Emission Of Ho3 Research Articles

Strong green and red up-conversion emission in Ho3+, Yb3+ and Li+ co- or tri-doped SrAl2O4 ceramics

Ho3+/Yb3+ co-doped and Ho3+/Yb3+/Li+ tri-doped SrAl2O4 ceramics were prepared by the conventional solid-state reaction and their up-conversion (UC) luminescence was characterized. Strong green emission (556nm) and weak red emission (664nm) were observed under the excitation of 980nm laser diode (LD) at room temperature. The up-conversion process is based on two-photon absorption. In Ho3+/Yb3+ co-doped SrAl2O4 ceramics, the UC intensity achieved its maximum as Yb3+ concentration was 20mol% which was attributed to the energy transfer (ET) from Yb3+ to Ho3+. Furthermore, the UC green luminescence intensity was largely enhanced by about six times in Li+ doped SrAl2O4: Ho3+, Yb3+ ceramics and the related mechanisms have been discussed.

Upconversion white-light emission in Ho3+/Yb3+/Tm3+ codoped LiNbO3 polycrystals

Ho3+/Yb3+/Tm3+ codoped LiNbO3 polycrystals exhibiting upconversion white-light under 980nm excitation have been successfully fabricated by the high temperature solid-state reaction method. CIE coordinate of the Ho3+/Yb3+/Tm3+/LiNbO3 polycrystal is (0.34, 0.35), which is very close to the standard equal energy white-light illuminate (0.33, 0.33). Efficient green, red, and blue upconversion emissions have been observed. The luminescent decay dynamics are studied, and rate equations for the blue, green, and red emissions are set up to analyze the upconversion luminescence mechanism. The present results demonstrate that the competition between the linear decay and the upconversion process for the depletion of the intermediate excited states plays an important role in upconversion mechanism. The LiNbO3 with upconversion white-light will be a promising luminous material.

Optical avalanche in Ho:Yb:Gd2O3 nanocrystals

Intense green upconversion emission in Ho:Yb:Gd2O3 spherical nanoparticles is reported through hetrolooping enhanced energy transfer process. Different techniques used for structural characterization divulge the formation of spherical Ho:Yb:Gd2O3 crystals of diameter ∼100 nm. Efficient energy transfer from Yb3+ → Ho3+ ions set spherical nanocrystal to emit in the range of UV-NIR via three NIR photons absorption process. Power dependence and the temporal evolution of upconversion emission intensity suggest the occurrence of a photon avalanche process. The enhancement in emission intensity in nanophosphor sample has been explained and the photophysics involved is correlated with the unique structural properties of the crystallites formed and the time resolved spectroscopy.

Strong dependence of upconversion luminescence on doping concentration in holmium and ytterbium co-doped Y 2O 3 phosphor

Under the excitation of 980 nm diode laser, intense green emission ( 5F 4+ 5S 2- 5I 8) of Ho 3+ was observed in Ho 3+ and Yb 3+ co-doped cubic Y 2O 3. The doping concentration and laser power dependence of the upconverted emission were studied. The decay curves of 5F 4+ 5S 2 emission of Ho 3+ under the excitation of 355 nm pulse laser were measured to investigate the energy transfer process between Ho 3+ and Yb 3+. The results indicated that two-photon process was responsible for the upconversion (UC) emission. The Ho 3+ concentration of 0.04 mol.% and the Yb 3+ concentration of 5 mol.% were determined to be the best value for the strongest Ho 3+ emission under the excitation of 980 nm light. The cross-relaxation between two neighboring Ho 3+ ions and the back energy transfer from Ho 3+ to Yb 3+ were important factors for determining the optimal doping concentration. This material was a promising candidate for the application in biomedical fluorescent labels for the intense green emission upon excitation of near-infrared (NIR) light.

