Green UC Research Articles

Enhanced green up-conversion in Eu3+/Ho3+/Yb3+ tri-doped Na5Y9F32 single crystals excited by 980 nm

Eu3+/Ho3+/Yb3+ tri-doped Na5Y9F32 single crystals were synthesized by a Bridgman method. The up-conversion emissions centered at 544 and 658 nm, corresponding to the 5F4/5S2→5I8 and 5F5→5I8 transitions, were observed under the excitation of 980 nm LD. The effects of Eu3+ ion on the up-conversion emission were investigated. The green up-conversion emission at 544 nm initially increased and then decreased as the Eu3+ concentration increasing from 0 to 2.1 mol%. The intensity at 544 nm reached to maximum when the doped concentration of Eu3+ was ∼0.6 mol%. The energy transfer mechanism analysis suggests that the cross-relaxation process between Ho3+ and Eu3+ ions was responsible for the change of green UC emission. Furthermore, its external quantum efficiency (EQE) approached to 1.3% is obtained for Na5Y9F32: 0.6 mol %Eu3+/0.6 mol% Ho3+/3 mol% Yb3+ under 1 W/cm2 980 nm excitation which can be applied in UC related optical devices. The nearly quadratic dependence of pump power on UC emissions at 544, 589, 610 and 658 nm indicates that one visible photon was generated with the absorption of two NIR photons.

High-purity green emission in Yb3+/Ho3+ Co-doped BaIn6Y2O13 up-conversion phosphor

Yb3+-Ho3+ pairs doped BaIn6Y2O13 (BIY) phosphors were successfully prepared through sol-gel process, and the crystal structure and optical properties were investigated in detail. As-prepared samples exhibited strong green and weak red emission peaked at 549 nm and 652 nm originated from Ho3+ transitions of 5S2, 5F4 → 5I8 and 5F5 → 5I8 with 980 nm excitation, respectively. The dopant contents, pumping power and pulse width of excitation laser dependent up-conversion luminescence (UCL) spectra of samples were modulated to acquire the intense and high-purity green emissions. Moreover, possible dynamic UCL process from non-steady-state to steady-state between Yb3+ and Ho3+ was schematically proposed in detail. These results indicate that BaIn6Y2O13: Yb3+/Ho3+ phosphors with strong and pure green UC emissions are potential candidates in display and lighting technology.

Tuning up-conversion luminescence in Er3+-doped glass ceramic by phase-shaped femtosecond laser field with optimal feedback control

Tuning the color output of rare-earth ion doped luminescent nanomaterials has important scientific significance for further extending applications in color displays, laser sources, optoelectronic devices, and biolabeling. In previous studies, pre-designed phase modulation of the femtosecond laser field has been proven to be effective in tuning the luminescence of doped rare-earth ions. Owing to the complex light–matter interaction in the actual experiment, the dynamic range and optimal efficiency for color tuning cannot be determined with the pre-designed phase modulation. This article shares the development of an adaptive femtosecond pulse shaping method based on a genetic algorithm, and its use to manipulate the green and red luminescence tuning in an Er3+-doped glass ceramic under 800-nm femtosecond laser field excitation for the first time. Experimental results show that the intensity ratio of the green and red UC luminescence of the doped Er3+ ions can be either increased or decreased conveniently by the phase-shaped femtosecond laser field with an optimal feedback control. The physical control mechanisms for the color tuning are also explained in detail. This article demonstrates the potential applications of the adaptive femtosecond pulse shaping technique in controlling the color output of doped rare-earth ions.

