Energy Transfer Upconversion Research Articles

Energy transfer and color tunable up-conversion luminescence in PrF3 and YbF3 co-doped SrF2 transparent ceramics

Near-infrared pumped up-conversion luminescent PrF3 and YbF3 co-doped SrF2 ceramics were fabricated by the hot-pressing sintering technique, and the pellets were transparent with a primrose yellow appearance. The influence of YbF3 co-doping levels on the optical qualities and microstructures of ceramics was investigated. We identified the mechanisms to realize up-conversion luminescence in the visible range from 3P0,1 levels (Pr3+) under near-infrared wavelength pumping sources other than the near ultraviolet to blue region photons. Yb3+ ions inducing a broad and intense absorption band at the 900–1050 nm region, and the absorption coefficient and cross-section at 980 nm are 7.57 cm−1 and 4.19 × 10−21 cm2 in the ceramic co-doped with 15 wt% YbF3, respectively. The intense up-conversion luminescence bands at 480, 520, 540, and 600 nm under 980 nm excitation were attributed to 3P0→3H4, 3P1→3H5, 3P0→3H5 and 1D2→3H4 transitions of Pr3+ ions, respectively.

Effect of Yb3+/Er3+ co-doping on the emission properties of fluoroindate glass and glass optical fiber

In this study, a comprehensive analysis of emission in erbium-doped and erbium and ytterbium co-doped fluoroindate glasses has been presented. The luminescence of the erbium transitions and the effect of ytterbium co-doping under 488, 808 and 976 nm laser excitation have been discussed. Optimization of rare-earth (RE) ions doping concentration and the energy transfer processes related to the sensibilization effect in Er3+/Yb3+ co-doped fluoroindate glasses focusing on the reciprocal distribution of radiative transitions, energy transfer parameters, and lifetimes have been analyzed. The luminescence consists of several bands in the visible (525, 546 and 660 nm) and the infrared (1550 and 2700 nm) spectral regions that correspond to characteristic radiative energy transitions within the erbium ions. In glasses co-doped with the Er3+/Yb3+ system, an augmentation in the emission intensity was observed in the visible and at 1550 nm, while a decrease was observed in the 2700 nm infrared band. The increase of the Yb3+: 2F5/2 lifetime under 488, 808 and 976 nm excitation showed significant Er3+: 4I11/2 → Yb3+: 2F5/2 back energy transfer. Based on the analysis of the available literature, it can be concluded that energy transfer upconversion and cooperative energy upconversion play a significant role in modulating luminescence intensity values within the examined emission bands. This effect is likely enhanced due to the incorporation in a low phonon energy glass matrix. As a result of the above optimization, a glass optical fiber co-doped with 0.8 YbF3/1.4 ErF3 (in mol%) was drawn and characterized, showing a strong emission at 2.77 μm. The optimized Er3+/Yb3+ co-doped fluoroindate glass and glass optical fiber confirmed their ability to be used in the visible and near-infrared spectral regions as efficient optical fiber sources.

Upconversion luminescence enhancement and color modulation in Yb3+/Er3+/Ln3+ (Ln = Tm, Ho) tri-doped YF3 microrods

Intelligent regulation of energy transfer process among different rare earth ions doped in the matrix is an effective strategy to realize high-performance upconversion (UC) luminescence. Based on this, wheat ears like Yb3+/Er3+/(Tm3+, Ho3+) triple doped YF3 microrods were fabricated via hydrothermal method, and the morphology, crystal structure, UC luminescence performance dependent on Tm3+/Ho3+ doping concentrations were studied. By comparing with the Yb3+, Er3+ co-doped YF3 microrods, the UC luminescence intensity is enhanced in Yb3+/Er3+/(Tm3+, Ho3+) triple doped YF3 samples due to the cross relaxation processes between Er3+ and Tm3+/Ho3+. Moreover, red emission is enhanced more significantly than green emission in YF3: Yb3+, Er3+, Tm3+, which is contrary to that in YF3: Yb3+, Er3+, Ho3+. The possible energy transfer upconversion mechanism involved is discussed in detail. Meanwhile, an adjustable emission color is easy to achieve via altering the doped Er3+/Tm3+/Ho3+ ion concentration. These studies on the UC luminescence enhancement mechanism of Yb3+/Er3+/(Tm3+, Ho3+) triple doped YF3 microrods are expected to provide a reference for the development of high-efficiency luminescent materials.

