Co-doped Phosphors Research Articles

Variable luminnescence chromaticity and energy transfer in CaZnOS: Pr3+, Mn2+ by ultraviolet and blue excitations

Pr3+ and Mn2+ co-doped CaZnOS phosphors are prepared by high-temperature solid state reaction method and the photoluminescence property is investigated systematically. Under 283 ​nm ultraviolet and 447 ​nm blue light excitations, green emission from CaZnOS, Pr3+ and red emission from Mn2+ are obtained and the emission color is modulated from green to yellow and red by adjusting the ratio of Pr3+ to Mn2+ concentration. The photoluminescence process under 283 ​nm and 447 ​nm excitations are dependent on energy transfer from CaZnOS to Pr3+ and Mn2+, as well as energy transfer from Pr3+ to Mn2+. The energy transfer mechanism between Pr3+ and Mn2+ is confirmed to be dipole-quadrupole interaction. Particularly, under 447 ​nm blue excitation, CaZnOS: 1%Pr3+, 3%Mn2+ exhibits bright yellow emission with chromaticity coordinates of (0.372, 0.428) and quantum yields of 46.37%, implying a potential application in blue-chip excited white light emitting diodes (W-LEDs).

Size influence on optical thermometry of Er3+/Yb3+ Co-doped Y2O3 microspheres: From TCLs and Non-TCLs

Realization and optimization of enhanced/tunable optical luminescence properties is highly demanded for reliable and accurate temperature sensing. In this work, uniform monodisperse spherical Er3+/Yb3+ co-doped Y2O3 microcrystals of four different sizes have been synthesized via homogeneous precipitation by changing the reaction time, and the tuning of luminescence intensity/color was achieved by the controllable particles size. On this basis, by studying the particle size dependence of temperature sensing performance, we found that the behavior of absolute sensitivity (Sa) and relative sensitivity (Sr) have highly size dependence. Interestingly, when different FIR strategies were used (thermally coupled levels (TCLs) and nonthermally coupled levels (non-TCLs)), the sensitivity exhibits the opposite behavior. Importantly, when using the non-TCLs strategy, the maximum Sa value for the smallest phosphors was 1.084 K-1, leading to ∼246 times improvement compared to TCLs-based Sa. The ultrahigh Sa indicated that the Er3+/Yb3+ co-doped Y2O3 phosphors have potential in temperature detection, and the results are of guiding significance to studying the sensitivity of Y2O3 particle size-dependent temperature measurement.

Simultaneous influence of Mg2+ and Sc3+ co-doping on upconversion luminescence and optical thermometry in β-NaYF4: Yb3+/Ho3+ microphosphor

A series of xMg2+/ySc3+ co-doped β-NaYF4:0.2Yb3+/0.02Ho3+ (x = y = 0 −0.2) upconversion (UC) green phosphors are synthesized using EDTA-assisted hydrothermal method. The structure, morphology and elemental compositions are investigated in detail using different experimental techniques. The lengthwise suppression of crystal due to co-doping is associated to the kinetics involved in the crystal growth in presence of Mg2+/Sc3+. The effect of Mg2+/Sc3+ co-doping on the UC green emission of β-NaYF4:0.2Yb3+/0.02Ho3+ microphosphors is studied and about 31-fold enhancement in the green emission (5F4,5S2→5I8) is observed for the 0.08Mg2+/0.12Sc3+ co-doped phosphor. The downconversion properties of the phosphors is also discussed to showcase the dual mode luminescence. The temperature sensing performance is investigated using luminescence intensity ratio (LIR) technique for non-thermally coupled levels (5F5/5F4,5S2) of Ho3+ ions and maximum relative sensitivity of 0.258% K−1 at 374 K is obtained for the optimized phosphor. The microphosphor can be sustained at high temperature as the UC emission intensity retains about 65% and 36% at 423 K and 574 K. From chromaticity diagram, the maximum color purity of 91.37% is obtained for 0.08Mg2+/0.12Sc3+ doping concentration. The estimated thermal parameters and color purity of Mg2+/Sc3+ co-doped β-NaYF4:0.2Yb3+/0.02Ho3+ UC phosphors suggest their applicability in fabricating temperature sensors and LEDs.

