Upconversion Luminescence Of Ho3 Research Articles

Extremely intense pure green upconversion luminescence in Ho3+/Yb3+ co-doped BiTa7O19 phosphors under 980 nm laser excitation

Extremely intense pure green upconversion luminescence in Ho3+/Yb3+ co-doped BiTa7O19 phosphors under 980 nm laser excitation

Infrared to visible upconversion luminescence in Ho3+ doped oxyfluoride glass ceramics

Infrared to visible upconversion luminescence in Ho3+ doped oxyfluoride glass ceramics

Synthesis and up-conversion luminescence of Ho3+ and Yb3+ co-doped La7P3O18 phosphors

Ho3+ and Yb3+ co-doped La7P3O18 up-conversion phosphors were prepared by a high-temperature solid-state process. XRD results reveal that the samples are mixtures of monoclinic structure La7P3O18 crystals with P21/n space group and minor LaPO4 crystals. UV—Vis DRS results indicate that La7P3O18 crystal is an indirect semiconductor with an optical band gap of 4.10 eV. After 980 nm laser excitation, the Ho3+ and Yb3+ co-doped La7P3O18 phosphors show the characteristic blue (486 nm), green (550 nm), and red (661 nm) luminescence peaks of Ho3+ ions. The peak at 661 nm dominates in the up-conversion luminescence spectra of samples. Meanwhile, with the increase of Ho3+ and Yb3+ doping content, the up-conversion luminescence intensity increases first and then decreases. By increasing the doping contents of Ho3+ and Yb3+ up to 1 at.% and 10 at.%, respectively, concentration quenching may appear by an electric quadrupole– electric quadrupole interaction process. The pumping power dependence of luminescence indicates that the green and red emissions of samples are excited by a two-photon absorption process. The color coordinates of Ho3+ and Yb3+ co-doped La7P3O18 crystals locate in the orange—red region.

Photon upconversion luminescence in Ho3+/Yb3+ doped Sr2YF7 nanophosphors synthesized by wet chemical method

Ho3+ (0.5, 1.0 mol%) / Yb3+ (5.0 mol%) co-doped Strontium Yttrium Fluoride upconversion nanophosphors are prepared by wet chemical method. Structural and morphological studies are carried out by X-ray diffraction (XRD), Field-emission scanning electron microscopy (FE-SEM) and energy dispersive X-ray spectroscopy (EDXS). The XRD and FE-SEM results show single-phase Sr2YF7 nanocrystals formation. The Upconversion Photoluminescence study is carried out using 980 nm laser excitation. The Yb3+ acts as an efficient energy transfer medium due to absorption around 980 nm. The upconversion study shows that the energy-transfer from Yb3+ to Ho3+ is successful in Sr2YF7 host matrix.

Up-conversion luminescence tuning induced by cross-relaxation processes in Gd2O3: Yb3+/Ho3+/Ce3+ nanoparticles

In this work, we reported the influences of Ce3+ doping on continuous and pulse 980 nm laser excited up-conversion luminescence of Gd2O3: Yb3+/Ho3+. Under continuous excitation at 980 nm, a 7.6-fold up-conversion red-to-green ratio enhancement was achieved by co-doping Ce3+ into Gd2O3: Yb3+/Ho3+, which could be attributed to two effective Ho3+-Ce3+ cross-relaxation processes. Besides, introducing Ce3+ also induced the more significant enhancement in the red to green intensity ratio with increasing the excitation pulse-widths of 980 nm laser in comparison to the sample without Ce3+. The results were contributed to better understand the influence of Ce3+ doping on the up-conversion luminescence of Ho3+, especially under the non-continuous excitation, endowing us with the more opportunities to control the up-conversion color output for satisfying diverse applications in a multitude of fields.

Infrared-laser and upconversion luminescence in Ho3+-Yb3+ codoped tellurite glass microsphere

In this letter, Ho3+-Yb3+ codoped tellurite glasses were fabricated using the melting-quenching method to produce optical microsphere cavities. A 980 nm excitation laser was coupled into the microsphere through a fiber taper, providing lasing at around 2.0 μm and upconversion luminescence in the visible (380–780 nm).