Population Control of Upconversion Energy Transfer for Stimulation Emission Depletion Nanoscopy.

Upconverting stimulated emission depletion microscopy (U-STED) is emerging as an effective approach for super-resolution imaging due to its significantly low depletion power and its ability to surpass the limitations of the square-root law and achieve higher resolution. Though the compelling performance, a trade-off between the spatial resolution and imaging quality in U-STED has been recognized in restricting the usability due to the low excitation power drove high depletion efficiency. Moreover, it is a burden to search for the right power relying on trial and error as the underpinning mechanism is unknown. Here, a method is proposed that can easily predict the ideal excitation power for high depletion efficiency with the assistance of the non-saturate excitation based on the dynamic cross-relaxation (CR) energy transfer of upconversion nanoparticles. This allows the authors to employ the rate equation model to simulate the populations of each relevant energy state of lanthanides and predict the ideal excitation power for high depletion efficiency. The authors demonstrate that the resolution of STED with the assistance of nonsaturated confocal super-resolution results can easily achieve the highest resolution of sub-40nm, 1/24th of the excitation wavelengths. The finding on the CR effect provides opportunities for population control in realizing low-power high-resolution nanoscopy.

Seeking Brightness in Molecular Erbium-Based Light Upconversion.

Whereas dye-sensitized lanthanide-doped nanoparticles represent an unquestionable advance for pushing linear near-infrared (NIR) to visible-light upconversion within the frame of applications, analogous improvements are difficult to mimic for related but intramolecular processes induced at the molecular level in coordination complexes. Major difficulties arise from the cationic nature of the target cyanine-containing sensitizers (S), which drastically limits their thermodynamic affinities for catching the lanthanide activators (A) required for performing linear light upconversion. In this context, the rare previous design of stable dye-containing molecular SA light-upconverters required large S···A distances at the cost of the operation of only poorly efficient intramolecular S → A energy transfers and global sensitization. With the synthesis of the compact ligand [L2]+, we exploit here the benefit of using a single sulfur connector between the dye and the binding unit for counterbalancing the drastic electrostatic penalty which is expected to prevent metal complexation. Quantitative amounts of nine-coordinate [L2Er(hfac)3]+ molecular adducts could be finally prepared in solution at millimolar concentrations, while the S···A distance has been reduced by 40% to reach circa 0.7 nm. Detailed photophysical studies demonstrate the operation of a three times improved energy transfer upconversion (ETU) mechanism for molecular [L2Er(hfac)3]+ in acetonitrile at room temperature, thanks to the boosted heavy atom effect operating in the close cyanine/Er pair. NIR excitation at 801 nm can thus be upconverted into visible light (525-545 nm) with an unprecedented brightness of Bup(801 nm) = 2.0(1) × 10-3 M-1·cm-1 for a molecular lanthanide complex.

Frequency-Domain Method for Characterization of Upconversion Luminescence Kinetics.

The frequency-domain (FD) method provides an alternative to the commonly used time-domain (TD) approach in characterizing the luminescence kinetics of luminophores, with its own strengths, e.g., the capability to decouple multiple lifetime components with higher reliability and accuracy. While extensively explored for characterizing luminophores with down-shifted emission, this method has not been investigated for studying nonlinear luminescent materials such as lanthanide-doped upconversion nanoparticles (UCNPs), featuring more complicated kinetics. In this work, employing a simplified rate-equation model representing a standard two-photon energy-transfer upconversion process, we thoroughly analyzed the response of the luminescence of UCNPs in the FD method. We found that the FD method can potentially obtain from a single experiment the effective decay rates of three critical energy states of the sensitizer/activator ions involved in the upconversion process. The validity of the FD method is demonstrated by experimental data, agreeing reasonably well with the results obtained by TD methods.