Single color upconversion emission in Ho 3+/Yb 3+ and Tm 3+/Yb 3+ doped P 2O 5–MgO 2–Sb 2O 3–MnO 2–AgO glasses

The Ho 3+/Yb 3+ and Tm 3+/Yb 3+ doped P 2O 5–MgO 2–Sb 2O 3–MnO 2–AgO glasses were prepared by high temperature melting method. Under a 975 nm laser diode (LD) excitation, the single red and single blue upconversion (UC) emissions were observed in Ho 3+/Yb 3+ and Tm 3+/Yb 3+ doped samples, respectively. By studying the spontaneous radiative and multiphonon relaxation probabilities, we find that the multiphonon relaxation probability of 5I 6 (Ho 3+) state is very large (1.39 × 10 6 s − 1 ), which is helpful to the population of 5I 7 state. The multiphonon relaxation probability of 3H 5 and 3F 2,3 (Tm 3+) is also very large, which results in lots of population in 3F 4 and 3H 4 states. The results are that the red UC emission of Ho 3+ and the blue UC emission of Tm 3+ are stronger.

Up-conversion emission in triply-doped Ho 3+/Yb 3+/Tm 3+ KGd(WO 4) 2 single crystals

Detailed spectroscopic studies of the triply doped KGd(WO 4) 2:Ho 3+/Yb 3+/Tm 3+ single crystals (which exhibit multicolor up-conversion fluorescence) are reported for the first time. The absorption spectra of crystals were measured at 10 and 300 K; the room temperature luminescence spectra were excited at 980 nm wavelength. The dependence of the intensity of luminescence on the excitation power for three different concentration of Ho 3+, Yb 3+ and Tm 3+ ions was investigated. Efficient green and red up-converted luminescence of Ho 3+ ions and weak blue up-conversion luminescence of Tm 3+ ions were observed in spectra. The red emission of Ho 3+ ions is more intensive than their green emission. Dependence of the up-conversion luminescence intensity on the excitation power and impurities concentration was also studied; the number of phonon needed for efficient up-conversion was determined for each case. All possible energy transfer processes between different pairs of the impurity ions' energy levels are also discussed.

Enhanced 2 μm emission of Yb–Ho doped fluorophosphates glass

In this paper, 2 μm emission spectra of Yb–Ho doped fluorophosphate glass are investigated and compared with Yb–Tm–Ho doped fluorophosphate glass. The 2 μm emission intensity of Yb–Ho doped fluorophosphate glass is much stronger than that of Yb–Tm–Ho doped fluorophosphate glass, exhibiting that Yb–Ho doping is an appropriate doping system to 2 μm application. As the doping concentration of Yb 3+ ions in Yb–Ho doped fluorophosphate glass increases, the 2 μm emission intensity increases monotonously and possesses a maximum for 10% Yb ions concentration. Therefore, 10% is the optimization of Yb ions doping concentration for 2 μm emission. Otherwise, the up-conversion emission of Ho 3+ ions is also studied. Combining with the energy transfer processes, the mechanism is discussed.

2 μm Emission of Ho 3+-doped fluorophosphate glass sensitized by Yb 3+

Two micrometer emission of Ho 3+-doped new fluorophosphate glass sensitized by Yb 3+ upon excitation of a conventional 980 nm laser diode is reported. Based on the measured absorption spectra, the Judd–Ofelt parameters and radiative properties were calculated and discussed. For Yb 3+/Ho 3+ codoped fluorophosphate glass, the predicted spontaneous transition probability and emission cross-section of Ho 3+: 5I 7→ 5I 8 reaches 73.54 s −1 and 4.66 × 10 −21 cm 2 , respectively, are much higher than other reported glasses. Larger product of emission cross-section ( σ em ) and radiative lifetime ( τ rad ) in the prepared glass shows the prepared glass is expected to be better laser material. In addition, the σ em and maximum gain coefficient of Ho 3+ in Yb 3+/Ho 3+ codoped fluorophosphate glass is 12.02% and 12.12% larger than those of Ho 3+ singly-doped sample, respectively. The results suggest Yb 3+/Ho 3+ fluorophosphate glass is a good candidate for efficient 2 μm laser.

