored, the lattice temperature varies from 308.2 to 426.2 K with increasing of power densities from 12.73 to 82.80 W/cm2. The experimental results indicate that the KY(MoO4)2: Yb3+/Er3+ phosphor may be used as potential material with thermometric and optical heating characters.

Tunable up-conversion luminescent material KY(MoO4)2: Yb3+, Ln3+ (Ln=Er, Tm, Ho) has been synthesized by a typical hydrothermal process. Under 980 nm laser diode (LD) excitation, the emission intensity and the corresponding luminescence colors of KY(MoO4)2: Yb3+, Ln3+ (Ln=Er, Tm, Ho) have been investigated in detail. The energy transfer from the Yb3+ sensitizer to Ho3+, Er3+ and Tm3+ activators plays an important role in the development of color-tunable single- phased phosphors. The emission intensity keep balance through control of the Ho3+ co-doping concentrations, white light was experimentally shown at KY(MoO4)2: 20 mol% Yb3+, 0.8 mol% Er3+, 0.5 mol% Tm3+, 1.0 mol% Ho3+ phosphor with further calcination at 800 °C for 4 h under 980 nm laser excitation. The color tunability, high quality of white light and high intensity of the emitted signal make these up-conversion (UC) phosphors excellent candidates for applications in solid-state lighting.

A new Eu/Tb-codoped inorganic apatite Ca5(PO4)3F luminescent thermometer has been targeted. Under ultraviolet irradiation, the Ca5(PO4)3F:Tb3+/Eu3+ samples exhibit a blue-light emission of the host matrix which might originate from the CO2− radical-related defect produced by Cit3− groups, as well as the typical green emission band of the Tb3+ ions, and a red-light emission of Eu3+. These lanthanide-based thermometers (Ca5(PO4)3F:Tb3+/Eu3+) exhibit different sensitivities ranging from different temperatures based on two emissions of Tb3+ at 548 nm and Eu3+ at 621 nm. The temperature-dependent luminescent intensity ratios ITb/IEu can be optimized by the controlled relatively doping of different amounts of Tb3+ and Eu3+ ions.

LaMgAl11O19: Yb3+/Er3+ phosphors were successfully synthesized by a conventional sol–gel method with a lower temperature. The composition and phase purity of the samples were examined by X-ray diffraction (XRD). Under 980 nm excitation, the phosphors exhibited efficient visible up-conversion (UC) emissions including strong green emission centered at 525, 545 nm, and weak red emission centered at around 657 nm, which were assigned to the 2H11/2→ 4I15/2, 4S3/2→ 4I15/2 and 4F9/2→ 4I15/2 transitions of Er3+ ions, respectively. The process involved in the UC emission was evaluated in detail by energy level diagram and the pump power dependence. To investigate the sensing application of the synthesized phosphor materials, temperature-sensing performance was studied in the temperature range of 298–573 K using the fluorescence intensity ratio technique. The maximum sensitivity was found to be approximately 0.00267 K−1, indicating its applicability as an optical temperature sensor.

Uniform and well-crystallized NaCe(MoO4)2: Er3+/Ho3+, Yb3+ up-conversion (UC) phosphors have been successfully synthesized by a facile hydrothermal route at 180 °C for 12 h at pH = 9. The crystalline phase, size and morphology were systematically characterized using powder X-ray diffraction (XRD) and field emission-scanning electron microscopy (FE-SEM). The experimental results showed that the ethylene diamine tetraacetic acid (EDTA) was a key parameter which not only determined their spacial arrangement, but also affected the size distributions of the final products. Moreover, we found that EDTA could tune the band edge absorption of the molybdate system by changing the lattice parameters, so as to realize their bicolour tunable luminescence of Er3+/Ho3+-Yb3+ co-doped NaCe(MoO4)2 for the first time. Studies of the behavior as a function of dopant concentration were all described. The different UC mechanisms of the samples with and without EDTA were systematically depicted as well. It was found that an innovative route to increase the green UC emission and simultaneously suppress red UC emission in Er3+/Ho3+-Yb3+ co-doped NaCe(MoO4)2 prepared with the assistance of 0.1 g EDTA, which enhanced the efficiency of the single green color.