Energy transfer induced color tunable photoluminescence in Tb3+/Sm3+ co-doped Y2O3 nano-phosphor for warm white LEDs

In this work, the Tb3+/Sm3+ doped and co-doped Y2O3 nano-phosphors have been prepared by solution combustion method. The structural and morphological analyses of Y2O3 nano-phosphors confirm its nano-crystalline structure. The EDS spectra reveal the evidence of Y, Sm, Tb and O elements in the co-doped phosphor. The excitation spectrum of the Tb3+/Sm3+ co-doped nano-phosphor contains the excitation bands due to Tb3+ and Sm3+ ions. The Tb3+ doped nano-phosphor gives intense green (541 nm) and slightly weak blue (483 nm) emissions upon 292 nm excitation. The critical distance and PL intensity per activator ion were calculated to identify the factor responsible for quenching the PL intensity. The PL intensity of green and blue emission bands decreases regularly via doping of Sm3+ ion. This occurs due to energy transfer from Tb3+ to Sm3+ ions. The energy transfer leads to improve the PL intensity of the orange red emission band of Sm3+ ion. The energy transfer has been verified by the lifetime measurements and the energy transfer efficiency is found to increase via doping of Sm3+ ion. The CIE diagrams show wide color tunability from the greenish yellow to reddish orange regions and the color purity of Tb3+ doped nano-phosphor also changes accordingly via Sm3+ doping. The CCT analysis of Tb3+/Sm3+ co-doped nano-phosphors indicates a warm nature of the emitted light. Therefore, the Tb3+/Sm3+ co-doped Y2O3 nano-phosphor may be applied in the field of display devices, color tunable devices and warm white LEDs.

Multi behaviors of Dy3+ for improving the luminescence properties of Pr3+-activated Sr3Al2O6 orange-reddish phosphors

Pr3+/Dy3+ co-doped Sr3Al2O6 phosphors were synthesized by a solid-state reaction. The powder X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), photoluminescence (PL), and thermoluminescence (TL) were analyzed to investigate the luminescence and structure properties of the samples. The introduction of Dy3+ ions as multi behaviors significantly improve the luminescence properties of the phosphors. Dy3+ ions also behave as an emission center, showing the strong emission peaks at 617 nm and 645 nm, and work together with the activator of Pr3+ to responsible for the red color of the phosphors. The dopant of Dy3+ can significantly increase the trap concentrations with a suitable trap depth of 0.79 eV to extend the afterglow time of the materials. There exists some energy level overlaps among some excitation peaks of Dy3+ and some emission peaks of Pr3+, showing that Dy3+ ions still behave as sensitizers to improve the luminescence properties of the materials. Based on the energy band theory and defect theory, the luminescence mechanism of Pr3+/Dy3+ co-doped Sr3Al2O6 phosphors was proposed.

Analysis of influencing factors and changing laws on fluorescence lifetime of Er3+, Yb3+ Co-doped Gd2O2S phosphor

Although rare earth up-conversion luminescent materials have become a research topic for many researchers because of its excellent luminescent properties, the variation of its fluorescence lifetime is still a problem worth discussing. The Er3+, Yb3+ co-doped Gd2O2S phosphor prepared by the high temperature solid state method was used to study the change law of fluorescence lifetime. The effects of different calcining temperature (1000 °C–1175 °C), calcining time (3.0 h–5.5 h), concentration of Er3+ (0.1 mol% – 30 mol%) and the doping ratio of Er3+:Yb3+ (1:1–1:7) on the properties and fluorescence lifetime of the synthesized Er3+, Yb3+ co-doped Gd2O2S phosphor were investigated, and the orthogonal experiments were used to optimize the factors. The structure and morphology evolution of the Gd2O2S: Er3+, Yb3+ phosphor was systematically studied by X-ray powder diffraction (XRD). The fluorescence properties of Gd2O2S: Er3+, Yb3+ phosphor were studied from the aspects of emission spectrum and fluorescence lifetime. This work would provide a new perspective for applying fluorescence lifetime analysis of energy transfer in up-conversion luminescence materials.