Spectroscopic investigation of 2.02 μm emission in Ho3+/Tm3+ codoped transparent glass ceramic containing CaF2 nanocrystals

Tm 3 + and Ho3+ codoped transparent glass ceramic (GC) containing CaF2 nanocrystals were fabricated by melt-quenching and subsequent thermal treatment. X-ray diffraction and transmission electron microscopy analysis confirmed the precipitation of CaF2 nanocrystals among the glass matrix. Energy-dispersive x-ray spectroscopy results evidenced the incorporation of Tm3+ and Ho3+ into the CaF2 nanocrystals. Judd–Ofelt parameters were calculated based on the absorption spectra, the smaller Ω2 and larger Ω6 imply that Tm3+ and Ho3+ ions has entered into a symmetrical ionic crystal field. 2.02 μm emission spectral of the GC samples were recorded at room temperature with an excitation of 808 nm laser diode. The enhancement of the emission at 2.02 μm in the GC samples could be attributed to more efficient cross relaxation process of Tm3+:H34+Tm3+:H36→2Tm3+:H34, and energy transfer from Tm3+ to Ho3+ benefited from the incorporation of rare earth ions into CaF2 nanocrystals.

On competition between two types of anti-Stokes emission in Ho 3+ and Nd 3+ ions in glasses

An interesting competition between two anti-Stokes emissions has been observed and interpreted in ZBLAN and fluoroaluminate (ALF) glasses activated by Ho 3+ and Nd 3+ ions, respectively. The intensity of an emission line situated spectrally close to the excitation wavelength, was seen to increase with temperature, whereas the intensity of another, upconverted emission line, in the same conditions, was seen to decrease. Both effects are believed to be caused by the same mechanism, which we have identified as the anti-Stokes multiphonon excitation of the state responsible for the first emission, followed by upconversion of the ESA (excited state absorption) or an energy transfer type process. Analysis of the kinetics of the observed effects enabled us to fit a theoretical model to the experimental data. It appears likely that the described competition may be a universal feature not restricted to the materials described in this work.

Upconversion color tunability and white light generation in Tm 3+/Ho 3+/Yb 3+ doped aluminum germanate glasses

Tm 3+/Ho 3+/Yb 3+ triply doped aluminum germanate glasses exhibiting multicolor upconversion fluorescences have been fabricated and characterized. Efficient three-photon blue upconversion emission of Tm 3+ and two-photon green and red upconversion fluorescences of Ho 3+ have been observed. The strong red emission of Ho 3+, which is more than eight times higher than that of the green emission, is desirable in achieving high color rendering index. By varying the excitation power of the 974 nm wavelength laser diode, a series of white fluorescences with a large range of correlated color temperature ( CCT) was obtained, and the fluorescence colors can be tuned from yellowish white to warm white, pure white, cool white, and bluish white with different CCT. The upconversion color tunability via pump power adjustment will promote the development of three-dimensional solid-state displays and upconversion illumination devices.

Competition between two types of anti-Stokes emission inHo3+-activated ZBLAN glass

A competition between two anti-Stokes emissions has been observed and interpreted in ZBLAN glassactivated by Ho3+ ions. The first anti-Stokes emission intensity was seen to increase with temperature,whereas another, upconverted emission, was seen to decrease under the same conditions.Both observed tendencies are believed to be caused by the same effect: the multiphononanti-Stokes excitation of the state responsible for the first emission. Analysis of thekinetics and fits of the theoretical model to experimental data are presented.

