Strong Upconversion Emission Research Articles

A New Blue, Green and Red Upconversion Emission Nanophosphor: BaZrO3:Er,Yb

Strong Blue, green, and red upconversion emission of Er3+ in nanocrystalline BaZrO3:(Yb3+Er3+) is observed. Powder samples were obtained by a facile hydrothermal process at 100 degrees C. The as synthesized nanocrystallites preserve a stable cubic perovskite phase under subsequent annealing treatment up to 1000 degrees C. No other phase or segregation of other compounds was detected. Crystallites sizes were around 115 nm and well faceted. Under IR excitation in the range between 900 and 1050 nm the Er3+ blue emission was almost not present in single Er3+ doped BaZrO3, whereas it became easily observable when Yb3+ was added as codopant. Besides, both green and red upconversion emission or upconverted signal of Er3+ are enhanced by around three orders of magnitude in comparison with the single Er3+ doped BaZrO3. The strong blue emission presents dependence on both excitation power and excitation wavelength. This is the first time that upconversion emission is observed in BaZrO3. A possible mechanism for the upconversion process that leads to the observed blue, green and red emissions under NIR excitation is suggested based on the experimental results.

Blue-green upconversion emission in ZrO2:Yb3+ nanocrystals

Strong blue-green cooperative upconversion emission was observed under infrared excitation in 70 nm average crystallite size ZrO2:Yb3+ nanocrystals prepared by sol-gel process. The structural characterization was performed by x-ray diffraction and high resolution transmission electron microscopy suggesting that crystalline phase of nanoparticles is controlled by active ion concentration. The cooperative absorption coefficient η∼2.5×10−22 is four orders of magnitude larger than the ones reported from bulk crystals. The highest emission intensity was obtained from the doped sample at 4 mol % and was the result of the simultaneous relaxation of two excited Yb ions. Decay time of the upconverted signal τCUC≈0.310 ms is half from the near infrared effective decay time confirming the cooperative process among Yb ions. Such strong cooperative effect is explained in terms of interaction enhancement due to the diminishing of Yb–Yb separation promoted partly by the surface recombination of nanocrystals.

Red up-conversion emission from nanocrystalline GaN powders co-doped with Er 3+ and Yb 3+

The synthesis, structure, and spectroscopy of frequency upconverting lanthanide doped GaN nanocrystals (NCs) are presented. The crystalline wurtzite GaN NCs were synthesized via a nitridation reaction of β-Ga 2O 3 in a flow of anhydrous ammonia. The average sizes of GaN nanocrystallites as determined from XRD and TEM measurements was 30 nm. The photoluminescence (PL) spectra under 980 nm laser diode excitation was measured and analyzed. It was found that GaN Er 3+ and Yb 3+ doped nanocrystalline powders exhibit strong red up-conversion (UC) emission. The mechanisms and pathways of UC are also briefly discussed.

Strong visible up-conversion emissions and thermometric applications of Er3+–Yb3+ codoped Al2O3 prepared by the sol–gel method

The Er3+–Yb3+ codoped Al2O3 has been prepared by the sol–gel method using the aluminium isopropoxide [Al(OC3H7)3]-derived Al2O3 sols with addition of the erbium nitrate [Er(NO3)3 · 5H2O] and ytterbium nitrate [Yb(NO3)3 · 5H2O]. The phase structure, including only two crystalline types of doped Al2O3 phases, θ and γ, was obtained for the 1 mol% Er3+ and 5 mol% Yb3+ codoped Al2O3 at the sintering temperature of 1,273 K. By a 978 nm semiconductor laser diodes excitation, the visible up-conversion emissions centered at about 523, 545, and 660 nm were obtained. The temperature dependence of the green up-conversion emissions was studied over a wide temperature range of 300–825 K, and the reasonable agreement between the calculated temperature by the fluorescence intensity ratio (FIR) theory and the measured temperature proved that Er3+–Yb3+ codoped Al2O3 plays an important role in the application of high temperature sensor.

Er3+ and Yb3+ concentration effect in the spectroscopic properties and energy transfer in Yb3+/Er3+ codoped tellurite glasses

Spectroscopic properties of Yb3+/Er3+ codoped tellurite glasses as a function of Er3+ and Yb3+ concentration have been investigated. Under 970 nm excitation three strong up-conversion emission bands centred at 525, 546 and 656 nm were observed, and the characteristic near infrared emission band was centred at 1.53 µm. With fluorescence and radiative lifetime the quantum efficiency (QE) of infrared (1.53 µm) and visible upconversion (546 and 660 nm) emissions was calculated. The maximum stimulated emission cross section for 4I13/2 → 4I15/2 transition of Er3+ is 9.7 × 10−21 cm2 for 3/0.5 mol%. The energy transfer (ET) efficiency from Yb3+ to Er3+ (4F5/2) + (4I15/2) → (4 F7/2) + (4I13/2) was calculated, being the maximum ET of 69% for 0.5 mol% of Er3+ with 4.5 mol% of Yb3+. The results indicate that both ET and QE depend mostly on Er3+ rather than on Yb3+ concentration.