White light upconversion emission and color tunability in Er3+/Tm3+/Yb3+ tri-doped YNbO4 phosphor

Er3+/Tm3+/Yb3+ tri-doped YNO phosphors were obtained by the solid-state reaction method. X-ray diffraction, Raman spectroscopy, and FE-SEM were employed for characterization of the materials, and no significant structural changes have been noticed. The materials exhibited red, green and blue (RGB) upconversion emissions under 980 nm excitation. The increase of the Tm3+ concentration reduced the blue and green UC emissions due to possible Tm3+-Tm3+ and Er3+-Tm3+ energy transfer processes, respectively. White UC emission with CIE color coordinates equal to x = 0.31 and y = 0.35 has been obtained in the YNO:0.5%Er3+2.0%Tm3+20%Yb3+ composition under 64.5 mW/cm2. The tri-doped systems presented color tunability behavior indicating that multicolor, such as white light, can be easily achieved by adjusting of the Tm3+ and Yb3+ contents.

Upconversion photon quantification of Ho3+ in highly transparent fluorotellurite glasses

Multi-photon-excited green, red and oxblood UC emissions have been quantified in highly transparent Ho3+/Yb3+ doped fluorotellurite (BALMT) glasses under the excitation of 977 nm laser. The net powers of green, red and oxblood emissions are determined to be 88.1, 103.8 and 66.1 μW in 0.196% Ho2O3 and 0.752% Yb2O3 co-doping case under the excitation power of 870 mW, and the net emission photon numbers are identified to be 242.7 × 1012, 342.8 × 1012 and 250.8 × 1012 cps. The quantum yields (QYs) and luminous fluxes for visible UC emissions of Ho3+ are identified as a positive dependency with pumping powers, and when the excitation power density increase to 110.8 W/mm2, the QY values for 550 nm green, 650 nm red and 753 nm oxblood UC emissions are up to 0.63 × 10−4, 0.90 × 10−4 and 0.65 × 10−4, respectively. The values of QY in Ho3+ doped BALMT glass are one order of magnitude larger than that in NMAG glasses. The macroscopic quantization for UC photon generation from Ho3+ in low-phonon fluorotellurite glasses provides a reliable reference for developing compact high-power-density illuminant for remote sensing, radar detection and medical diagnosis.

Zirconia based Ho3+–Yb3+ codoped upconverting nanophosphors for green light emitting devices applications

Photoluminescence study of the Ho3+–Yb3+ codoped ZrO, AlZrO and YZrO nanophosphors, synthesized by chemical co-precipitation method, upon excitation at 450 and 980 nm radiations have been performed. An improvement of about ∼4.5 times in the downconversion emission intensity of green band corresponding to the 5F4, 5S2 → 5I8 transition for codoped YZrO nanophosphors compared to ZrO codoped nanophosphors has been observed. On varying the pump power density upon 980 nm excitation the colour tunability in the codoped YZrO nanophosphors has been observed. UC emission intensity of the green band arising from the Ho3+ ion in the codoped YZrO nanophosphors is enhanced about ∼22 times compared to that of the codoped ZrO nanophosphors. The absorption and UC emission study for the codoped YZrO nanophosphors dispersed in different biologically compatible solvents viz. water, methanol, ethanol and dimethyl sulfoxide (DMSO) has been performed. The green UC emission intensity of about ∼1.3 and ∼1.7 times for the efficient codoped YZrO nanophosphors dispersed in methanol compared to that dispersed in water and DMSO respectively has been observed. The absorption spectra of an efficient upconverting YZrO nanophosphors dispersed in methanol exhibit no change with the passage of time.

An upconversion luminescence and temperature sensor based on Yb3+/Er3+ co-doped GdSr2AlO5.

GdSr2AlO5:Yb3+/Er3+ micro-particles were synthesized by a simple solid state method. The structure, morphology, size and upconversion luminescence features have been characterized. These results indicated that GdSr2AlO5 has a contracted tetragonal cell and has irregular block shaped particles with sizes of about 5 μm. During upconversion, green (2H11/2, 4S3/2 → 4I15/2) (527 nm, 549 nm) and red (4F9/2 → 4I15/2) (665 nm) emissions had been observed, both of which occurred via a two-photon population process. In addition, green UC emission characteristics were studied, and it was found that its temperature ranged from 293 K to 473 K and the sensitivity was 0.0054 K−1 at 473 K. This indicated that GdSr2AlO5:Yb3+/Er3+ micro-particles may have potential application in high temperature environments for safety signs.

