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A series of novel blue-emitting Ba 1-x Al 2 Si 3 O 4 N 4 : xEu2+ phosphors were successfully prepared by two-steps high temperature solid state reaction. The results of XRD and SEM showed that the two-steps method obtain less impurities than the traditional one-step method. The electronic band structure of BaAl 2 Si 3 O 4 N 4 (BASON) host was calculated as a direct band gap of 3.662eV by the DFT method. The PLE spectrum of B 1-x ASON: xEu2+ showed a wide band excitation in the wavelength range of 250–450 nm, which can be well matched with n-UV chips. Based on crystal structural and fluorescence lifetime analysis, three emission peaks were obtained by gaussian fitting to explain the asymmetry of Eu2+ emission in the BASON phosphor. The optimal doping concentration of Eu2+ was x = 0.04. According to calculated critical distance (3.24 Å) and a little overlap between PLE and PL spectra, the concentration quenching mechanism was confirmed as both of dipole-dipole interaction and radiation reabsorption. In addition, with the incorporation of Eu2+, the diffuse reflection spectrum of B 1-x ASON: xEu2+ presented a wide absorption peak in the range of 200–500 nm. The PL intensity of Ba 0.96-y Sr y Al 2 Si 3 O 4 N 4 : 0.04Eu2+ tended to rise first and then fall with the increase of Sr2+ concentration. Impressively, the relative emission intensity at 473K still maintained 95.7% compared with room temperature (293K), which indicated the excellent thermal stability of BASON phosphor. Finally, the density of state (DOS) of Ba 1-y Sr y Al 2 Si 3 O 4 N 4 (y = 0, 0.5, 1) were calculated and analyzed to explain the deterioration of thermal stability with the increase of Sr2+ substitution. • The pure-phase of Ba 1-x Al 2 Si 3 O 4 N 4 : xEu2+ phosphors were successfully prepared by two sintering steps with BaAlO 4 as precursor. • The PL intensity of BaAl 2 Si 3 O 4 N 4 : Eu2+ phosphors were significantly enhanced by substitution of Ba2+ with Sr2+ ions. • The BaAl 2 Si 3 O 4 N 4 : Eu2+ phosphors exhibit excellent thermal stability under 423K (97.9%). • The DOS of Ba 1-y Sr y Al 2 Si 3 O 4 N 4 (y = 0, 0.5, 1) were calculated and analyzed to explain the deterioration of thermal stability with the increase of Sr2+ substitution. [ABSTRACT FROM AUTHOR]

A series of spherical Er3+/Yb3+ doped Lu 2 O 3 and Lu 2 O 2 S phosphors co-doping with varying concentrations of Li+ (0, 1, 3, 5, and 7 mol%) were synthesized by homogeneous precipitation method followed by direct calcination or sulfurization. The crystal structure and morphology of the as-prepared phosphors were characterized by XRD, FTIR and SEM. Meanwhile, the upconversion (UC) luminescence spectra were recorded under 980 nm laser excitation at temperatures ranging from 303 to 573 K. The incorporation of lithium ions led to an enhancement of UC luminescence intensity by about 15 times at room temperature. The introduction of Li+ could also affect the temperature sensitivity of the samples. Furthermore, optical temperature sensing of the phosphors was achieved by analyzing the fluorescence intensity ratio (FIR) of thermally coupled levels (TCLs) and nonthermally coupled levels (non-TCLs). Impressively, utilizing the non-TCLs approach resulted in maximum S a values of 8.80 %K−1 and 11.06 %K−1 for the Er3+/Yb3+/5 % Li+ doped Lu 2 O 3 and Lu 2 O 2 S phosphors, leading to an approximately 17-fold and 23-fold increase compared to that of TCLs-based approach, respectively. The results of this work demonstrate the great potential of Er3+/Yb3+/Li+ doped Lu 2 O 3 and Lu 2 O 2 S phosphors for optical thermometers. • Monodisperse spherical Er3+/Yb3+/Li+ doped Lu 2 O 3 and Lu 2 O 2 S phosphors were successfully synthesized. • A simple, accurate, low cost and large-scale production method for rare earth doped Lu 2 O 3 and Lu 2 O 2 S phosphors was proposed. • The effects of Li+ on enhancement of upconversion luminescence and thermometric performance were investigated systematically. [ABSTRACT FROM AUTHOR]