Up-conversion and downconversion studies of Nd3+ doped borophosphate glasses

Neodymium doped borophosphate glasses have been synthesizsed by melt quenching technique to investigate their luminescence properties. The increase in density and decrease in molar volume with increasing concentration of Nd2O3 (0.1 mol% to 0.5 mol%) established the participation of Nd3+ in the glass structure. Non-crystalline nature of prepared glasses is confirmed by the absence of sharp peaks in X-ray diffraction spectra. The various structural units due to B2O3, P2O5, and PbO were identified by Fourier transform infrared spectroscopy. Ultraviolet visible absorption spectroscopy showed various absorption peaks/bands at 742 nm (4F7/2+4S3/2), 684 nm (4F9/2), 626 nm (2H11/2), 581 nm (4G5/2+2G7/2), 523 nm (4G7/2+4G9/2+ 2K13/2), 431 nm (2D5/2+2P1/2), 358 nm (4D3/2+4D5/2), 338 nm (2I11/2), and 315 (4D7/2+2I13/2+2L15/2). The optical parameters, namely indirect band gap, molar refractivity, molar polarizability, electronic polarizability and dielectric constant showed linear trend with increasing concentration of Nd2O3. Judd-Ofelt parameters followed Ω6> Ω4> Ω2 trend. The experimental and calculated oscillator strength for 584 nm is highest among all transitions because it is hypersensitive in nature. Upon 806 nm excitation, four visible peaks at 489 nm, 540 nm, 605 nm and 671 nm were observed. Excited state absorption up-conversion and energy transfer up-conversion mechanisms were responsible for visible up-conversion. At 338 nm, ultraviolet energy is downconverted to 448 nm, 529 nm, 591 nm. Commission International de I'Eclairage (CIE) chromaticity coordinates were evaluated from the up-conversion emission spectra and the coordinates lie in green region.

Boosting Photo Upconversion in Electropolymerised Thin Film with Yb/Er Complexes

AbstractUpconversion luminescence (UCL) in organometallic complexes has attracted great interest in photovoltaics and biological applications due to their fascinating energy transfer mechanism from low‐energy photon to high‐energy photon. However, photon‐upconversion operating in a single discrete entity remains a challenge caused by low‐absorption cross section of the luminescent lanthanide element. Here, a novel upconversion system is reported combining Yb (Ytterbium) sensitizers and Er (Erbium) activators in the film by electropolymerization, which leads to excited‐state absorption (ESA) and energy transfer upconversion (ETU) processes. For the first time, the UCL has been achieved in the thin films upon near‐infrared laser irradiation, and the upconversion intensity exhibits up to 30‐fold enhancement with the variation of Yb/Er ratio.

Generalised analytical model of the transition power densities of the upconversion luminescence and quantum yield.

The quantum yield (QY) evaluation of upconverting nanoparticles (UCNPs) is an essential step in the characterisation of such materials. The QY of UCNPs is governed by competing mechanisms of populating and depopulating the electronic energy levels involved in the upconversion (UC), namely linear decay rates and energy transfer rates. As a consequence, at low excitation, the QY excitation power density (ρ) dependence obeys the power law ρn-1, where n represents the number of absorbed photons required for the emission of a single upconverted photon and determines the order of the energy transfer upconversion (ETU) process. At high power densities, the QY transits to a saturation level independent of the ETU process and the number of excitation photons, as a result of an anomalous power density dependence present in UCNPs. Despite the importance of this non-linear process for several applications (e.g., living tissue imaging and super-resolution-microscopy), little has been reported in the literature regarding theoretical studies to describe the UC QY, especially for ETUs with order higher than two. Therefore, this work presents a simple general analytical model, which introduces the concept of the transition power density points and QY saturation to characterise the QY of an arbitrary ETU process. The transition power density points determine where the power density dependence of the QY and the UC luminescence changes. The results provided in this paper from fitting the model to experimental QY data of a Yb-Tm codoped β-UCNP for 804 nm and 474 nm emissions (ETU2 and ETU3 processes, respectively) exemplify the application of the model. The common transition points found for both processes were compared to each other showing strong agreement with theory, as well as, compared to previous reports when possible.

Universal Emission Characteristics of Upconverting Nanoparticles Revealed by Single-Particle Spectroscopy

Upconverting nanoparticles (UCNPs) have been extensively investigated for nanophotonics and biomedical applications. However, establishing a unified view of their emission characteristics to elucidate the underlying photophysics and expand the application fields of these materials is a great challenge due to their sophisticated internal energy transfer and lack of standardized single-particle spectroscopy (SPS) platform. Here, we present an SPS technique called multiband single-particle irradiance-dependent imaging (multiband SPIDI). We demonstrate that the emission characteristics of Yb3+,Tm3+-doped UCNPs are universal for three emission bands over a wide range of irradiance and dependent on the Tm3+ doping concentration, indicating that the number of emitted photons of each band is proportional to the number of activator ions and is dependent on the number of absorbed photons and the activator interionic distance. We also suggest a cooperative energy transfer upconversion (CETU) mechanism for transition to a higher-energy state through photon accumulation. For a single UCNP, the emission at 800 nm is detectable at an ultralow irradiance of 4.9 W cm-2; moreover, that at 450 nm is measurable at 98 W cm-2, based on the optimal concentration. These findings based on the multiband SPIDI platform can provide insights into the interionic energy transfer by studying irradiance-dependent steady-state dynamics to achieve brighter UCNPs and their broader applications.