Electric and optical properties of Er3+- and Er3+/Yb3+-modified PSN-PMN-PT crystals

PSN-PMN-PT, Er3+-, and Er3+/Yb3+-modified PSN-PMN-PT crystals were grown by using the flux method. The effects of Er3+ and Er3+/Yb3+ modification on the crystal structure, electric, and optical properties were investigated. Phase structure of all the crystals was determined as a pure perovskite structure by the XRD. The dielectric properties of the PSN-PMN-PT crystals along [100]-orientation were enhanced significantly, and the Pr increased from 24.2 to 30.99 and 28.5 μC/cm2, respectively by the Er3+ and Er3+/Yb3+ modification. The specific absorption at the UV-VIS-NIR band and the strong green and red UC PL at 980 nm laser excitation were observed in the Er3+- and Er3+/Yb3+-modified PSN-PMN-PT crystals. The UC emission mechanisms of these modified PSN-PMN-PT crystals were also discussed.

Intense and color-tunable upconversion luminescence of Er3+ doped and Er3+/Yb3+ co-doped Ba3Lu4O9 phosphors

A series of novel Er3+ doped and Er3+/Yb3+ co-doped Ba3Lu4O9 phosphors were synthesized by a simple high-temperature solid-state reaction method. The crystal structure and morphology of the samples were identified by XRD and SEM analysis. Under 980 nm laser diode excitation, the green (at 537 nm and 560 nm) and red (at 660 nm) UC emission were observed, which could be attributed to the (2H11/2, 4S3/2)→4I15/2 and 4F9/2 → 4I15/2 transitions, respectively. The UC luminescence can be finely tuned from green to dark-yellow light to some extent by increasing Yb3+ doping concentration. The sintering temperature and doping concentration of Ba3Lu4-x-yO9: x Er3+, y Yb3+ were optimized to x = 0.1 and y = 0.6 at 1550 °C. The emission intensity ratio of Green/Red keeps declining monotonically with increasing Er3+ or Yb3+ concentration, which is due to the cross-relaxation effect and cooperative energy transfer between the two neighboring Er3+ ions-as well as back energy transfer from Er3+ to Yb3+ ions. Based on the pump-power dependence and UC luminescence decay curves, the energy level diagram and the possible energy transfer mechanism of Er3+ doped as well as Er3+/Yb3+ co-doped system were investigated in detail. In addition, according to the energy gap law, the possibilities of non-radiative transition between parts of energy levels of Er3+ ions were calculated.

Microwave hydrothermal synthesis and temperature sensing behavior of Lu2Ti2O7:Yb3+/Er3+ nanophosphors

Lu2Ti2O7:Yb3+/Er3+ (LTO:Yb3+/Er3+) nanophosphors codoped with Yb3+ (8–20 at%) and Er3+ ions (0.5–4 at%) were synthesized by a microwave hydrothermal process. Under the 980 nm excitation, the sample gives a set of upconversion light: very strong red emissions near 661 nm (4F9/2 → 4I15/2), weak green around 523 nm and 545 nm (2H11/2 → 4I15/2 and 4S3/2 → 4I15/2, respectively). The optimum doping concentrations of Er3+ and Yb3+ for the highest emission intensity were determined by photoluminescence (PL) analyses. Concentration dependent studies revealed that the optimal composition was realized for the 12 at% Yb3+ and 2.0 at% Er3+-doping concentration with a strong emission. A possible UC mechanism for LTO:Yb3+/Er3+ is discussed via the change of the pump power. The temperature dependence of the fluorescence intensity ratios (FIR) for the two green UC emission bands peaked at 523 and 545 nm was studied in the range of 298–573 K under excitation by a 980 nm diode laser and the maximum sensitivity was approximately 0.00313 K−1 at 536 K. This indicates that LTO:Yb3+/Er3+ nanophosphors are potential candidates for optical temperature sensors with high sensitivity.