The quenching of luminescence in Er3+/Yb3+ co-doped with Tm3+ presents a dilemma as it substantially diminishes thermometric performance. In this study, Y 2 O 2 S: Er3+/Yb3+/Tm3+ phosphors were synthesized using a homogeneous precipitation method combined with a sulfurization process. In addition, three sets of fluorescence intensity ratio (FIR) models were designed, which have self-calibration function. The effects of incorporation of Li+ or Li+/Ba2+ on the up-conversion luminescence (UCL) intensity and thermometric performance of the phosphors were systematically studied. The results show that the introduction of Li+ or Li+/Ba2+ co-doping leads to lattice distortion and the formation of oxygen ion vacancies in the lattice, which further accelerates the energy transfer process and mixes the charge transfer states, and ultimately dramatically improves the UCL and thermometric performance. The introduction of Li+ and Li+/Ba2+ co-doping enhanced the UCL of the materials by about 3.7 times and 5.6 times compared to Y 2 O 2 S: Er3+/Yb3+/Tm3+. When based on nonthermally coupled levels (NTCLs), the S r-max of Li+/Ba2+ co-doped sample is 0.080 K−1 at 573 K, which is 87 % higher than that based on TCLs. These findings not only provide a new avenue for improving the UCL and thermometric performance but also provide an accurate self-calibration FIR model over a wide temperature range. • Monodisperse spherical Y 2 O 2 S:Er3+/Yb3+/Tm3+ phosphors were successfully synthesized. • A simple, accurate, low cost and large-scale production method for rare earth doped Y 2 O 2 S phosphors was proposed. • The effects of Li+ and Li+/Ba2+ ions on enhancement of optical performance were investigated systematically. • Three sets of fluorescence intensity ratio models were designed and a self-calibration function was obtained. [ABSTRACT FROM AUTHOR]

The self-assembly mechanism of porous materials has always been a hot topic and a challenging issue in research. What factors induce the self-assembly process, and how is the temperature sensing performance related to it? Innovatively, in this paper, Gd 2 O 2 S:Er3+/Yb3+ phosphors with different morphologies were synthesized, and elucidated the formation mechanism of flower-like structures through relevant theorems, formulas, and experiments, proposing that polar molecules and dipole-dipole interactions guide the synergistic effect of van der Waals forces and hydrogen bonding, which ultimately induces the self-assembly of spherical structures into flower-like ones. In addition, four representative intermediates were selected to investigate their luminescence and temperature sensing properties. The results show that the flower-like sample can respond more effectively to changes in ambient temperature because of its rich pore structures, and thus exhibit better temperature sensing performance. In-depth research on the self-assembly mechanism of materials helps to predict and regulate their properties, and the unique characteristics of flower-like sample provide new ideas for material selection in the field of high-precision temperature measurement. • Successfully synthesized flower-like porous Gd 2 O 2 S:Er3+/Yb3+ phosphor for the first time. • The formation mechanism of self-assembly of spherical structures into flower-like structures was deeply investigated. • The up-conversion luminescence and thermometric performance of samples with different morphologies were studied. • The flower-like sample can respond more effectively to temperature changes, with its highest sensitivity reaching 0.089 K−1. [ABSTRACT FROM AUTHOR]

Abstract It was reported that the UC emission intensity can be improved by introducing a thermal field and this phenomenon is highly related to the Yb3+ ions. Herein, we verify the thermal-induced UC enhancement degree can be further increased by separating the Yb3+ ions in the core and shell to promote the population of the defect energy level and inhibit the back energy transfer from Ho3+ to Yb3+ ions. Graphical abstract Image 1 Highlights • Thermal-induced enhancement degree of Ho3+ decreases with increasing Ho3+ doping content. • High Yb3+ content benefit the population of the defect energy level. • High Yb3+ content also induce back energy transfer from Ho3+ to Yb3+ions. • The enhancement degree is further increased by constructing core-shell structure. [ABSTRACT FROM AUTHOR]