Enhanced red-UC luminescence through Ce3+ co-doping in NaBiF4:Yb3+/Ho3+(Er3+)/Ce3+ phosphors prepared by ultrafast coprecipitation approach

Series of Yb3+/Ho3+(Er3+)/Ce3+ co-doped NaBiF4 phosphors were synthesized through an ultrafast co-precipitation reaction technique at room temperature. The effect of the Ce3+ ions on the crystal structure and upconversion (UC) luminescence properties of the studied samples were investigated in detail. FTIR and XPS demonstrated the pre-formation of NaBiF4 and the introduction of Yb3+, Ho3+, Er3+ and Ce3+ all as dopants in the host materials. Under 980 nm excitation, NaBiF4:Yb3+,Ho3+(Er3+),Ce3+performed the characteristic emission of the activator ion, and the introduction of Ce3+ did not change the emission wavelengths, only the relative intensities. Due to partial good energy overlap when 2F7/2 Ce3+ manifold is populated, raising Ce3+ ions concentration enhanced the red UC emission versus green UC emission but also lead to significant decrease in the average lifetimes of all monitored emissions for Ho3+ and Er3+. These lifetime decreases are explained by the energy loss in non-radiative pathways after the introduction of Ce3+. In addition, the green to yellow color emission change through addition of Ce3+ was explored in NaBiF4: Yb3+,Ho3+,Ce3+ to propose a novel application in two-level anti-counterfeiting.

Investigation on effect of Ca2+ ions in SrLa2O4:Dy3+ phosphors for solid state lighting application

White light emitting SrLa2−xO4:Dy3+/0.05 Ca2+phosphors are prepared by solid state reaction technique at 1200◦C.X-ray diffraction method interprets the phase structure of the material while the luminescence properties of the co-doped SrLa2O4 phosphors and energy transfer mechanism are scrutinized by photoluminescence spectra analysis. Two main emission peaks are attributed at 484 nm and 571 nm due to the Dy3+ions under 324 nm excitation wavelength. The resultant output is in consonance with the synthesis white-light emitting phosphors can be obtained from the single host material at x = 0.06 doping concentration Dy3+ ions. The phosphors reveal a strong absorption band obtained in UV region and the observed white-light emission with chromaticity co-ordinates read x = 0.326, y = 0.362. The inference illustrates the synthesis material prospective candidate for white LED applications.

Development of novel Eu2+ and Li+ Co-doped cyan-emitting aluminosilicate phosphors

The cyan emission band contains blue and green light regions, which can simplify the fabrication process of white light-emitting diodes and help promote the development of solid-state lighting. In this paper, a series of Eu2+ singly doped and Eu2+ and Li+ co-doped cyan light-emitting KAlSiO4:x Eu2+, y Li + materials were synthesized using the high temperature solid-state method. It was found that the incorporation of 10% Li + could increase the emission intensity of the KAlSiO4:0.02Eu2+ sample by up to a factor of ∼3. This also shifted the emission color of the sample from blue-cyan (472 nm) to cyan (485 nm), and the quantum yield was increased from 71.5% to 93.3%. When the temperature is increased to 150 °C, the peak emission intensity was increased from 75.9% to 92.7% of that at room temperature. DFT calculations were used to demonstrate that the KAlSiO4 phosphor host possesses a wide bandgap of 4.86 eV and the experimentally-determined optical bandgap of the phosphor was 5.6 eV. The phosphor was combined with a commercial red phosphor, and these together were used as the emitting components in a white LED package. The characteristics of the white LED when using two representative samples of the phosphor (KAlSiO4: 0.02Eu2+ and KAlSiO4: 0.02Eu2+, 0.1Li+) were examined; these white LEDs had color rendering indices of 82 and 95, and color temperatures of 5656 K and 4126 K respectively. This work demonstrates the significant potential that KAlSiO4:0.02 Eu2+, 0.1 Li+ phosphors have in the field of LED lighting.