Uniform and well-crystallized YPO4·0.8H2O and YPO4·0.8H2O:Tb3+, Eu3+ nanocrystals have been successfully synthesized by a facile hydrothermal method using trisodium citrate (Cit3−) as a “shape modifier”. X-ray diffraction (XRD), field emission-scanning electron microscopy (FE-SEM), high-resolution transmission electron microscopy (HRTEM) and photoluminescence (PL) spectra were used to characterize the samples. It was found that the pH of the initial solution was responsible for determining the shape of the final products. In addition, the YPO4·0.8H2O samples prepared by Cit3−-assisted hydrothermal synthesis exhibited an intense and bright blue emission. Characterized with Fourier transform infrared (FT-IR) spectra and electron paramagnetic resonance (EPR) spectra, the carbon-related impurities induced by trisodium citrate (Cit3−) in the hydrothermal process were confirmed and confirmed that the paramagnetic defects relating to the luminescence properties existed in the luminescent YPO4·0.8H2O nanocrystals. More interestingly, the YPO4·0.8H2O:Tb3+, Eu3+ samples could be effectively excited with 380 nm and the luminescence colors of YPO4·0.8H2O:Tb3+, Eu3+ nanocrystals can be easily tuned by changing the concentration of Eu3+ ions due to an efficient energy transfer from Tb3+ to Eu3+. These results revealed that the combination of the defect luminescence and rare earth-doping emission in YPO4·0.8H2O:Tb3+, Eu3+ nanocrystals could result in tunable emission in a large color gamut, which may be potentially applied in fields such as solid state lighting and field emission displays.

Trivalent rare-earth (RE3+ = Eu3+, Tb3+) ion activated KLa(MoO4)2 microspheres have been synthesized at 180 °C via a facile hydrothermal route without using any templates, surfactant, or other organic additives. X-ray diffraction (XRD), field emission-scanning electron microscopy (FE-SEM), photoluminescence (PL), and photoluminescent excitation spectra (PLE) were employed to characterize the samples. It is found that the pH value in the initial solution is responsible for crystal phase, shape determination and emission intensity of final products. The possible formation mechanism for products with uniform spheres has been presented. Furthermore, a systematic study on the photoluminescence of RE3+ (RE3+ = Eu3+, Tb3+) doped KLa(MoO4)2 samples has been explored in order to obtain the multicolor tunable emission by varying the Tb3+/Eu3+ ratio. The tunable luminescence may be potentially applied in fields such as solid state lighting and field emission displays.

Uniform and well-crystallized calcium fluorapatite [Ca5(PO4)3F, FAP] microrods have been successfully synthesized by a facile one-step hydrothermal synthesis method using sodium citrate as the crystal modifier. X-ray diffraction (XRD), field emission-scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), photoluminescence (PL), photoluminescent excitation spectra (PLE) and decay studies were employed to characterize the samples. The electronic structure and orbital population of FAP were also determined by means of density functional theory calculations. Under ultraviolet irradiation, the FAP:Tb3+,Eu3+ samples exhibit a blue-light emission of the host matrix, as well as the typical green emission band of the Tb3+ ions, and a red-light emission of Eu3+. The highly intense red emission bands of the Eu3+ ions were attributed to the effective energy transfer from the Tb3+ to Eu3+ ions, which has been justified through the luminescence spectra and the fluorescence decay dynamics. The luminescence colors of FAP:Tb3+,Eu3+ microrods can be easily tuned by changing the concentration of Eu3+ ions. The results reveal that the combination of the self-activated luminescence and rare earth-doping emission in FAP:Tb3+,Eu3+ microrods could result in tunable emission in a large color gamut, which can be used as a potential candidate for white-light-emitting diodes and other display devices.