Highly Efficient Near-Infrared Photoinduced Electron/Energy Transfer-Reversible Addition–Fragmentation Chain Transfer Polymerization via the Energy Transfer Upconversion Mechanism

Near-infrared (NIR) light-mediated polymerization has been of particular interest owing to the deep penetration into opaque materials, giving rise to great potential for biomedical applications and solar photochemistry. Photoinduced electron/energy transfer-reversible addition–fragmentation chain transfer (PET-RAFT) polymerization presented unprecedented spatiotemporal control over the controlled radical polymerization process. Herein, we greatly extended the NIR region up to 980 nm by introducing rationally designed upconversion nanocrystals with low toxicity and resistance to photobleaching into PET-RAFT polymerization. Well-defined polymers with predictable molecular weight and narrow dispersity were prepared within a few hours by 980 nm NIR light-regulated PET-RAFT polymerization via the energy transfer upconversion mechanism. The livingness feature of this photopolymerization was confirmed by polymerization kinetics, chain extension experiments, and multiple controlled “on–off” light switching cycles. Furthermore, the polymerizations could be successfully performed using different monomers, in the presence of several visible light-proof barriers (i.e., pork/chicken skin) and even under aerobic conditions, demonstrating the multifold advantages of our approach.

Quantitatively identifying the upconversion luminescence mechanisms of Er3+:NaYF4 nanocrystals in aluminosilicate glass ceramics under femtosecond laser field

Upconversion luminescence of lanthanide ion doped nanocrystals under ultrashort laser pulse excitation can find significant applications in areas like super-resolution nonlinear microscopic imaging and attracts increasing attention. Though major excitation mechanisms, such as excited state absorption (ESA), energy transfer upconversion (ETU) and multi-photon absorption (MPA), have been analyzed and discussed intensively, quantitative differentiation of their respective contributions with convincing experimental proof has seldom been reported however. Here we report experimental demonstration of a simple but effective way to quantitatively identify simultaneous MPA from other mechanisms like ESA and ETU involved in the Er3+ doped NaYF4 nanocrystals in aluminosilicate glass ceramics under femtosecond laser field excitation. Comparative studies using laser pulses of the same spectral bandwidth but different time duration or repetition rate are performed and convincing experimental evidences for their respective contribution weights are obtained. The dependence of the MPA excitation efficiency on the spectral bandwidth of the femtosecond laser pulse is also explored for maximizing the upconversion luminescence yield. And predictions from a theoretical model agree well with experimental observations.

Laser-Induced Heating in GdVO4: Yb3+/Er3+ Nanocrystals for Thermometry

Photoluminescent temperature sensors based on gadolinium orthovanadate (GdVO4) doped with 10% ytterbium and 2% erbium are developed and dispersed in different media (lubricant fluid, sol–gel glass, and PDMS) to evaluate the best conditions for temperature measurement. Two excitation modes are considered: (i) visible excitation by a downshifting (DS) process or (ii) NIR excitation by energy transfer upconversion (UC) between Yb and Er. The luminescence intensity ratio (LIR) of the thermally coupled Er3+ emission peaks varies linearly with temperature in the range of 25–300 °C, and this variation is reversible. The impact of the laser power density on thermometry via the UC process that has been verified with GdVO4: Yb3+/Er3+ powders and with its different dilutions (low and high concentration) shows that the LIR is highly dependent on the laser source intensity, the environmental temperature, and the dispersed medium. When GdVO4: Yb3+/Er3+ powders are dispersed at high concentration, high laser power density leads to significant laser-induced thermal heating. However, at low concentration, this laser thermal effect is no longer influenced by the laser intensity. In this paper, we propose a method to directly measure the laser-induced heating temperature and to correct the error caused by this effect on temperature measurement. According to these results, GdVO4: Yb3+/Er3+ upconversion nanoparticles can be applied for temperature sensing even if the laser-induced thermal effect occurs in the system.

