Upconversion Excitation Spectra Research Articles

Simulating excited-state absorption spectra in upconverting lanthanide doped nanoparticles: KY3F10:Er3+

High-resolution absorption and laser-excited fluorescence studies of KY3F10:Er3+ core-only nanoparticles are presented. A total of 49 crystal-field energy levels, distributed amongst 13 multiplets of the Er3+ ion, have been deduced for the C4v point group symmetry centre in this material. A parametrized, single-electron crystal-field calculation provides an excellent approximation to the experimental data with optimized crystal fit parameters that are comparable to the bulk KY3F10:Er3+ crystal. Simulated spectra, based upon wavefunctions derived from the crystal-field calculations, unequivocally demonstrate that excited-state absorption is the predominant upconversion mechanism in this material – agreeing well with upconversion excitation spectra obtained for Yb3+ co-doped samples.

Upconversion Thermometry Using Yb3+/Er3+ Co-Doped KY3F10 Nanoparticles

We report high-sensitivity luminescence thermometry using Yb3+/Er3+ co-doped KY3F10 core and core–shell upconverting nanoparticles. The highest thermal sensitivities of 1.510 ± 0.015%·K–1 (300 K) and 1.245 ± 0.013%·K–1 (316 K) and temperature uncertainty of 0.11 K were achieved by tuning the excitation wavelength to 975 nm to be in-resonant with optical transitions of the Yb3+ ion. The high-resolution Yb3+ excitation spectra were recorded by observing the Er3+, 4S3/2, 4F9/2 → 4I15/2 upconversion fluorescence, with the highest fluorescence yield obtained at 10 254 cm–1 (975 nm) for both nanoparticles. This coincides with the ground-state absorption maximum at 297 K. However, at 10 K, the Yb3+ upconversion excitation spectra also exhibit excited-state absorption peaks. The Yb3+ absorption spectra for the core and core–shell nanoparticles are dominated by single-ion centers (of C4v symmetry). Resonant excitation of the core and core–shell nanoparticles is observed to yield a 5-fold enhancement in Er3+ upconversion fluorescence intensity in comparison to excitation at 980 nm, increasing the fluorescence intensity ratio and the thermal sensitivity of a KY3F10 nanothermometer operating at the physiological temperatures.

A comparison of the Yb3+ absorption and upconversion excitation spectra for both the cubic and hexagonal phases of NaYF4:Yb3+/Er3+ nanoparticles

We report on studies of the Yb3+ ion absorption in Er3+ co-doped cubic and hexagonal phase NaYF4 upconverting nanoparticles using high-resolution absorption measurements. The Yb3+ absorption spectra have intense maxima at 10266.1 cm−1 and 10237.0 cm−1 for the cubic and hexagonal phases respectively, which is far from the most commonly used laser diode wavelength. Resonant excitation of these absorption maxima yields a ~40% (cubic) and ~34% (hexagonal) enhancement of the 2H11/2, 4S3/2 and 4F9/2 visible upconversion fluorescence. The hexagonal phase material exhibits Er3+ upconversion fluorescence which is a factor of 104 brighter than that obtained from the cubic phase nanoparticles, irrespective of their sizes, morphologies and Ln3+ ion distribution. The upconversion excitation spectra show preliminary evidence of excited state absorption features when monitoring 4F9/2 fluorescence for the hexagonal phase material.

Absorption spectra, defect site distribution and upconversion excitation spectra of CaF2/SrF2/BaF2:Yb3+:Er3+ nanoparticles

We report studies of the Yb$^{3+}$ site distribution in Er$^{3+}$ co-doped upconverting alkaline earth fluoride nanoparticles using high-resolution absorption measurements. Similar to bulk crystals, Yb$^{3+}$ single ion cubic (O$_h$), and preferentially formed clusters are the dominant centres for moderate dopant concentrations. At higher concentrations, and for larger particle sizes, a minority C$_{4v}$(F$^-$) centre is also observed. Furthermore, the behaviour of Yb$^{3+}$ cluster centres, whose primary absorption band is located around 10205 cm$^{-1}$ (in near resonance with 980 nm laser diodes) was studied by tuning the metal cation in the host lattice from Ca$^{2+}{\rightarrow}$Sr$^{2+}{\rightarrow}$Ba$^{2+}$. For co-doped materials, with heterogeneous cluster centres, Er$^{3+}$ upconversion fluorescence was observed upon selective excitation of Yb$^{3+}$, resulting in strong visible emission from $^4$H$_{11/2}$, $^4$S$_{3/2}$ and $^4$F$_{9/2}$ multiplets. By monitoring the Er$^{3+}$ $^4$S$_{3/2}{\rightarrow}^4$I$_{15/2}$ (540 nm) fluorescence, whilst scanning a laser through the wavelength dependent Yb3+ absorption, we obtain an excitation spectrum for these heterogeneous cluster centres. It is demonstrated that the group of Yb$^{3+}$ ions residing near an Er$^{3+}$ ion represent a small subset of the overall Yb$^{3+}$ ensemble and therefore a linear absorption measurement is not necessarily a good indication of the optimum laser pump wavelength.