•Eu3+-doped cubic Ba3Y2WO9 phosphors were firstly synthesized by sol–gel method.•The luminescence excitation and emission spectra were discussed in details.•The crystallographic occupations of Eu3+ ions in cubic Ba3Y2WO9 were explored.Eu3+-doped cubic double perovskite Ba3Y2WO9 phosphors have been firstly successfully synthesized by sol–gel method. The prepared samples were characterized by X-ray diffraction (XRD) and field emission-scanning electron microscopy (FE-SEM). The luminescence excitation and emission spectra in the ultraviolet–visible (UV) region were used to investigate the luminescence properties of these phosphors. Then the site-selective excitation and emission spectroscopy along with luminescence decay have been investigated in the 5D0 → 7F0 region under a pulsed, tunable, narrowband dye laser at room temperature. In our study, the crystallographic occupations of Eu3+ ions were explored based on both spectroscopy and crystal structure of cubic Ba3Y2WO9:Eu3+. The multiple site structure of Eu3+ ions with highly disordered distributions in cubic Ba3Y2WO9 lattices was suggested. The results help us to understand the site assignments of rare earth ions doped in cubic Ba3Y2WO9.Graphical abstract

Cubic monodisperse BaCeF5 and BaCeF5:Tb3+ nanocrystals have been successfully synthesized by a citric acid assisted solvothermal method. The crystalline phase, size, morphology, and luminescence properties were characterized using powder X-ray diffraction (XRD), field emission-scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), photoluminescence (PL), photoluminescent excitation spectra (PLE) as well as dynamics decay. The results reveal that the Tb3+-doped BaCeF5 sample shows a strong green emission centered at 546 nm, corresponding to the 5D4→7F5 transition of Tb3+ due to an efficient energy transfer from Ce3+ to Tb3+. The decay lifetime of Ce3+ monotonically increases with increase of Tb3+ concentration. The critical energy transfer distance between Ce3+ and Tb3+ was also calculated by methods of concentration quenching and spectral overlapping. Experimental analysis and theoretical calculations reveal that the dipole–dipole interaction should be the dominant mechanism for the Ce3+–Tb3+ energy transfer.

Photoluminescence properties of Eu3+-doped GdAlO3 and LaAlO3 phosphors prepared by sol–gel method have been investigated by the site-selective laser spectroscopy along with the decay time measurements at room temperature. The site-selective excitation spectra showed one 7 F0 → 5D0 transition line in GdAlO3:Eu3+ and three 7 F0 → 5D0 transition lines in LaAlO3:Eu3+, indicating that there was only one crystallographic site for Eu3+ in GdAlO3 and three crystallographic sites for Eu3+ in LaAlO3. The result of LaAlO3 was not in agreement with its crystal structure. The stark energy levels for Eu3+ at different sites were characterized and discussed by site-selective emission spectra arose from 5D0 level of Eu3+.Highlights► The site-selective laser spectroscopy of Eu3+:RAlO3 (R = Gd, La) were investigated. ► One crystallographic site in Eu3+:GdAlO3 is assigned. ► Three crystallographic sites in Eu3+:LaAlO3 are assigned. ► Decay times of 5D0 → 7 F2 emission of Eu3+:RAlO3 (R = Gd, La) were also measured.

Novel monodisperse BaCeF5 and BaCeF5: Tb3+, Sm3+ nanocrystals have been successfully synthesized by a simple one-step solvothermal synthesis. Uniformly distributed nanocrystals with an octahedral morphology and particle size of 75–80 nm were observed. X-ray diffraction (XRD), field emission-scanning electron microscopy (FE-SEM), photoluminescence (PL), and decay studies were employed to characterize the samples. Under ultraviolet irradiation, the BaCeF5: Tb3+, Sm3+ samples exhibit the typical green emission band of the Tb3+ ions, as well as an orange-red and red emission bands of the Sm3+ ions in the presence of Ce3+ ions. The highly intense orange-red and red emission bands of the Sm3+ ions were attributed to the effective energy transfer from the Tb3+ to Sm3+ ions, which has been justified through the luminescence spectra and the fluorescence decay dynamics. The luminescence colors of BaCeF5: Tb3+, Sm3+ nanophosphors can be easily tuned by changing the concentration of Sm3+ ions. These results suggest that BaCeF5: Tb3+, Sm3+ nanocrystals can be explored for three-dimensional displays, back lighting, white light sources, and so on.