Physicochemical properties of Li3Ba2La3(MoO4)8:Eu,Tb red-emitting phosphor for solid state white lamps

In this work, combustion synthesis was used for the first time to fabricate a phosphor material with red emission for applications in solid-state white-light lamps. We synthesized a material with emission wavelength at λem = 617 nm, excited under long UV-blue wavelength based on Eu3+, Tb3+-activated molybdates Li3Ba2(La1–x–yEuxTby)3(MoO4)8 with 0 ≤ x ≤ 1 and 0 ≤ y ≤ 1. A series of powder samples were produced by the combustion method and post-annealed at 800 °C in air. The crystalline phase formation was investigated by X-ray diffraction, which reveals the monoclinic C2/c (15) space group. It is observed that crystalline structure and morphology are preserved when the host lattice is doped with Eu3+ or Tb3+ single ions and co-doped with both ions at different doping concentrations. A detailed characterization by scanning electron microscopy (SEM) and transmission electron microscopy (TEM) shows a similar morphology in all samples: rather large (1–7 μm) agglomerate particles with irregular shapes and surrounded by smaller nanoparticles of 50 nm in size. UV–visible absorption spectra confirm the presence of Eu3+ and Tb3+ ions. The luminescent properties of the obtained phosphors were studied in detail. Cathodoluminescence measurements indicate that the best emission intensity is for Eu3+:Tb3+ doping ratios of 80:0, 90:0 and 20:80. On the other hand, samples with 80:0, 60:40, and 20:80 doping ratios show the highest intensity in a detailed photoluminescence analysis and they exhibit the highest quantum yield values. A complete and efficient energy transfer from the sensitizer Tb3+ to the activator Eu3+ is observed in all co-doped phosphors post-annealed at 800 °C for 4 h. Thus, the Li3Ba2La3(MoO4)8:Eu3+,Tb3+ materials fabricated by combustion synthesis are excellent phosphors for being applied as red-emitting component in solid-state white-light lamps due to an improved color rendering index (CRI) that can be obtained under long UV-blue excitation wavelengths.

Linear and non-linear photoluminescence studies of Ho3+/Yb3+ co-doped titanate phosphors for photonic applications

This work presents the morphological and photoluminescence (PL) studies of the single ion Ho3+ doped and Ho3+/Yb3+ co-doped Ba3−x-yMoTiO8:xHo3+/yYb3+ phosphors synthesized by conventional solid-state reaction method. Phase confirmation of all the as-prepared samples was done by X-Ray Diffraction (XRD) patterns. The morphological behavior and vibrational frequency bands were studied by Scanning Electron Microscope (SEM) and Fourier Transform Infrared (FT-IR) techniques respectively. Diffuse Reflectance Spectra (DRS) has been recorded for the singly doped and co-doped samples to find out the optical bandgap. The linear and non-linear emission spectral studies under 448 and 980 nm excitation wavelengths respectively showed three bands in the green, red, and blue regions. A relatively more intense band observed in the green region under 980 nm excitation shows promising usage of the titled phosphor for non-linear applications. A plot drawn between non-linear luminescence emission intensity Vs pump power reveals the information pertaining to the number of photons involved in the process. In addition, Commission Internationale de I′Eclairage (CIE) coordinates calculated from the emission spectral features lie in the green region. All the studies show the broad application of the as-prepared phosphors in linear and non-linear luminescence process-based green emitting diodes, display devices, security inks, phototherapy, and solid-state lighting (SSL) applications.

Intense green photoluminescence and upconversion-based intrinsic optical bistability in Ho3+/Yb3+ codoped CaSc2O4 and upconversion in Ho3+/Yb3+ codoped CaY2O4 phosphors