Hydrothermal Synthesis and Up‐conversion Luminescence of Ho3+/Yb3+ Co‐doped PbTiO3

Ho3+/Yb3+ co‐doped PbTiO3 nanocrystals with different content of dopant were successfully prepared via a facile hydrothermal method. The purity, morphology, element distribution, chemical state and up‐conversion (UC) photoluminescence (PL) of PbTiO3 nanocrystals affected by Ho3+ dopant are investigated systematically. X‐ray diffraction (XRD) results illustrate that PbTiO3 samples with the doping Ho3+ concentration ranging from 0 to 5 mol‐% are perovskite structure. The doping Ho3+ ions have no change on the crystal structure of perovskite PbTiO3. Owing to the non‐equivalent substitution of Ho3+ to Ti4+ in PbTiO3, the particle size of Ho3+/Yb3+ co‐doped PbTiO3 samples is decreased as well as the particle agglomeration is detected. Moreover, Ho and Yb ions have uniform distributions in the PbTiO3 nanoparticles as the presence of Ho3+ and Yb3+ cations. The up‐conversion spectra demonstrate that Ho/Yb co‐doped PbTiO3 samples have up‐conversion emissions centered at 550 nm, 660 nm and 755 nm, corresponding to the transitions of 5F4(5S2)→5I8, 5F5→5I8 and 5S2(5F4)→5I7 of Ho3+ ions. Additionally, the effect of temperature on the UC PL property of Ho3+/Yb3+ co‐doped PbTiO3 system is further investigated. The sensitivity and the trend of Ho3+/Yb3+ co‐doped PbTiO3 samples in temperature from 298 k to 493K are calculated on the basis of fluorescence intensity ratio (FIR) method. Ho3+/Yb3+ co‐doped PbTiO3 nanocrystals are verified the high potential in the optical temperature sensing.

Effect of Ho3+ and Tm3+ concentration on UV-VIS-NIR and upconversion luminescence in Ho:Tm:LiNbO3 crystals

Abstract Ho:Tm:LiNbO3 crystals with x mol% Ho3+ ions and y mol% Tm3+ ions (x = 0.1, 0.2, 0.25 and 0.3, y = 1, 2, 2.5 and 3) were grown by the Czochralski method. The influence of Ho3+ ions and Tm3+ ions concentration on the UV-VIS-NIR absorption spectra was discussed. The upconversion luminescence of Ho3+ and Tm3+ ions was observed under 800 nm excitation, and the energy transfer mechanisms of upconversion process were analyzed in details. The energy transfer mechanisms reflect that cross relaxation (CR), excited state absorption (ESA) and energy transfer (ET) from 3F4 (Tm3+) to 5I7 (Ho3+) are responsible for the upconversion emissions. The blue emission at around 473 nm, green emission at around 544 nm and red emission at around 648 nm were both enhanced obviously by doping 0.3mol% Ho3+ ions and 3mol% Tm3+ ions. The results show that Ho:Tm:LiNbO3 crystal is an excellent potential laser medium.

Investigation on the upconversion luminescence in Ho3+/Yb3+ co-doped Ba3Sc4O9 phosphor

A series of Ba3Sc4O9:Ho3+/Yb3+ phosphors were synthesized by a high-temperature solid-state reaction method. The phase purity and upconversion luminescence were characterized by X-ray diffraction and photoluminescence spectroscopy. The sintering temperature and doping concentrations were optimized to obtain the strongest emission intensity. Under 980nm laser diode excitation, the green (545nm, 5F4/5S2→5I8) and red (665nm, 5F5→5I8) emissions were observed. The cross-relaxation and back-energy-transfer processes play an important role to adjust the emission intensity ratio of Green/Red at different dopant concentrations. Based on the energy level diagrams, the energy transfer mechanisms are investigated in detail according to the analysis of pump power dependence and luminescence decay curves. The upconversion luminescence properties of the phosphor were evaluated and the results show good color monochromaticity and relatively high upconversion luminescence intensity. The Ba3Sc4O9:Ho3+/Yb3+ can be a good candidate for green upconversion material in display fields and fluorescent labeling.

Influence of pump power and doping concentration for optical temperature sensing based on BaZrO3:Yb3+/Ho3+ ceramics

The knowledge of the impact of the pump power and the doping concentration is valuable importance for optical temperature sensors. Ho3+/Yb3+ co-doped BaZrO3 ceramics were prepared successfully, and its structure is studied by XRD and SEM. The upconversion luminescence of Ho3+/Yb3+ co-doped BaZrO3 ceramics were studied at different doping concentration and pump power. By using fluorescence intensity ratio method, the temperature sensing behaviors were observed in temperature range of 300–580K based on non-thermal coupled levels 5S2, 5F5 → 5I8, and 5S2 → 5I7, 5I8. The maximum relative sensitivity is 36.35%K−1 at 525K, which is based on non-thermal coupled levels 5S2 → 5I7, 5I8 under pump power of 90mW with doping concentration 0.5mol%.