Thermal and pump power effect in SrMoO4:Er3+-Yb3+ phosphor for thermometry and optical heating

The pump power and temperature dependence study in the Er3+-Yb3+ codoped SrMoO4 phosphors for the green UC emission bands has been investigated by using two NIR (980nm and 808nm) laser radiation. The thermometric behaviour of the codoped phosphor operated in the 300–543K gives maximum sensitivity ∼25.5×10−3K−1 for 980nm excitation whereas, for 808nm excitation the maximum sensitivity is ∼21.5×10−3K−1 over 300–465K. The optical heating study upon two NIR laser radiations has also been performed. The experimental observations made in this article may be of significant interest for thermometry and optical heating.

Enhanced green upconversion emission in NaYF4:Er3+/Yb3+/Li+ phosphors for optical thermometry

The NaYF4 phosphors codoped with Er3+-Yb3+ have been synthesized by hydrothermal method using oleic acid as a chelating agent. The crystal structure and surface morphology has been identified with the help of powder X-ray diffraction (PXRD) and field emission scanning microscopy (FE-SEM) technique, respectively. The presence of different functional groups in the developed phosphors have been analyzed by using the Fourier transform infrared spectroscopy (FTIR) technique. The optical non-linear behavior of the prepared phosphors has been performed by using the excitation at 980 nm from a CW diode laser. The effect of Li+ ions tri-doping on the structural and luminescence behavior of the Er3+-Yb3+ codoped NaYF4 phosphors has been discussed suitably. The effect of variation of pump power density on the UC emission intensity of different bands has been investigated. The optical temperature sensing behavior based on the green UC emissions of the Er3+-Yb3+-Li+ tri-doped NaYF4 phosphors under the excitation at very low pump power density (∼0.32 W/cm2) has been studied. The results obtained from the present study indicate that the Er3+-Yb3+-Li+ tri-doped NaYF4 phosphors may be of particular interest in developing the NIR to visible upconverters, green display devices and temperature sensors.

An effective method to detect the Curie transition of Er3+/ Yb3+ co-doped BaTiO3 ceramics by up-conversion photoluminescence intensity ratio

In this work, BaTi1−x−yO3:xEr/yYb (BTO:xEr/yYb, x = 0, y = 0; x = 0.005, y = 0.005; x = 0.01, y = 0.005; x = 0.01, y = 0.01; x = 0.015, y = 0.01) ceramics were prepared using a conventional solid-reaction method to investigate the relation between the Curie transition and up-conversion photoluminescence (UC PL) properties. We did not find that the green or red UC PL absolute intensity of Er3+ ions had any direct correlation with the Curie phase transition. However, the variation of the ratio Ig/Ir of green and red UC emission intensities with temperature has similar behavior as that of dielectric constant. An evident peak of Ig/Ir ratio was also obtained at TC in all the BTO:xEr/yYb ceramics with different Er3+/Yb3+ co-doping contents. The present study demonstrates that UC PL intensity ratio, rather than the absolute PL intensity, is an effective optical non-contact method to detect the Curie phase transition of ferroelectrics.

The ferroelectric, dielectric and up-conversion photoluminescence properties of ferroelectrics (0.99-x)PbTiO3-xPb(Yb1/2Nb1/2)O3-0.01Pb(Er1/2Nb1/2)O3

(0.99-x)PbTiO3-xPb(Yb1/2Nb1/2)O3-0.01Pb(Er1/2Nb1/2)O3 (PT-xPYN:Er, x = 0.40, 0.45, 0.50, 0.55, 0.60) ceramics were prepared by a two-step sintering technique using solid state reaction method. The phase structure, ferroelectric, dielectric and up-conversion photoluminescence (UC PL) properties of the as-prepared ceramics were investigated. The results illustrate that the phase structure, ferroelectric, dielectric and UC PL properties of the ceramics are greatly dependent on the Pb(Yb1/2Nb1/2)O3 (PYN) content x. Dispersion index γ exhibits an abnormal change at x = 0.50, 0.55, which is concerned with the phase structure of the ceramics. A strong red and a relative green UC PL were observed in the PT-xPYN:Er ceramics, in contrary with that in other hosts. Also the UC PL mechanism of Er3+ and temperature-dependent UC PL properties were discussed.