The present study details the downshifting, frequency upconversion and intrinsic optical bistability in CaSc2O4:Ho3+/Yb3+ and upconversion in CaY2O4:Ho3+/Yb3+ phosphors synthesized by a complex-based precursor solution method. The X-ray powder diffraction confirms the formation of highly crystalline phosphors with pure orthorhombic phase. Fourier transform infrared studies of synthesized phosphors show vibrational bands due to the presence of Ca–O, Sc–O and Y–O groups. The diffuse reflectance spectra show a number of bands in the UV–vis–NIR regions due to presence of Ho3+ and Yb3+ ions. The values of optical band gap (Eg) are found to be 5.69 eV and 5.58 eV for the Ho3+/Yb3+ codoped CaSc2O4 and CaY2O4 phosphors, respectively. The Ho3+/Yb3+ codoped CaSc2O4 phosphors display intense green downshifting emission upon 454 nm excitations. The lifetime of green luminescence of CaSc2O4:Ho3+/Yb3+ phosphors with varied Yb3+ concentrations have also been measured. The decay curves show a non-exponential nature fitted to the Inokuti-Hirayama model and the energy transfer microscopic parameters have been also calculated. The Ho3+/Yb3+ co-doped CaSc2O4 and CaY2O4 phosphors display intense green alongwith weak blue, red, and near-infrared upconversion (UC) emissions upon 980 nm excitations. The spectral color purity (Sgr) of CaSc2O4:Ho3+(1%)/Yb3+(5%) phosphor is calculated to be 0.78. Importantly, the variation of pump power generates intrinsic optical bistability (IOB) in the CaSc2O4:Ho3+(1%)/Yb3+(5%) phosphor for the green emission, which is not observed in the CaY2O4:Ho3+(1%)/Yb3+(5%) phosphor. Therefore, the Ho3+/Yb3+ co-doped CaSc2O4 phosphor could potentially be used in UC-based devices, optical memory devices, optical gates, optical transistors and switching devices for optical communications.

A novel Ba2SrWO6:Mn4+/Dy3+ red phosphors for warm WLED applications

A novel non-rare-earth red-emitting phosphor of Ba2SrWO6:Mn4+ with a double-perovskite structure was synthesized via a solid-state reaction method at high temperatures, and the mechanism of structural formation was systematically investigated. Moreover, Dy3+co-dopant ions were exploited to develop a white-light phosphor of Ba2SrWO6:Mn4+/Dy3+. Excitation spectra of Ba2SrWO6:Mn4+ and Ba2SrWO6:Mn4+/Dy3+ were both in a wavelength range of 250–550 nm. Under 325 nm excitation, the Ba2SrWO6:Mn4+ phosphors showed a red emission with a peak at 693 nm because of the 2E → 4A2 transition of Mn4+ ions. The Mn4+ ion concentration in the Ba2SrWO6:Mn4+ phosphors was optimized at 0.6 mol%, and the corresponding CIE (Commission International de I’Edairage) chromaticity coordinate was determined at about (0.7238, 0.2762), locating in the deep-red-light region. Meanwhile, the white-light Ba2SrWO6:Mn4+/Dy3+ phosphors displayed a wide emission band, including a blue emission at 492 nm (attributed to 4F9/2 → 6H15/2), a yellow emission at 582 nm (owing to 4F9/2 → 6H13/2), and the red emission at 693 nm. By varying the Dy3+ ion concentration, the emission color of the co-doped phosphors can be tuned from white light (0.3365, 0.3493) to warm white-light (0.4263, 0.3778), qualifying the phosphorous materials as a potential candidate for white-light- or warm white-light-emitting diode applications.

Preparation and near-white luminescence properties of Bi3+ doped and Bi3+/Eu3+ co-doped germanate phosphor powder

The Bi3+ doped and the Bi3+/Eu3+ co-doped germanate phosphor powders were synthesized by high-temperature solid-state reaction and their luminescence properties were investigated. The XRD analysis results show that the crystalline phase of all samples is the tetragonal phase of BaGeO3. The Bi3+ doped BaGeO3 phosphors exhibited an intense near-white light emission and the wavelength of the luminescence center was located at 466 nm. The Bi3+ doped BaGeO3 phosphors can be efficiently excited by the incident light of 260–430 nm. The tunability of the emission color can be achieved by changing the Bi3+ ion doping concentration and the high-temperature sintering time. The Bi3+/Eu3+ co-doped BaGeO3 phosphors exhibited an intense red emission and the wavelength of the luminescence center was located from 466 to 705 nm. The Bi3+/ Eu3+ co-doped BaGeO3 phosphors can be efficiently excited by the incident light of 312–532 nm. The emission color tunability can be obtained by changing the Eu3+ ions doping concentration and the wavelength of excitation. The visible region emission characteristics of BaGeO3:Bi3+, Bi3+/Eu3+ indicate that it can potentially be used as a new efficient near-white luminescent material.