Charging storage phosphors using a white flashlight via the upconversion approach

As an emerging approach to charge storage phosphors, upconversion charging (UCC) is attracting increased attention owing to its fundamental and practical perspectives. Despite the potential, further development of the UCC technology is restricted by the limited types of excitation light sources. Here, we use a white flashlight as excitation to investigate the UCC performance of storage phosphors. We demonstrate, as an example, that a Y3Al2Ga3O12:Pr3+ phosphor exhibits long-lasting emissions in the ultraviolet and visible regions after intense illumination from the flashlight. Thermoluminescence investigations reveal that both excited-state absorption and energy-transfer upconversion are involved in the UCC process. Based on the luminescence performance of the white-light charged phosphor, a conceptual thermometry approach is introduced, which can remotely sense the local temperature by monitoring the afterglow intensity ratio. Considering the wide use of flashlight, such a white-light excitability and the associated glow emission may potentially revolutionize the way to utilize storage phosphors.

White up-conversion La2Mo2O9:Yb3+, Ho3+, Tm3+ phosphors based on dual luminescence centers for high-sensitive optical thermometry

In this paper, the La2Mo2O9:Yb3+, Ho3+, Tm3+ phosphors are successfully synthesized through simple solid-state method. The white up-conversion luminescence is realized by appropriately varying the co-doped concentrations of Ho3+, Tm3+. The up-conversion luminescence characteristics and energy transfer processes of La2Mo2O9:Yb3+, Ho3+, Tm3+ are specifically analyzed upon 980 nm laser excitation. A strategy to enhance the optical temperature sensing performance is demonstrated via flexibly selecting diverse non-thermally coupled energy levels of dual luminescence centers with the fluorescence intensity ratio technology. The maximum values of absolute and relative sensitivity for the thermometer reach 0.2478 K−1 and 1.38% K−1 based on the non-thermally coupled energy levels of 3F2,3 (Tm3+)/5S2,5F4 (Ho3+). The luminescence color of La2Mo2O9:Yb3+, Ho3+, Tm3+ phosphors can maintain in the white region over the whole measured temperature range. These results indicate that the phosphors possess great potential in broad application prospects in the aspects of anti-counterfeiting, displays and non-contact temperature sensing.

Towards highly efficient NIR II response up-conversion phosphor enabled by long lifetimes of Er3+

The second near-infrared (NIR II) response photon up-conversion (UC) materials show great application prospects in the fields of biology and optical communication. However, it is still an enormous challenge to obtain efficient NIR II response materials. Herein, we develop a series of Er3+ doped ternary sulfides phosphors with highly efficient UC emissions under 1532 nm irradiation. β-NaYS2:Er3+ achieves a visible UC efficiency as high as 2.6%, along with high brightness, spectral stability of lights illumination and temperature. Such efficient UC is dominated by excited state absorption, accompanied by the advantage of long lifetimes (4I9/2, 9.24 ms; 4I13/2, 30.27 ms) of excited state levels of Er3+, instead of the well-recognized energy transfer UC between sensitizer and activator. NaYS2:Er3+ phosphors are further developed for high-performance underwater communication and narrowband NIR photodetectors. Our findings suggest a novel approach for developing NIR II response UC materials, and simulate new applications, eg., simultaneous NIR and visible optical communication.

(Keynote) Rational Design of Quantum Dot/Mediator Interfaces for Triplet Energy Transfer and Photon Upconversion