Arc discharge synthesis and up-conversion emissions of Er 3+ doped Al 2O 3 nanoparticles

The Er 3+ doped Al 2O 3 nanoparticles with an average particle size of about 50 nm have been synthesized by an arc discharge synthesis method. The strong up-conversion emissions centered at about 526, 547, and 668 nm were detected by a 978 nm laser diode (LD) excitation. The evident effect of annealing on the up-conversion emissions of the samples was studied. Before annealing, the red up-conversion emission was noticeable because of a high transition probability of the 4I 13/2 + a photon → 4F 9/2. However, the green up-conversion emission became predominant due to an enhancement of the 4I 11/2 + a photon → 4F 7/2 and 4I 11/2 + 4I 11/2 → 4F 7/2 processes after annealing. The results proved that arc discharge synthesis is a new promising preparation technology for optical materials.

Analysis of the dynamics of upconversion in erbium-doped transparent lead lanthanum zirconate titanate ceramic

The absorption and upconversion fluorescence spectra of Er3+ ions in Er3+ doped transparent lead lanthanum zirconate titanate(PLZT)ceramic were measured at room temperature. The radiative transition probabilities of the Er3+ ions were calculated using the absorption spectrum of Er3+ doped PLZT. Strong upconversion emission was observed in the upconversion luminescence of Er3+ doped PLZT. The green emission intensities at 540nm and 564nm were stronger than the red emission intensity at 678nm. The upconversion rate equations describing the dynamic process of the system have been deduced. The upconversion coefficients were estimated by numerically solving the rate equations and fitting the simulated curves to the measured data. The coefficients C22and C33 obtained are 091×10-18cm3/s and 1823×10-18cm3/s, respectively. The results show that evident upconvesion phenomenon can be observed in Er3+: PLZT transparent ceramics, which is consistent with our observation.

Highly efficient cooperative up-conversion of Yb3+ in NaYF4

Strong blue cooperative up-conversion emission around 475 nm has been observed in Yb3+-doped hexagonal NaYF4. The influence of concentration of the Yb3+ ion on the luminescence intensity is investigated. It is found that the sample shows the strongest cooperative luminescence when the Yb3+ ion concentration is 75%. The investigation shows that hexagonal NaYbF4 is an efficient blue up-converted phosphor, which might be potentially applicable in three-dimensional solid-state fluorescence display.

Spectroscopic properties of Er 3+-doped and Er 3+/Yb 3+-codoped PbF 2–MOx (M = Te, Ge, B) oxyfluoride glasses

A series of Er 3+-doped and Er 3+/Yb 3+-codoped lead germanate (GP), lead tellurite (TP) and lead borate (BP) transparent oxyfluoride glasses were synthesized. Spectroscopic characteristics of these materials were systemically measured. The Judd–Ofelt parameters were calculated according to absorption spectra. F − ions have a strong effect on refractive index ( n) and phonon energy of the host. Intense red and green upconversion is closely related to phonon energy, J–O parameters and sensitizer. The GPEY-2 glass (53GeO 2–43PbF 2–0.5Er 2O 3–2Yb 2O 3) shows good transparency and fairly strong upconversion emissions.

Controlled Hydrothermal Growth and Up-Conversion Emission of NaLnF4 (Ln = Y, Dy−Yb)

The controlled hydrothermal preparation of NaYF(4) as both cubic and hexagonal phase types with specific associated morphologies, nanospheres and microtubes, respectively, has been achieved in the absence of organic solvents. The hexagonal NaYF(4) compound can be prepared in novel microtubular form and directly co-doped with Yb(3+)/Er(3+) ions. When excited by infrared light of 980 nm, these hexagonal NaYF(4) microtubes display strong green up-conversion emission, which was much more intense than that of cubic NaYF(4) or hexagonal NaYF(4) nanoparticles. Other related hexagonal-prismatic microtubes of NaLnF(4) (Ln = Dy-Yb) were also synthesized. A growth mechanism for the microtubes is proposed. In general, the diameter of the hexagonal NaLnF(4) microtubes is strongly dependent on the Ln(3+) size and increases as the rare-earth ionic radius decreases.