Analysis of excitation mechanisms of Ho3+ upconversion luminescence in Ho3+:LiYbF4 (0.2 at %) crystal via photographs of its longitudinal cross sections and via spectral and kinetic characteristics

The results of a complex analysis of the excitation mechanisms of the up conversion luminescence of Ho3+:LiYbF4 (0.2 at %) crystal are presented. The spatial distribution of the upconversion luminescence intensity is studied by the photographs of longitudinal cross sections at different positions of the laser beam waist with respect to the sample. The surface power density of the pump laser diode radiation (0.755 W, λ = 933 nm) was changed by focusing the beam (similar to Z-scanning). The dependences of the longitudinal luminescence cross sections, as well as of the spectral and kinetic characteristics of Ho3+ and Yb3+ luminescence, on the position of the laser beam waist are determined. It is found that there exist two different mechanisms of the population of the energy levels of Ho3+ ions from which green and red luminescence occur, namely, cooperative sensitization of luminescence and absorption of induced photon groups (JETP Letters, 102 (5), 279 (2015)). It is shown that the contributions of these mechanisms vary both in time and over the crystal volume. All the observed spatial, spectral, and temporal specific features of the upconversion luminescence of Ho3+:LiYbF4 (0.2 at %) crystal are qualitatively explained.

Up-conversion luminescence of Ho3+/Yb3+/Er3+ co-doped oxy-fluoride glass

ABSTRACTHo3+/Yb3+/Er3+ co-doped fluoride silicate glass is prepared, and the excitation spectra of the glass is tested. Under excitation of 980 nmLD, the energy transfer between Ho3+ and Er3+ and Ho3+ up-conversion fluorescence are studied with analysis of Ho3+ ions up-conversion mechanism, it can be found that the green light appeared in 549 nm mainly results from: Er3+: 4S3/2→4I15/2, Ho3+: 5S2→5I8 transition interaction and in the same way red light in 658 nm is mainly due to Er3+: 4F9/2→4I15/2, Ho3+: 5F5→5I8 transition interaction. The fluorescence intensity of the samples with different doping concentration found that best doping concentration on Ho3+ is 0.2 mol %.

Upconversion luminescence of Ho3+/Yb3+ co-doped CaNb2O6 thin films

Ho3+/Yb3+ co-doped CaNb2O6 thin films were deposited on Si(100) substrates by pulsed laser deposition and annealed at different temperature in air atmosphere. The structure and properties of the film samples were characterized by using X-ray diffraction, atomic force microscope, Raman spectroscopy, X-ray photoelectron spectroscopy and photoluminescence spectra. It is found that the annealing temperature has a strong effect on the film's structure, morphology, grain size and the up-conversion luminescence properties. Upconversion luminescence intensity of Ho3+/Yb3+ co-doped CaNb2O6 films is enhanced by increasing the annealing temperature.

Investigation of the mechanisms of upconversion luminescence in Ho3+ doped CaF2 crystals and ceramics upon excitation of 5I7 level

The mechanisms of upconversion luminescence of CaF2:Ho crystals and ceramics from 5F3, 5S2(5F4), 5F5 and 5I6 levels upon excitation of 5I7 level of Ho3+ ions were investigated. Different mechanisms are responsible for the populating and depletion of the energy levels of Ho3+ ion in CaF2:Ho crystals and ceramics upon excitation of 5I7 level. The upconversion luminescence from 5F3, 5F5, and 5I6 levels in CaF2:Ho crystals and ceramics is explained by energy transfer upconversion processes. Our results also confirmed that both excited-state absorption and energy transfer upconversion are responsible for the populating of 5S2(5F4) level.

Optical transitions of Ho3+ in oxyfluoride glasses and upconversion luminescence of Ho3+/Yb3+-codoped oxyfluoride glasses

Optical properties of Ho3+-doped SiO2–BaF2–ZnF2 glasses have been investigated on the basis of the Judd–Ofelt theory. Judd–Ofelt intensity parameters, radiative transition probabilities, fluorescence branching ratios and radiative lifetimes have been calculated for different glass compositions. Upconversion emissions were observed in Ho3+/Yb3+-codoped SiO2–BaF2–ZnF2 glasses under 980nm excitation. The effects of composition, concentration of the doping ions, and excitation pump power on the upconversion emissions were also systematically studied.