Photon upconversion, where two or more low energy photons are converted into one high energy photon, shows great potential in bioimaging, catalysis and solar energy conversion. Photon upconversion has traditionally been realized with lanthanide-doped nanoparticles, or organic dye sensitized triplet-triplet annihilation (TTA) based upconversion platforms. In recent years, QD sensitized triplet-triplet annihilation based upconversion systems have achieved impressive upconversion quantum efficiency and demonstrated many unique advantages, including high photostability, large extinction coefficient, high spectral coverage and tunability, and low singlet-triplet energy gap. In this talk, we discuss our recent work in developing and understanding QD/mediator interface for efficient QD-sensitized photon upconversion. We summarize the main results of time-resolved spectroscopic studies of various factors affecting the rate of triplet energy transfer (TET) from the QD to the surface attached mediator (TET1) and from the mediator to the emitter in solution (TET2). To identify the key design rules, we compare three PbS sensitized upconversion systems using three mediator molecules with the same tetracene triplet acceptor at different distances from the QD. Our results show that the mediator triplet state is mostly formed by direct TET from quantum dot. With increasing distance between the mediator and PbS QD, the efficiency of the TET1 from the QD to the mediator decreases due to a decrease in the rate of this triplet energy transfer step, while the efficiency of the TET2 from the mediator to emitter increases due to a reduction in the QD induced mediator triplet state decay (via the external heavy atom effect). The rate constant of TET2 is three orders of magnitude slower than the diffusion limited value. We show that the effect of QD/mediator on the total unconversion efficiency measured under CW illumination conditions can be well accounted for by the independently determined efficiencies of TET1 and TET2 steps, providing important insight on the design and rational improvement of efficient photon upconversion systems. Ongoing detailed mechanistic studies of the TET1 process shows that both QD bright and dark exciton states contribute to the TET process and higher lying bridge states play significant role in enhancing TET from core/shell QDs.

Red-diode-clad-pumped Er3+/Dy3+ codoped ZrF4 fiber: A promising mid-infrared laser platform.

We report, for the first time, to the best of our knowledge, mid-infrared (mid-IR) laser generation, from a red-diode-clad-pumped Er3+/Dy3+ codoped ZrF4 fiber laser. A free-running laser at ∼3.4 µm, mainly from the 4F9/2→4I9/2 transition of Er3+, directly excited by a 659-nm laser diodehas been achieved at room temperature with a maximum power of 0.8 W and 8.8% slope efficiency. In this system, the long-lived 4I11/2 and 4I13/2 states are rapidly depopulated by energy transfer to the codoped Dy3+ ions and energy transfer upconversion between the Er3+ ions, resulting in the accelerated recycling of ions. Additionally, the free-running dual-wavelength operation state at ∼3.3 and ∼3.5 µm is also observed, producing a total maximum power of 0.95 W with 10.7% slope efficiency, representing the first watt-class output from a diode-pumped rare-earth-doped fiber laser far beyond 3 µm. By employing a diffraction grating, continuous spectral tuning across the 642-nm range from 3053.9 to 3695.9 nm has been demonstrated. The proposed scheme provides, to the best of our knowledge, a promising new platform for laser generation in the mid-IR region of 3-4 µm.

Synthesis and characterization of red-emitting Yb/Ho-CaSiO3 upconversion phosphors

Host material plays an important role in obtaining efficient photon upconversion and downshifting luminescence. Generally, fluoride and oxyfluoride glasses-based materials are used for high-efficiency photon upconversion. However, the poor thermal stability of fluoride glasses and the toxicity of fluorine ions limit their applications. In this report, Yb/Ho-doped CaSiO3 wollastonite phosphors have been demonstrated as efficient red-emitting upconversion phosphors. The phosphors have been synthesized by microwave hydrothermal process followed by heat treatment at 1050 ​°C in the air environment. 2M phase of the β-wollastonite has been confirmed by X-ray diffraction and Raman spectroscopy while the existence of the Yb and Ho dopants in the CaSiO3 lattice has been confirmed by X-ray photoelectron spectroscopy. The synthesized samples showed strong red upconversion emission centered at 662 ​nm and near-infrared downshifting emissions at 2016 ​nm upon 980 ​nm excitation. The emissions were found to depend significantly on the Ho concentration. Temporal evolution of the main emission bands was investigated to show that the energy transfer upconversion from Yb to Ho ions was responsible for the efficient upconversion and downshifting phenomenon.

Excited-state absorption in thulium-doped materials in the near-infrared.

Excited-state absorption (ESA) is a key process for upconversion pumping schemes of thulium (Tm3+) doped laser materials. We have systematically studied two ESA transitions in the near-infrared spectral range, namely 3F4 → 3F2,3 (at ∼1 µm) and 3F4 → 3H4 (at ∼1.5 µm), in various Tm3+-doped fluoride (ZBLAN glass, cubic KY3F10 and CaF2, tetragonal LiYF4 and LiLuF4, monoclinic BaY2F8 crystals) and oxide (cubic Y3Al5O12, orthorhombic YAlO3 crystals) laser materials, using a pump-probe method with a polarized light. An approach to calculate the constants of energy-transfer upconversion (ETU) is also presented.