Red and green upconversion luminescence of Gd 2O 3:Er 3+, Yb 3+ nanoparticles

Gd 2O 3:Er 3+, Yb 3+ nanoparticles have been synthesized by a homogeneous precipitation method with EDTA 2Na of two different concentrations. Upconversion luminescence spectra of the samples have been studied under 980 nm laser excitation. The results of XRD show that obtained Gd 2O 3:Er 3+, Yb 3+ nanoparticles are of a cubic structure. The average crystallite sizes could be calculated as 22 and 29 nm, respectively. The strong green and red upconversion emission were observed, and attributed to the 2H 11/2, 4S 3/2 → 4I 15/2 and 4F 9/2 → 4I 15/2 transitions of Er 3+ ion, respectively. The ratio of the intensity of green emission to that of red emission has drastic changed with an EDTA 2Na concentration changed. The intention of green and red emission controlled in Gd 2O 3:Er 3+, Yb 3+ nanocrystals is achieved by a varying concentration of EDTA 2Na, and the possible mechanisms are discussed.

Strong visible up-conversion emission in Tb 3+, Tm 3+ and Tb 3+–Tm 3+ co-doped tellurite glasses sensitized by Yb 3+

Up-conversion luminescence characteristics under 975 nm excitation have been investigated with Tb 3+/Tm 3+/Yb 3+ triply doped tellurite glasses. Here, green (547 nm: 5D 4 → 7F 4) and red (660 nm: 5D 4 → 7F 2) up-conversion (UC) luminescence originating from Tb 3+ is observed strongly, because of the quadratic dependences of emission intensities on the excitation power. Especially, the UC luminescence was intensified violently with the energy transfer from the Tm 3+ ions involves in the Tb 3+ excitation. To the Tb 3+/Tm 3+/Yb 3+ triply doped glass system, a novel up-conversion mechanism is proposed as follows: the energy of 3G 4 level (Tm 3+) was transferred to 5D 4 (Tb 3+) and the 477-nm UC luminescence of Tm 3+ was nearly quenched.

Synthesis and two-photon absorption properties of 2,5-bis[4-(2-arylvinyl)phenyl]-1,3,4-oxadiazoles

Two symmetrical 2,5-bis[4-(2-arylvinyl)phenyl]-1,3,4-oxadiazoles that exhibit strong two-photon absorption and enhanced two-photon excited fluorescence were designed and synthesized based on “push-core-pull-core-push” molecules built from embedding electron-transporting 1,3,4-oxadiazole in aromatic conjugated system through Wittig–Horner reaction. Pumped by nanosecond laser at 800 nm, strong up-conversion emissions with the central wavelength at 507 nm (green) of 2,5-bis[4-(2- N, N-diphenylaminostyryl)phenyl]-1,3,4-oxadiazole and 475 nm (blue) of 2,5-bis[4-{2-(3- N-ethylcarbazolyl)vinyl}phenyl]-1,3,4-oxadiazole in the solution of CHCl 3 have been observed. Their two-photon absorption cross-sections obtained by nonlinear transmission method are 107 × 10 −48 cm 4 s photon −1 and 66 × 10 −48 cm 4 s photon −1. A very effective energy transfer from the excited terminal units to the π-conjugated bridging units of the 2,5-bis[4-(2-arylvinyl)phenyl]-1,3,4-oxadiazoles is the dominant contribution to the two-photon absorption.

Infrared-to-ultraviolet up-conversion luminescence of YF 3:Yb 3+, Tm 3+ microsheets

YF 3:Yb 3+,Tm 3+ microsheets were synthesized by a simple hydrothermal method. The sheets structure was characterized by X-ray diffraction, scanning electron microscopy and transmission electron microscopy. Strong ultraviolet and blue up-conversion emissions were observed at 978 nm. The intensity dependence of up-conversion emission on pump power was measured, which shows that the populations of the states 1 I 6, 1 D 2 and 1 G 4 may come from five-photon, four-photon and three-photon energy transfer up-conversion processes, respectively.

Optical parameters and upconversion fluorescence in Tm3+/Yb3+-doped alkali-barium-bismuth-tellurite glasses

Tm3+/Yb3+-doped alkali-barium-bismuth-tellurite (LKBBT) glasses have been fabricated and characterized. Density, refractive index, optical absorption, absorption and emission cross-sections of Yb3+, Judd–Ofelt parameters and spontaneous transition probabilities of Tm3+ have been measured and calculated, respectively. Intense blue three-photon upconversion fluorescence and near-infrared two-photon upconversion fluorescence were investigated under the excitation of a 980nm diode laser at room temperature. Wide infrared transmission window, high refractive index and strong blue three-photon upconversion emission of Tm3+ indicate that Tm3+/Yb3+ co-doped LKBBT glasses are promising upconversion optical and laser materials.