Intense red up-conversion luminescence and temperature sensing property of Yb3+/Er3+ co-doped BaGd2O4 phosphors

In this study, intense red and extremely weak green up-conversion (UC) luminescence was obtained in BaGd2O4: x mol% Yb3+/y mol% Er3+ phosphors under the excitations of 980 nm and 1550 nm. The corresponding maximum integrated intensity ratios of the red to green UC emissions are 50.3 and 158.7, respectively. The UC luminescence mechanisms upon different excitations were discussed. It was confirmed that two-photon and three-photon processes were responsible for both the red and green UC emissions excited at 980 nm and 1550 nm, respectively. The energy transfer efficiency from Er3+ to Yb3+ was calculated according to the fluorescence lifetime measurement under 1550 nm excitation. Temperature sensing based upon the thermally coupled energy levels 2H11/2/4S3/2 as well as thermally coupled Stark sublevels of 4F9/2 level of Er3+ was investigated under the excitation of 980 nm. The maximum absolute sensitivities were respectively obtained to be 0.42% K−1 at 573 K and 0.18% K−1 at 298 K. Our results indicated that BaGd2O4: Yb3+/Er3+ phosphors might be a kind of promising red UC phosphors with optical temperature measurement function.

Synthesis and photoluminescence performance of single-component Ca3YAl3B4O15:Dy3+, Eu3+ white-emitting phosphor for white light-emitting diodes

A single-component Ca3YAl3B4O15 (CYAB):Dy3+, Eu3+ phosphor was synthesized by the traditional high temperature solid-phase method, Dy3+ and Eu3+ were codoped in the structure to obtain a warm white emission. The results of XRD and EDS revealed that all samples had the standard Ca3YAl3B4O15 structure, and no impurity phase appeared with codoping. The emission of Dy3+ in CYAB consisted of both main peaks at 476 nm and 570 nm, with which a white emission could be observed. Furthermore, a characteristic emission peak of Eu3+ appeared at 617 nm in Dy3+/Eu3+-codoped samples to supplement red component for the white emission of Dy3+, due to the energy transfer effect between Dy3+ and Eu3+. With the amount of Eu3+ raised, the correlated colour temperature of CYAB:Dy3+, Eu3+ phosphor obviously decreased, and a warm white light was successfully realized from the manufactured w-LEDs. Therefore, all results indicated that the single-component Dy3+/Eu3+ codoped CYAB white-emitting phosphor had a potential application in ultraviolet excited w-LEDs.

Ratiometric optical thermometer with high-sensitive temperature sensing based on tunable luminescence of Ce3+-Eu2+ in KSr4B3O9 phosphors

It is a challenge to develop a new type of non-contact temperature sensor and the related materials with the advantages of high detection sensitivity, spatial resolution, non-invasive and fast response. In this work, a moderate solid-state method was utilized to prepare a novel Ce3+/Eu2+ co-doped KSr4B3O9 phosphor for efficient dual-emission temperature-sensing application. According to the different activation energy and the energy transfer process from Ce3+ to Eu2+, two non-overlapping emission bands with respectively distinctive temperature responses were realized. By using the significant difference in the fluorescence intensity ratio between Eu2+ and Ce3+, a strong shift of the CIE coordinate from (0.3701, 0.4311) at 293 K to (0.2623, 0.2465) at 443 K could be read out. Meanwhile, the maximum absolute (Sa) and relative sensitivities (Sr) were fitted to be 0.0118 and 2.25 % K−1 with a large chromaticity shift from 293 to 443 K (ΔE = 0.1652). The configuration coordinate diagram in KSr4B3O9 was adopted to explain the temperature quenching mechanism in detail. The outstanding temperature-sensing characteristic indicates that KSr4B3O9: 1.75 %Ce3+/1.75 %Eu2+ phosphor has the potential to be applied in a thermometric probe.