Up-conversion luminescence of Er(Yb)-CeO 2 : Status and new results

Abstract We investigate the down- and up-conversion properties of Er (0.3, 1 and 3%)-CeO2 and Er(1%)Yb(20%)-CeO2 nanoparticles by use of ns pulsed monochromatic excitation. The emission spectra were recorded in the visible to near-infrared range (500–1100 nm) under ultraviolet, visible (490 and 650 nm) and near-infrared (790, 971/977 and 1470 nm) up-conversion excitations as well as X-ray excitation. The structural properties were characterized by X-ray diffraction, Raman, Diffuse Reflectance UV/Vis and Diffuse Reflectance Fourier Transform Infrared spectroscopies. The role of CeO2 charge transfer band as a level selective antenna sensitizer, the dopant induced oxygen vacancies and the effect of Er concentration on the overall emission properties are highlighted. The mechanisms involved in the up-conversion emission in Er-CeO2 and Er,Yb-CeO2 are analysed in terms of up-conversion excitation spectra, up-conversion emission decays and evolution of the red to green emission ratio with Er concentration and delay after the laser pulse. Our findings are also discussed in the context of a comprehensive literature survey regarding the actual stage of research on the luminescence of Er and Er,Yb doped CeO2 and their possible applications.

Analysis of the upconversion processes of Nd3+ ions in transparent YAG ceramics

Optical properties of Nd3+ ions in YAG transparent ceramics have been analysed. The samples were prepared by a high temperature (1650 and 1680°C) sintering followed by hot isostatic pressing (HIP) at 1650 or 1700°C in order to obtain a well-homogeneous diffusion of the ions and functional transparency. The emission and luminescence decay curves from the 4F3/2 metastable laser level of these samples are very similar to the ones obtained on crystal samples grown with the Czochralski method. However, excitation upconversion spectra obtained detecting at 590nm for the transparent ceramic samples present important differences compared to the bulk YAG crystal, which can be explained by a change in the upconversion mechanism involved and the different arrangements of the Nd3+ ions in the YAG matrix. The analysis of the upconversion excitation spectra is shown to be a good method to detect the differences between the positions occupied by the Nd3+ ions in different matrices.

Ultraviolet and visible upconversion luminescence in Nd3+-doped oxyfluoride glasses and glass ceramics obtained by different preparation methods

Ultraviolet and visible upconversion emissions under infrared excitation have been obtained and compared in Nd3+-doped oxyfluoride glasses and glass ceramics prepared by different methods. The mechanisms involved in such processes have been analyzed. A spectroscopy study comparing absorption and upconversion excitation spectra has been carried out in order to discern in each case the mechanism involved in the origin of the upconversion emissions, i.e., two- or three-photon involved excited state absorption or energy transfer processes. The shape of the absorption and emission spectra and the relative upconversion efficiencies have been compared and explained taking into account the final distribution of the luminescent ions in the glassy and nanocrystalline phases.