Intense blue upconversion fluorescence of Tm3+/Yb3+-codoped bismuth tellurite glasses

In this paper, Tm3+/Yb3+-codoped bismuth tellurite glasses with high refractive index have been synthesized. The refractive index of Tm3+/Yb3+-codoped bismuth tellurite glasses were measured by Metricon 2010 prism coupler at two wavelengths, and the values n1=2.0365 at 632.8nm and n2=1.9795 at 1550nm were obtained. The absorption spectra, fluorescence spectra and infrared transmittance spectra of this glass were measured and analyzed. Based on Judd-Ofelt theory, and intensity parameters Ωt(t=2，4 and 6) were obtained to be 3.90×10-20, 2.03×10-20 and 9.03×10-21cm2, respectively. Then the radiative transition probabilities, radiative lifetimes and fluorescence branching ratio were calculated. Intense blue three-photon upconversion fluorescence and near-infrared two-photon upconversion fluorescence were investigated under the excitation of 980nm diode laser at room temperature. Wide infrared transmission window, high refractive index and strong blue three-photon upconversion emission of Tm3+ indicate that Tm3+/Yb3+-codoped LKBBT glasses are promising upconversion optical and laser materials.

Crystallization and spectroscopic properties investigations of Er 3+ doped transparent glass ceramics containing CaF 2

Transparent oxyfluoride glass ceramics with composition of 45SiO 2–25Al 2O 3–5CaCO 3–10NaF–15CaF 2–0.5ErF 3 (in mol%) were developed through controlled crystallization of melt-quenched glass. Non-isothermal crystallization kinetics investigation showed that the average apparent activation energy E a and Avrami exponent n are about 283 kJ/mol and 2.22, respectively, indicating the crystallization a three dimensional crystal growth process controlled by the diffusion with a decreasing nucleation rate. X-ray diffraction (XRD) analysis and transmission electron microscopy (TEM) observation revealed the precipitation of CaF 2 crystallites sized about 15 nm among the glass matrix after heat-treatment at 650 °C for 2 h. For as-made glass, no upconversion signals were detected when excited with a 30 mW diode laser at 980 nm, while strong upconversion emissions at 545, 660 and 800 nm were obtained for transparent glass ceramic under similar excitation condition.

Upconversion properties of the Er 3+ doped 20GaF 3–15InF 3–20CdF 2–15ZnF 2–20PbF 2–10SnF 2 glasses

Upconversion properties of Er 3+ doped 20GaF 3–15InF 3–20CdF 2–15ZnF 2–20PbF 2–10SnF 2 (GICZPS) glasses under 761 nm excitation were studied by the absorption, emission, excitation and fluorescence lifetime spectrum at room temperature. Strong upconversion emissions at 408 nm and 545 nm were obtained at the same time. The intensity of violet emission at 408 nm is almost as strong as that of 545 nm. When Er 3+ content is 0.15 mol%, the emission peaks of 408 nm and 545 nm all exhibit their maximal intensity. The upconversion mechanism of the two emissions is two-photon process.

Effect of oxygen substitution by halide ions on structure, thermal stability and upconversion fluorescence in Er 3+/Yb 3+-codoped germanium–bismuth glasses

For the first time, effect of halide ions (F −, Cl −, Br −, and I −) introduction on structure, thermal stability, and upconversion fluorescence in Er 3+/Yb 3+-codoped oxide–halide germanium–bismuth glasses has been systematically investigated. The results show that halide ions modified germanium–bismuth glasses have lower maximum phonon energy and phonon density, worse thermal stability, longer measured lifetimes of 4I 11/2 level, and stronger upconversion emission than germanium–bismuth glass. All these results indicate that halide ions play an important role in the formation of glass network, and have an important influence on the upconversion luminescence. The possible upconversion mechanisms of Er 3+ ion are also evaluated.

Effects of heat treatment temperature on up-conversion luminescence properties of titania/γ-glycidoxypropyltrimethoxysilane composite thin films dispersed with neodymium oxalate nanoparticles

Neodymium (III) oxalate nanoparticles prepared by the microemulsion technique are dispersed in sol–gel titania/γ-glycidoxypropyltrimethoxysilane composite thin films. Up-conversion emission of the composite thin films heated at different heat treatment temperatures is studied. A relatively strong room-temperature violet up-conversion emission at 399 nm ( 4D 3/2→ 4I 13/2) is measured from the composite thin film heated at 100 °C upon excitation at a yellow light of 587 nm. In addition to this violet emission, an UV emission at 376 nm and a blue emission at 467 nm are also observed. With an increase of heat treatment temperature, except mentioned emissions above, a relatively weak emission at about 349 nm can be also observed from the thin films heated at 500 and 600 °C. The lifetime of the violet emission is measured. The mechanism of the up-conversion emission is proposed. Thermal gravimetric analysis and atomic force microscopy are also employed to characterize the effect of heat treatment temperature on up-conversion emission properties of the thin films.