Spectral properties and energy transfer of Tm 3+/Ho 3+-codoped Ga 2O 3-Bi 2O 3-GeO 2-PbO glasses

The 2.0 μm emission originating from Ho 3+: 5I 7 → 5I 8 transition in Ho 3+/Tm 3+-codoped gallate-bismuth-germanium-lead glasses were investigated upon excitation with 808 nm laser diode (LD). Energy transfer (ET) process between Tm 3+: 3F 4 level and Ho 3+: 5I 7 level was also discussed. It was noted that the measured peak wavelength and stimulated emission cross-section of Ho 3+-doped bismuth-germanium-lead glasses were ∼2.02 μm and 5.1×10 −21 cm 2, respectively. Intense emission of Ho 3+ in Tm 3+/Ho 3+-codoped GBPG glass were observed, which resulted from the ET between Tm 3+: 3F 4 and Ho 3+: 5I 7 level upon excitation with 808 nm LD.

Sensitized holmium upconversion emission in LiNbO3 triply doped with Ho3+, Yb3+, and Nd3+

Observed is 15 times enhancement of Ho3+ green upconversion (UC) emission in Ho3+(0.75 mol %)/Nd3+(0.75 mol %) doped lithium niobate crystal after incorporating with 4 mol % of Yb3+ under 800 nm femtosecond laser excitation. Yb3+ acting as bridging ion increases the energy transfer efficiency from Nd3+ F43/2 level to Ho3+ in these triply doped systems. The nonradiative energy transfer efficiency from Nd3+ F43/2 to Yd3+ F25/2 level can reach to 56%. The UC emission mechanisms are proposed based on spectral, kinetic, and pump power dependence analyses. The green UC emission is accomplished through a multi-ion interaction involving ground state absorption by the Nd3+ (I49/2→H29/2,F45/2) followed by three successive energy transfer processes involving one Nd3+-Yb3+ (F43/2+F27/2→I49/2+F25/2) and two Yb3+-Ho3+ pairs (F25/2+I58→F27/2+I56 and F25/2+I56→F27/2+S52,F54); whereas the red is dominated by excited state absorption of the Ho3+ (I57→F55) following two successive energy transfer processes involving the Nd3+-Yb3+ (F43/2+F27/2→I49/2+F25/2) and Yb3+-Ho3+ pairs (F25/2+I58→F27/2+I56) followed by the Ho3+ nonradiative relaxation to I57.

Fluorescence investigation of Ho 3+ in Yb 3+ sensitized mixed-alkali bismuth gallate glasses

Efficient 2.0 μm infrared and visible upconversion emissions have been observed in Ho 3+/Yb 3+ co-doped mixed-alkali bismuth gallate (LKBBG) glasses having a maximum-phonon energy of 673 cm −1. The Judd–Ofelt parameters Ω 2, Ω 4 and Ω 6 of Ho 3+ indicate that there is a high asymmetry and strong covalent environment in LKBBG glasses. The large absorption and emission cross-sections of Yb 3+ confirm that it is a suitable sensitizer for capturing and transferring pump energy to Ho 3+. The emission cross-section profile for the 5I 7 → 5I 8 transition is derived using the reciprocity method and the peak value is 5.54 × 10 −21 cm 2, which is much larger than the value in fluorozircoaluminate glasses. LKBBG glasses exhibit low maximum-phonon energy and large refractive index, and it is possible to achieve an effective 1.66 μm U-band emission of Ho 3+ under 900nm laser radiation.

Mid-Infrared Emission Characteristic and Energy Transfer of Ho3+-Doped Tellurite Glass Sensitized by Tm3+

We report on 2.0-microm emission characteristic and energy transfer of Ho3+-doped tellurite glass sensitized by Tm3+ upon excitation of a conventional 808 nm laser diode. The Judd-Ofelt strength parameters, spontaneous radiative transition probabilities and radiative lifetime of Ho3+ have been calculated from the absorption spectra by using the Judd-Ofelt theory. Significant enhancement of 2.0-microm emission of Ho3+ has been observed with increasing Tm3+ doping up to 0.7 mol%. The energy transfer coefficient of the forward Tm3+-->Ho3+ is approximately 17 times larger than that of the backward Tm3+<--Ho3+ energy transfer. Our result indicates that the maximum gain of 2.0-microm emission, assigned to the transition of (5)I7-->(5)I8 of Ho3+, might be achieved from the tellurite glass at the concentration of 0.5 mol% of Tm2O3 and 0.15 mol% of Ho2O3. The high gain coefficient and quantum efficiency (1.16) along with the large value of the product of the stimulated emission cross-section and the measured radiative lifetime (4.12 x 10(-27) m(2)s) of the Ho3+/Tm3+-codoped tellurite glasses might find potential applications in efficient 2.0-microm laser.