We report a detailed spectroscopic investigation of a series of fluorotellurite glasses with different Er 3+ ions concentration in system 50TeO 2 -27BaF 2 -9ZnF 2 -8YF 3 -3MgF 2 -3NaF-xErF 3 -1HoF 3 (x = 1,2,3 mol%). Intense 2 μm emission and 2.75 μm emission with high absorption and emission cross-section were observed under 980 nm LD pumping, and the maximum gain coefficient around 2750 nm was as high as 2.41 cm −1 , suggesting the prepared glasses are a competitive candidate for mid-infrared laser materials. Besides, it was found that the trend of 2 μm and 2.75 μm emission intensity varied with Er 3+ ions concentration was different. Energy transfer process was discussed subsequently to explain this phenomenon. Furthermore, we quantitatively investigate the energy transfer efficiency from Er 3+ : 4 I 13/2 level to Ho 3+ : 5 I 7 level. [ABSTRACT FROM AUTHOR]

A series of β-Sr 1.98- y Mg y SiO 4-1.5 x N x : 0.02Eu 2+ ( x = 0, 0.3, 0.6, 0.9, 1.2 and 4/3, 0 ≤ y ≤ 0.5, β-S(M)SON: Eu 2+ ) phosphors were synthesized by a conventional solid state reaction method. The coordination environments of Eu 2+ are modified effectively via the introduction of N 3- and Mg 2+ using different concentration, which is confirmed by XRD refinement results and PL spectra. Both fourier transform infrared (FT-IR) spectra and energy dispersive spectroscopy (EDS) analysis qualitatively confirm that the existence of N 3- . The crystal structures of β-Sr 2 SiO 4-1.5 x N x (β-SSON): Eu 2+ and β-Sr 2- y Mg y Si(O,N) 4 : Eu 2+ (β-SMSON, x = 4/3, y = 0.1) have been determined effectively. Rietveld refinement indicates that N 3- dopants most likely partly substitute O 2 2− site. With the increase of N content, the unit cell volume and partial Si O and Sr N bond lengths gradually decrease, which are coincided each other. With the introduction of N 3- , the emission of Eu(I) (∼465 nm) hardly change but that of Eu(II) (∼540 nm) splits into two emission bands as Eu(II) (∼540 nm) and Eu(II) ′ (∼616 nm). According to the analysis of XRD data, unit cell volume, FT-IR spectra, photoluminescence (PL) and reflectance spectra of β-SMSON: Eu 2+ , it can be concluded that the incorporation of Mg 2+ into the host leads to interstitial sites rather than substitutional ones. Mg 2+ doping couldn't change the dominant peak wavelengths (DPWs) of Eu(I), Eu(II) and Eu(II) ′ sites but only affects the PL intensity of title phosphors and could offset the nitridation effects. The concentration quenching mechanism and thermal activation energy of β-SSON: Eu 2+ phosphors are determined effectively. The β-S(M)SON: 0.02Eu 2+ phosphor have the feature that it can achieve color-tunable white light-emitting combined with blue light emitting diodes (LEDs) with single activator doped and single-phase host, which enables these materials to be enormous possibilities used in white light emitting diodes. [ABSTRACT FROM AUTHOR]

Quantum dot (QD)-embedded glass, which is a high-performance multifunctional optical material, has the combined advantages of excellent optical properties of QDs and easy processing of glass. In this study, an inorganic PbS QD embedded multicomponent glass, which produces variable emission at different ultraviolet (UV) excitation wavelengths, is synthesized. The samples are fabricated via a facile melt-quenching method and their structural, optical, photoluminescent, and morphological properties are discussed. The QD glass exhibits broad-band UV excitation in the range of 250–400 nm, and the full width at half maximum of the emission peaks of the QD glasses reaches 177.8 and 158.5 nm at room temperature under an excitation of 365 and 310 nm, respectively. Notably, white light emission with a high color rendering index is obtained under UV excitation at 350 and 365 nm by doping blue light emitting rare earth (RE) Tm3+ ions into the system. The doped samples exhibit excellent color stability and their CIE coordinates shift along the Planck blackbody locus with increasing temperature. Further, based on the differences in the luminescence mechanisms of the PbS QDs and Tm3+ ions, the application potential of the RE-doped PbS QD-embedded glasses in optical thermometry is discussed. The results demonstrate the application potential of these optically multifunctional inorganic QD glasses in the fields of optical conversion, anti-counterfeiting, white light illumination, and non-contact optical temperature measurement. [Display omitted] • PbS QDs were successfully prepared in an inorganic glass with broad-band emission. • Variable emission of PbS QDs glass at different UV excitation were obtained. • High CRI white light was obtained by combining the emission of PbS QDs with Tm ions. • A novel optical thermometer based on the inorganic PbS QDs glasses was revealed. [ABSTRACT FROM AUTHOR]