The study of two-color excitation upconversion of Pr(0.5)Yb(3):ZBLAN

The excited state absorption upconversion of Pr(0.5)Yb(3):ZBLAN glass material, under two-color excitation of the 960 nm semiconductor laser and the Xe lamp light simultaneously, is reported in this article. It was found that the upconversion emission spectra of 480.1, 519.0, 601.9 and 631.8 nm coincide with the common emission spectra. Meanwhile, the upconversion-excitation spectrum has three obvious peaks under two-color excitation, and they respectively correspond to the 856.0 nm upconversion excitation transition [1G4(Pr3+)→1I6(Pr3+) and 1G4(Pr3+)→3P1(Pr3+)], the 789.0 nm upconversion excitation transition 1G4(Pr3+)→3P2(Pr3+), and the 803.7 nm upconversion excitation transition 3H6(Pr3+)→1D2(Pr3+). The upconversion excitation transition 1G4(Pr3+)→1I6(Pr3+) is strong because its oscillator strength f = 23.040×10−6 is large, which results in a large peak appearing in the upconversion excitation spectrum. That is just the new interesting two-color excitation upconversion luminescence phenomenon of Pr(0.5)Yb(3):ZBLAN induced by one laser and one continuous normal light simultaneously.

Yb3+-sensitized visibleNi2+photon upconversion in codopedCsCdBr3andCsMgBr3

Near-infrared excitation of ${\mathrm{Yb}}^{3+}\phantom{\rule{0.2em}{0ex}}^{2}F_{7∕2}\ensuremath{\rightarrow}^{2}F_{5∕2}$ at $10\phantom{\rule{0.2em}{0ex}}600\phantom{\rule{0.3em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}1}$ in the linear chain $\mathrm{Cs}\mathrm{M}{\mathrm{Br}}_{3}:{\mathrm{Ni}}^{2+},{\mathrm{Yb}}^{3+}\phantom{\rule{0.2em}{0ex}}(M=\mathrm{Cd},\mathrm{Mg})$ structure leads to green luminescence from ${\mathrm{Yb}}^{3+}$ pairs and red ${\mathrm{Ni}}^{2+}$ upconversion luminescence at cryogenic temperatures. The broad red upconversion luminescence is assigned to the $^{1}T_{2g}\ensuremath{\rightarrow}^{3}A_{2g}$ transition of ${\mathrm{Ni}}^{2+}$. The upconversion excitation spectrum indicates that the active mechanism in these systems involves both ${\mathrm{Yb}}^{3+}$ and ${\mathrm{Ni}}^{2+}$ ions. Lifetime and power dependence data allow one to identify a ground-state-absorption (GSA) energy-transfer upconversion (ETU) as the underlying upconversion mechanism for the ${\mathrm{Yb}}^{3+}\text{\ensuremath{-}}{\mathrm{Ni}}^{2+}$ system in doubly doped $\mathrm{Cs}\mathrm{Cd}{\mathrm{Br}}_{3}$ and $\mathrm{Cs}\mathrm{Mg}{\mathrm{Br}}_{3}$. A less efficient single-ion GSA excited-state-absorption (ESA) process within ${\mathrm{Ni}}^{2+}$ is also observed in the title compounds. However, whereas the GSA/ESA process requires an excitation energy above $11\phantom{\rule{0.2em}{0ex}}200\phantom{\rule{0.3em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}1}$, it is possible to sensitize the ${\mathrm{Ni}}^{2+}$ upconversion via ${\mathrm{Yb}}^{3+}$ excitation at energies around $10\phantom{\rule{0.2em}{0ex}}200\phantom{\rule{0.3em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}1}$ and around $10\phantom{\rule{0.2em}{0ex}}600\phantom{\rule{0.3em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}1}$ in $\mathrm{Cs}\mathrm{Cd}{\mathrm{Br}}_{3}$ and $\mathrm{Cs}\mathrm{Mg}{\mathrm{Br}}_{3}$. It is shown that only those ${\mathrm{Ni}}^{2+}$ ions neighboring to ${\mathrm{Yb}}^{3+}$ ions are relevant for the upconversion induced by ${\mathrm{Yb}}^{3+}$ excitation.

The excited state upconversion of Pr(0.5):ZBLAN under two-color excitation*

This paper reports the excited-state upconversion of Pr(0.5):ZBLAN glass under two-color excitation. It is found that the fluorescence of upconversion-emiss ion spectrum is the same as that of common-emission spectrum. It is found also that there are three obvious peaks on upconversionexcitation spectrum under twocolor excitation, which corresponds to the 788.5nm 1G4→3P2,850.5nm 1G4→1I6,and 805.0nm 3H6→1D2 excited state absorpt ion transitions res pectively. The large 850.5nm peak of upconversion-excitation spectrum results from the large 1G4(Pr3+ )→1I6(Pr3+) (Pr3+) oscil lator strength f=23.04×10-6. It illustrates the excited state absorp tion upconve rsion from 1G4 level, especially the 1G4(Pr3+)→1I6(Pr3+) upconversion process is large. It results in the upcon version luminescence of Pr(0.5):ZBLAN under two-color excitation.