Influence of Ho3+ doping on the temperature sensing behavior of Er3+–Yb3+ doped La2CaZnO5 phosphor

Er3+/Yb3+ and Er3+/Ho3+/Yb3+ codoped La2CaZnO5 phosphors were prepared by the combustion synthesis method. The Er3+/Yb3+-codoped sample exhibited strong green and red UC emissions. The phosphors are suitable for future applications in thermometry.

NaGd(WO4)2:Yb3+/Er3+ phosphors: hydrothermal synthesis, optical spectroscopy and green upconverted temperature sensing behavior

Temperature dependence of the green UC luminescence spectra of NGW:Yb3+/Er3+ phosphor under 980 nm excitation (the spectra are normalized to the emission peak at 554 nm. The excitation power density is 3 W cm−2).

Bright dual-mode green emission and temperature sensing properties in Er3+/Yb3+ co-doped MgWO4 phosphor

The Er3+/Yb3+ co-doped MgWO4 phosphor exhibited green UC and DC emission at excited by of 980 nm (a) and 379 nm (b) light, respectively.

Investigation on the upconversion emission in 2D BiOBr:Yb3+/Ho3+ nanosheets

As lanthanide doped upconverting host, two dimensional (2D) nanostructure materials have remarkable advantages compare with the bulk materials, but excellent 2D upconversion nanohost is still few up to date. In this work, Yb3+/Ho3+ co-doped BiOBr nanosheets have been successfully prepared via a facile hydrothermal method, which were characterized by X-ray diffraction, transmission electron microscopy, Atomic Force Microscope, Raman spectra, Fourier transform infrared absorption and UC luminescence spectra. Under excitation at 980nm, bright green UC emission centered at 550nm accompanied with weak red (663nm) and near infrared (NIR) UC emissions (760nm) were observed. Power dependence studies revealed that NIR and red UC emissions were both dominated by a two and one-photon process due to saturation effects that is related to the special crystal structure of BiOBr nanosheets, and a different UC mechanism of NIR emission from Ho3+ was proposed accordingly.

Effects of aging time on phase, morphology, and luminescence by two-photon processes of BiPO4:Er3+, Yb3+ in the solvothermal synthesis

BiPO4:Er3+, Yb3+ phosphors were synthesized by the solvothermal process. The phase transformation, morphology, and UC luminescent property were characterized by different analytical techniques. The aging time has obvious influence on the phase, morphology, and luminescence of the samples. With the extension of aging time, the phase of BiPO4:Er3+, Yb3+ phosphors changes from hexagon to monocline. The morphology changes from nanorods through nanorugbies to microoctahedra. Under the excitation at 980nm, BiPO4:Er3+, Yb3+ phosphors show green and red UC emissions, which originate from the (2H11/2, 4S3/2)→4I15/2 and 4F9/2→4I15/2 transitions of Er3+ ions. The green and red UC emission intensities increase gradually with the increase of pumping power. On the basis of the luminescent properties, one can conclude that the two-photon process is involved in green and red UC emissions.

Controlled morphology and EDTA-induced pure green upconversion luminescence of Er3+/Ho3+-Yb3+ co-doped NaCe(MoO4)2 phosphor

An innovative route to increase the green UC emission and simultaneously suppress red UC emission in Er3+/Ho3+-Yb3+ co-doped NaCe(MoO4)2.