Highlights: [•] Ce3+/Mn2+ doped glass-ceramics containing β-Zn2SiO4 nano-crystals were prepared. [•] The glass-ceramics showed a tunable-color emission. [•] The resonant energy transfer from Ce3+ to Mn2+ via a dipole–quadrupole mechanism. [Copyright &y& Elsevier]

Abstract: KPb2Cl5:Mn2+ crystal with sizes of centimeters has been successfully grown by a modified Bridgman method. The electronic spectra of Mn2+ in the title compound have been measured at different temperatures and compared, revealing that the red emission observed at 10 and 77K in the spectral range from 500 to 800nm, which vanishes at room temperature, is associated with the radiation from Pb2+ ions with adjacent defects whereas the orange-red emission in the spectral range from 530 to 680nm can be undoubtedly attributed to the spin forbidden transition 4T1g (4G)→ 6A1g(6S) of Mn2+. The electronic excitation spectra are interpreted in a strong crystal field scheme with the use of the Tanabe–Sugano diagram. Good agreement with the experimental spectroscopic data is obtained with the use of crystal field splitting parameter 10Dq =7902cm−1, Racah parameters B =618cm−1, and C =3549cm−1. [Copyright &y& Elsevier]

Abstract: Eu2+/Sm3+ co-doped silicate glass was prepared by high temperature melting under reducing atmosphere and the Eu2+/Sm3+ co-doped SrSiO3 transparent glass-ceramics were obtained after heat-treatment. X-ray diffraction (XRD) and Raman spectra confirmed the formation of SrSiO3 nano-crystals in the glass matrix. The photoluminescence excitation (PLE) spectra and photoluminescence (PL) spectra of the samples were measured. A broad emission band from 400nm to 550nm due to the 4f65d1 →4f7 transitions of Eu2+ was observed, as well as several sharp emission peaks at 563nm, 600nm, 646nm and 713nm ascribed to the 4f→4f transitions of Sm3+. The luminescence properties of the glass ceramics with different molar ratio of Eu2+/Sm3+ were studied and the corresponding chromaticity coordinates were calculated. The ultraviolet light-emitting diode (UV-LED) excitable glass-ceramics emitting white light were obtained by tuning the relative emission intensity of Eu2+ and Sm3+. The results indicate that the Eu2+/Sm3+ co-doped SrSiO3 transparent glass-ceramics can be used as a potential matrix material for White LED under UV-LED excitation. [Copyright &y& Elsevier]

Optical thermometry technology plays a significant role in plenty of fields owing to its unrivaled properties such as sensitive, noncontact, reliable and so on. In this work, Er3+/Yb3+ codoped lanthanum titanate (La 2 Ti 2 O 7) microcrystals have been synthesized by solid state reaction for optical thermometry. This novel prepared material for thermometry is based on the fluorescence intensity ratio of thermally coupled levels from upconversion emission under 980 nm excitation. The sensitivity of thermometry is 5.7 × 10−3 K−1, and the input power density is only 8.3 mW/mm2. Furthermore, the result of repeatability test illustrates that the as-prepared microcrystals possess excellent stability at the temperature range from 333 to 553 K. Therefore, these demonstrated advantages of Er3+/Yb3+ codoped La 2 Ti 2 O 7 microcrystals make it a promising material in optical thermometry area. • The novel Er3+/Yb3+ codoped lanthanum titanate microcrystals are synthesized for optical thermometry. • A wide range of upconversion emission from ultraviolet to visible can be observed by the as-prepared sample. • The temperature sensitivity is enhanced under an extremely low pump power of 8.3 mW/mm2. • The sample reveals a wonderful repeatability performance within the temperature range from 300 to 553 K. [ABSTRACT FROM AUTHOR]