Sharp2Eupconversion luminescence ofCr3+inY3Ga5O12codoped withCr3+andYb3+

We report on upconversion luminescence in ${\mathrm{Y}}_{3}{\mathrm{Ga}}_{5}{\mathrm{O}}_{12}$ codoped with ${\mathrm{Cr}}^{3+}$ and ${\mathrm{Yb}}^{3+}.$ This is, to our knowledge, the first upconversion process directly involving ${\mathrm{Cr}}^{3+}.$ At low temperature excitation around 10 314 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$ leads to relatively strong red luminescence in the title compound. The sharp upconversion luminescence around 14 300 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$ is identified as the ${}^{2}{E}^{4}{A}_{2}$ transition of ${\mathrm{Cr}}^{3+}.$ The upconversion excitation spectrum follows the ${\mathrm{Yb}}^{3+}$ ${}^{2}{\stackrel{\ensuremath{\rightarrow}}{{F}_{7/2}}}^{2}{F}_{5/2}$ absorptions in the range 11 200--10 315 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$. From transient measurements the upconversion mechanism is found to be dominated by an energy transfer step: Two excited ${\mathrm{Yb}}^{3+}$ ions simultaneously transfer their excitation energy to the ${\mathrm{Cr}}^{3+}$ ion. In ${\mathrm{Y}}_{3}{\mathrm{Ga}}_{5}{\mathrm{O}}_{12}:2%$ ${\mathrm{Cr}}^{3+},$ 1% ${\mathrm{Yb}}^{3+}$ the efficiency of the process at 10 K and for 150 mW laser power is 6% and decreases with increasing temperature due to intrinsic loss mechanisms of the system.

Luminescence Upconversion Under High Pressure in Ni 2+ Doped CsCdCl 3

The near-infrared to visible upconversion properties of Ni 2+ doped CsCdCl 3 are studied as a function of hydrostatic pressure. At 15 K and ambient pressure, near-infrared excitation of Ni 2+ around 810 nm leads to upconversion luminescence centered around 610 nm. Due to the increase of the ligand field strength with increasing pressure, the emission band moves to higher energies with a rate of 19 cm m 1 /kbar, and at 46 kbar it is centered around 585 nm. Thus the upconversion luminescence undergoes a color change from red to yellow in the 1 bar-46 kbar pressure range. The 15 K pressure-dependent upconversion excitation spectra reveal a slight red-shift of m 4 cm m 1 /kbar of the upconversion relevant 3 T 2g M 1 T 2g excited state absorption (ESA) transition, and this is related to a reduction of the Racah B and C parameters, caused by an increasing degree of covalency in the Ni 2+ -Cl m interaction towards higher pressures. Thus, with upconversion luminescence excitation spectroscopy we can obtain information about the pressure-dependence of an ESA transition. The pressure-induced intensity redistributions within this excitation spectrum are indicative of an increasing spectral overlap of 3 T 2g M 1 T 2g ESA with 3 A 2g M 3 T 1g ground state absorption, potentially leading to more efficient upconversion at higher pressures than at ambient pressure.

Up-conversion excitation of sharp Cr 3+2E emission in YGG and YAG codoped with Cr 3+ and Yb 3+

The 2E→ 4A 2 emission of Cr 3+ in crystals and glasses is of great importance in science and technology. We found a new excitation mode for this emission in the garnets YGG and YAG codoped with Cr 3+ and Yb 3+. It is based on an up-conversion mechanism using 2F 5/2 of Yb 3+ as an intermediate state. Excitation of the Yb 3+ in the near infrared around 1000 nm leads to visible Cr 3+ 2E→ 4A 2 emission around 700 nm at low temperatures. The up-conversion luminescence intensity shows a strong temperature dependence due to an intrinsic loss mechanism. The up-conversion excitation spectra follow the Yb 3+ 2F 7/2→ 2F 5/2 absorptions. From its time dependence the up-conversion mechanism is found to be dominated by an energy transfer step: Two excited Yb 3+ ions simultaneously transfer their 2F 5/2 excitation to Cr 3+.