Ho 3+:TeO 2 glass, a probe for temperature measurements

Considerable effort has recently been devoted to the development of optical fiber based temperature monitoring device owing to their advantage over conventional thermometric techniques. Optical thermometry based upon near infrared excited upconversion fluorescence emission in Ho 3+ activited tellurite glasses excited at 890 nm is presented. Temperature sensing in the range 265–440 K within 2 K accuracy using excitation powers readily obtainable from commercially available Ti–sapphire laser have been achieved. This temperature sensing approach is independent of fluctuations in excitation intensity, environment, transmission and requires a simple and low cost signal detection and processing system. Our results also indicate that the glassy host material also plays a major role in the process of the temperature sensing capacity.

Spectroscopic investigation of 2.0 µm emission in Ho3+-doped fluoroindate glasses

In this paper we report the optical characterization of Ho3+-doped fluoroindate glasses with the following composition (40 − x)InF3–20SrF2–16BaF2–20ZnF2–2GdF3–2NaF–xHoF3 with x = 1.0, 2.0, 2.5, 3.0, 4.0, 5.0, 6.0, 8.0 and 9.0 mol%. This investigation was done by means of absorption, fluorescence and lifetime measurements. The phenomenological intensity parameters Ωλ (λ = 2, 4, 6) were calculated using the standard Judd–Ofelt theory. In order to evaluate potential applications of the 5I7 → 5I8 Ho3+ emission at 2.0 µm, the radiative lifetime, total transition rate and emission cross section were determined. The effect of Ho3+ concentration on the fluorescence intensity and lifetimes was analysed. It was concluded that the non-radiative losses of the 5I7 level are mainly due to energy migration among Ho3+ ions followed by energy transfer to quenching impurities.

Upconversion-induced ultraviolet emission in Ho3+ doped SrLaGa3O7 and SrLaGaO4 crystals

An analysis of the red to ultraviolet wavelength upconversion in Ho3+ in SrLaGa3O7 and SrLaGaO4 crystals is given. Upconverted, ultraviolet emission from the 3D3 level under cw 647nm excitation at room temperature was observed. Excitation of the 5F5 level, corresponding to the 5I8→5F5 transition, leads to intense emission from the 5I7, 5I6, 5F5, 5S2, 5F3, 3G5 and 3D3 levels. Based on the energy level diagram of Ho3+, the pump intensity dependencies and experimental time dependencies of the observed emissions, an excitation scheme is proposed.

An experimental study on engine performance with high ignition energy

The objective of this research is to investigate the improvement of engine performance with high ignition energy. In order to study this objective, two different spark ignition engines are employed and four different ignition systems are adopted. The ignition energy, combustion pressure, exhaust gases and fuel consumption are measured to evaluate engine performances. In addition, the heat release rate, mass fraction burned and coefficient of variation (COV) of indicated mean effective pressure (IMEP) are calculated with the measured pressures. The results reveal that high ignition energy shortens the combustion duration, improves the engine stability and reduces fuel consumption. When a higher ignition energy is applied to a lean mixture, the emission of hydrocarbons (HC) is reduced while an engine with the conventional ignition energy produces higher HO emission. A faster heat release rate and a higher mass fraction burned also result. When the same amount of ignition energy is applied to a lean mixture, the burning velocity is slow as the discharge duration becomes longer, but the COV of IMEP is improved.