External-field-dependent tunable emissions of Er3+-In3+ Co-doped Cs2AgBiCl6 for applications in anti-counterfeiting

Anti-counterfeiting materials play an irreplaceable role in information security and reducing national and enterprise losses, while the fluorescent anti-counterfeiting materials are widely used because of their feasible and flexible designs, visibility, easy identification and difficulty in cracking. For enhancing the security of fluorescent anti-counterfeiting materials, it is a popular choice to increase the modulus throung combining the up-conversion (UC) and down-conversion (DC) together with dynamic luminescence in one. Herein, Er3+ and In3+ co-doped Cs2AgBiCl6 phosphors with UC and DC emissions were successfully developed, in which Er3+ ions are responsible for the green UC emission under the excitation of 980 or 1550 nm laser while In3+ take the responsibility of enhancing yellow DC emission with 365 nm near ultraviolet light excitation. Furthermore, the DC luminescence color gradually changes to white from yellow as the ambient temperature increases from room temperature to 490 K. The potential application of the present samples in the field of anti-counterfeiting was evaluated by designing different patterns with the help of screen printing technology, which implied that the present sample provided a feasible and facilitated way to address the counterfeit issues.

Low-temperature sintered Pr3+/Er3+ codoped Bi2Mo2O9 microcrystals for multimode optical thermometry and anti-counterfeiting

Lanthanide-doped oxide materials generally require high sintering temperatures for optical applications such as temperature sensing and anti-counterfeiting. In this work, the highly crystalline 1%Pr3+/1%Er3+ co-doped Bi2Mo2O9 phosphor is reported with a low sintering temperature of 923 K. Pr3+ in the Bi2Mo2O9 host has a narrow emission band of 3P0–3H6 transition at 624 nm due to the suppressed broadening of electronic transitions in the homogeneous crystal field. Multimode temperature sensing is realized based on the upconversion and downshifting emissions as well as the luminescence lifetimes of the as-prepared phosphor. The temperature sensing based on the downshifting emission bands of this phosphor at 530 and 624 nm achieves the maximum absolute and relative sensitivities of 0.693 K−1 at 568 K and 1.88% K−1 at 483 K, respectively. For anti-counterfeiting applications, this phosphor can display bright yellow fluorescence at the liquid nitrogen cooling temperature, rather than white or pale colors. The white-color emission of this phosphor excited by 254 nm can also be used for lighting. The lanthanide-doped Bi2Mo2O9 can achieve favorable luminescence performance at much lower sintering temperature than most oxide phosphors, and is not only stable but also has the potential for in-situ sintering on materials that are not resistant to high temperature.

Enhancement of the NIR Emission of Cr3+-Yb3+ Co-doped La3GaGe5O16 Phosphors by Doping Nd3+ Ions via Efficient Energy Transfer for NIR Spectroscopy Regulation.

The efficient energy transfer in La3GaGe5O16:Cr3+, Yb3+/Nd3+ and La3GaGe5O16:Cr3+, Yb3+, Nd3+ was investigated in detail. In this phosphor, Cr3+ acts as the energy absorber (250-700 nm) to sensitize Yb3+/Nd3+ in La3GaGe5O16. Under excitation at 418 nm, La3GaGe5O16:Cr3+, Yb3+ phosphors exhibited a broad emission band in the near-infrared (NIR) region located at 976 nm (La3GaGe5O16:Cr3+, Nd3+ at 1056 nm), which was attributed to the 2F5/2-2F7/2 transition of the Yb3+ ions (2F3/2 → 4I11/2 transition of Nd3+). Moreover, a Nd3+ ion was introduced into La3GaGe5O16:Cr3+, Yb3+. The analysis of excitation spectra and decay time proves that Nd3+ acts as a bridging ion in the system. This can be used as a new strategy to enhance the energy transfer in Cr3+, Yb3+ co-doped phosphors, and these phosphors have potential applications in NIR spectroscopy regulation.