Luminescence spectroscopy and NIR to VIS upconversion of Cs2GeF6: 2% Re4+

We present and analyse high-resolution absorption, luminescence and upconversion-luminescence spectra of Cs2GeF6: 2% Re4+. The crystals of Cs2GeF6: 2% Re4+ were grown from solution. Upon excitation around 11 000 cm−1 in the near infrared, visible upconversion luminescence around 17 000 cm−1 is observed. On increasing the temperature from 15 K to room temperature the integrated upconversion luminescence intensity decreases to 2%. This is attributed to the decreasing absorption cross-section at the monochromatic laser-excitation energy. The upconversion excitation spectra and the results obtained from time-dependent measurements indicate a dominant energy-transfer upconversion mechanism.

Disordered laser gain media: Er 3+ doped CaGdAlO 4 and Ca 3Ga 2Ge 4O 14

We report on the optical spectroscopy of trivalent erbium ions doped into compositionally disordered oxide host materials, CaGdAlO 4 and Ca 3Ga 2Ge 3O 14. In either material, averaged spectral linewidths of close to 40 cm −1 are measured to be concentration independent up to 5 mol% of the dopant ion. For laser excitation resonant with the 4I 15/2→ 4F 9/2 and 4I 13/2→ 4F 5/2 and 4F 3/2 transitions, intense blue and green upconversion fluorescence is observed. Dips in the upconversion excitation spectra are attributable to radiative energy transfer (or self-absorption) which is known to enhance energy storage and upconversion.

New photon upconversion processes in Yb 3+ doped CsMnCl 3 and RbMnCl 3

Excitation around 980 nm and 935 nm leads to visible luminescence in the title compounds below 100 K. The broad luminescence band centered around 690 nm and 630 nm in Yb 3+ doped CsMnCl 3 and RbMnCl 3, respectively, is identified as a 4 T 1→ 6 A 1 transition on Mn 2+. The upconversion excitation spectrum follows the 2 F 7/2→ 2 F 5/2 absorptions around 980 nm and 935 nm. Excitation with 10 ns pulses induces instantaneous upconversion luminescence, indicating that no energy transfer is involved in the process. The most likely mechanism for this new type of upconversion process is based on exchange interactions between neighboring Yb 3+ and Mn 2+ ions. In a dimer picture the intermediate excitation is mainly, but not exclusively localized on Yb 3+, whereas the upper emitting state is mainly but not exclusively localized on Mn 2+.

Polarized laser spectroscopy and crystal-field analysis of Er3+ doped CaGdAlO4

A single Er3+ centre in CaGdAlO4:Er3+ has been identified to have C4v symmetry from polarized laser selective excitation. This is consistent with isovalent substitution of the Er3+ ions for host crystal Gd3+ ions. Using both optical and infrared absorption and polarized laser excited fluorescence, 59 crystal-field energy levels and their wavefunction symmetries have been identified and used to perform comprehensive single electron crystal-field analyses for the Er3+ ion centre. For excitation of the 4F9/2 multiplet, blue and green upconversion fluorescence is observed. Self-absorption dips recorded in upconversion excitation spectra are indicative of the presence of radiative energy transfer processes.

Infrared-to-blue-wavelength upconversion in thin film grown by liquid phase epitaxy

Blue emission at 486 nm corresponding to the transition in (GGG) thin epitaxial film was generated after excitation with infra-red radiation at around 890 nm. The upconversion mechanism was shown to be excited-state absorption from the multiplet. The spectroscopic properties of the state of in GGG were also studied. The emission spectra of bulk crystals and thin film are centred at , and the measured lifetime is about at room temperature. Blue-wavelength upconversion excitation spectra and direct infra-red excitation spectra allowed us to determine the Stark energy levels in the and multiplets.

Room temperature blue upconverted luminescence via photon avalanche pumping in Cs2NaGdCl6:Tm3+

Experimental results are presented to show that the intense, blue upconverted luminescence observed from Cs2NaGdCl6 doped with 6,10 and 15 at.% Tm3+, when excited by a cw laser near 650 nm at room temperature, is due to a photon avalanche process. A slow rise of the upconverted blue-emission intensity, over several seconds, takes place near the threshold power level. Emission is not only observed from the1G4 term manifold, but also from1D2. The well-resolved upconversion excitation spectrum indicates clearly that excited-state absorption to1G4 takes place from the3F4 multiplet term of Tm3+.