Upconversion luminescence and mechanisms of Nd3+/Ho3+/Yb3+ triply doped TeO2–K2O–Nb2O5 glasses

Nd3+/Ho3+/Yb3+ triply doped TeO2–K2O–Nb2O5 glasses were synthesized by the conventional melting-quenching technique. Single green upconversion (UC) luminescence centered at 532nm, corresponding to the (5F4, 5S2)→5I8 transitions of Ho3+, was observed under 800nm excitation. However, green and red emission bands centered at 547, 662 and 758nm, corresponding to the (5F4, 5S2)→5I8, 5F5→5I8 and (5F4, 5S2)→5I7 transitions of Ho3+, respectively, were simultaneously observed under 980nm excitation. The dependence of UC luminescence intensity of Ho3+ under 800 and 980nm excitations on Yb3+ concentration was studied. It was found, under 800nm excitation, the 532nm emission intensity of Ho3+ begin to reduce when the Yb3+ concentration is higher than 0.8mol%. However, at the same concentration of Yb3+, the emission quenching was not observed under 980nm excitation. The UC mechanisms under two pumping sources were discussed in terms of the experiment results. It was found that the UC luminescence of Ho3+ mainly depends on ET under 800nm excitation; however under 980nm excitation, it mainly depends on ESA.

Hydrothermal synthesis and up-conversion luminescence of Ho3+/Yb3+ co-doped CaF2

CaF2:Ho3+/Yb3+ nano-particles with intense green up-conversion (UC) luminescence are successfully synthesized via a facile hydrothermal approach by using NH4F as the fluoride source and Na2EDTA as a chelating reagent. Powder X-ray diffraction (XRD), transmission electron microscopy (TEM), field emission scanning electron microscopy (FE-SEM), and UC emission spectra are used to characterize the structures, shapes, and luminescent properties of the samples. The effects from fluoride sources and chelating reagents on the formations of CaF2 nano-particles are investigated, and the formation process is also deduced. Under the excitation of a 980-nm laser diode, the samples each show a green up-conversion emission centered at 540 nm corresponding to the 5S2/5F4→5I8 transitions of Ho3+. Moreover, the UC mechanisms of Ho3+/Yb3+ co-doped CaF2 nano-particles are also discussed.

Microstructure and upconversion luminescence in Ho3+ and Yb3+ co-doped ZnO naocrystalline powders

The Ho3+/Yb3+ co-doped ZnO nanocrytalline powders were fabricated by a facile hydrothermal route. The structure and morphology of the samples were studied by XRD and SEM, respectively. The upconversion luminescence properties of the Ho3+/Yb3+ co-doped ZnO samples were investigated under 980nm excitation. The upconversion emission bands centered at 545 and 660nm corresponding to 5F4+5S2→5I8 and 5F5→5I8 transitions of Ho3+ ion, respectively, were observed. The dependence of the upconversion emission intensity upon the Yb3+ ions concentration was also examined. Power studies revealed that a two-photon process was involved in the upconversion emissions and the possible upconversion mechanisms were discussed.

Yellow upconversion luminescence in Ho3+/Yb3+ co-doped Gd2Mo3O9 phosphor

The strong yellow upconversion (UC) light emission was observed in Ho3+/Yb3+ co-doped Gd2Mo3O9 phosphor under the excitation of 980 nm diode laser. The phosphors were synthesized by the traditional solid-state reaction method. The structures of the samples were characterized by X-ray diffraction (XRD). Under 980 nm excitation, Ho3+/Yb3+ co-doped Gd2Mo3O9 exhibited strong yellow UC emission based on the green emission near 541 nm generated by 5F4,5S2 → 5I8 transition and the strong red emission around 660 nm generated by 5F5 → 5I8 transition, which assigned to the intra-4f transitions of Ho3+ ions. The doping concentrations of Ho3+ and Yb3+ were determined to be 0.01 mol Ho3+ and 0.2 mol Yb3+ for the strongest yellow emission. Then the dependence of UC emission intensity on excitation power density showed that the green and red UC emissions were involved in two-photon process. The possible UC mechanisms for the strong yellow emission were also investigated. The result indicated that this material was a promising candidate for the application in the yellow display field.

Influence of temperature on upconversion multicolor luminescence in Ho^3+/Yb^3+/Tm^3+-doped LiNbO_3 single crystal

The temperature dependence of upconversion luminescence in Ho3+/Yb3+/Tm3+ tri-doped LiNbO3 single crystal was studied at different temperatures from 289 to 773 K under 980 nm excitation. The tri-doped LiNbO3 single crystal offers temperature-dependent color tuning properties, and the white-light emission can be obtained by simply tuning the temperature. In addition, the competition between nonradiative transition and thermal population plays an important role in the upconversion process with temperature increase. This research has implications in the extension of research for optical temperature sensors and multicolor variable temperature display materials.