Uniform and well-crystallized calcium fluorapatite [Ca5(PO4)3F, FAP] microrods have been successfully synthesized by a facile one-step hydrothermal synthesis method using sodium citrate as the crystal modifier. X-ray diffraction (XRD), field emission-scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), photoluminescence (PL), photoluminescent excitation spectra (PLE) and decay studies were employed to characterize the samples. The electronic structure and orbital population of FAP were also determined by means of density functional theory calculations. Under ultraviolet irradiation, the FAP:Tb3+,Eu3+ samples exhibit a blue-light emission of the host matrix, as well as the typical green emission band of the Tb3+ ions, and a red-light emission of Eu3+. The highly intense red emission bands of the Eu3+ ions were attributed to the effective energy transfer from the Tb3+ to Eu3+ ions, which has been justified through the luminescence spectra and the fluorescence decay dynamics. The luminescence colors of FAP:Tb3+,Eu3+ microrods can be easily tuned by changing the concentration of Eu3+ ions. The results reveal that the combination of the self-activated luminescence and rare earth-doping emission in FAP:Tb3+,Eu3+ microrods could result in tunable emission in a large color gamut, which can be used as a potential candidate for white-light-emitting diodes and other display devices.

Uniform and well-crystallized YPO4·0.8H2O and YPO4·0.8H2O:Tb3+, Eu3+ nanocrystals have been successfully synthesized by a facile hydrothermal method using trisodium citrate (Cit3−) as a “shape modifier”. X-ray diffraction (XRD), field emission-scanning electron microscopy (FE-SEM), high-resolution transmission electron microscopy (HRTEM) and photoluminescence (PL) spectra were used to characterize the samples. It was found that the pH of the initial solution was responsible for determining the shape of the final products. In addition, the YPO4·0.8H2O samples prepared by Cit3−-assisted hydrothermal synthesis exhibited an intense and bright blue emission. Characterized with Fourier transform infrared (FT-IR) spectra and electron paramagnetic resonance (EPR) spectra, the carbon-related impurities induced by trisodium citrate (Cit3−) in the hydrothermal process were confirmed and confirmed that the paramagnetic defects relating to the luminescence properties existed in the luminescent YPO4·0.8H2O nanocrystals. More interestingly, the YPO4·0.8H2O:Tb3+, Eu3+ samples could be effectively excited with 380 nm and the luminescence colors of YPO4·0.8H2O:Tb3+, Eu3+ nanocrystals can be easily tuned by changing the concentration of Eu3+ ions due to an efficient energy transfer from Tb3+ to Eu3+. These results revealed that the combination of the defect luminescence and rare earth-doping emission in YPO4·0.8H2O:Tb3+, Eu3+ nanocrystals could result in tunable emission in a large color gamut, which may be potentially applied in fields such as solid state lighting and field emission displays.

Trivalent rare-earth (RE3+ = Eu3+, Tb3+) ion activated KLa(MoO4)2 microspheres have been synthesized at 180 °C via a facile hydrothermal route without using any templates, surfactant, or other organic additives. X-ray diffraction (XRD), field emission-scanning electron microscopy (FE-SEM), photoluminescence (PL), and photoluminescent excitation spectra (PLE) were employed to characterize the samples. It is found that the pH value in the initial solution is responsible for crystal phase, shape determination and emission intensity of final products. The possible formation mechanism for products with uniform spheres has been presented. Furthermore, a systematic study on the photoluminescence of RE3+ (RE3+ = Eu3+, Tb3+) doped KLa(MoO4)2 samples has been explored in order to obtain the multicolor tunable emission by varying the Tb3+/Eu3+ ratio. The tunable luminescence may be potentially applied in fields such as solid state lighting and field emission displays.