Energy Transfer Upconversion Research Articles

Infrared to visible up conversion energy transfer confined at ordered micro-ring structures

Infrared to visible up-conversion energy transfer processes are demonstrated in two dimensional ordered arrays of fluorescent Er3+:Yb3+:CaNb2O6 micro-rings embedded in LiNbO3 optical substrate. Spatially resolved confocal spectroscopy reveals that Yb3+→Er3+ energy transfer process only takes place at these confined ring spatial regions. Thus, the formation of rare earth based co-doped micro-rings can be used to generate green and red visible fluorescent ring emitters upon infrared diode laser excitation on wide spatial areas. The results allow to envisage diode pumped multi-color integrated photonic devices for high quality shadow-free phosphor displays.

Up-Conversion and Migration by Energy Transfer: A Mixed Model for Doped Luminescent Solids

From a fundamental and technological perspective energy transfer up-conversion in luminescent solids is a very important phenomenon that requires different viewpoints for understanding and modeling. The efficiency of this process increases in the presence of energy migration. In this work a model to study the energy migration effects on the up-conversion process for doped solid time-dependent luminescence is proposed. The model takes advantage of the Förster-like method to calculate the relevant quantity averages and a microscopic–macroscopic methodology to solve energy transfer mixed schemes. Along with adequately describing the experimental trends reported in the literature for the relevant involved states, the model separates the migration-excited transient population from the initially excited time-dependent population, which permits separate analysis of the dynamics of the components. This last aspect is difficult to achieve experimentally and, to our knowledge, has not been reported previously in the theoretical literature.

Efficient up-conversion emission and energy transfer in LaAlO3 doped with Er3+, Ho3+, and Yb3+ ions

The spectroscopic properties of LaAlO3 polycrystals doped with Er3+, Ho3+ and Yb3+ ions have been investigated. Very efficient up-conversion emission occurs upon IR excitation. The strongest luminescence has been observed for a sample doped with Er3+, Ho3+, and Yb3+ ions simultaneously and annealed at 1500°C. An efficient energy transfer to Yb3+ ions is observed when Er3+ or Ho3+ ions are excited. The energy transfer mechanisms are proposed.

被动调Q激光器优化的研究

Passively Q-switched laser is used widely for its simple and compact structure.The theory of recent years for passively Q-switched laser is summarized.Based on the theory,for the laser which has energy-transfer upconversion(ETU) can be designed in such way that the ETU loss being considered as the linear loss.For the two core parameters such as the reflectivity of the mirror and the transmission of the saturable absorber,direct relationship curves of the two important parameters are given.The method for improving the peak power is summarized according to the peculiar parameter α of passively Q-switched laser.When α is approaching infinity,the conclusion of passively Q-switched theory being approaching actively Q-switched theory is obtained and the two Q-switched theory is unified.

Efficient 1645 nm continuous-wave and Q‑switched Er:YAG laser pumped by 1532 nm narrow-band laser diode

Energy transfer upconversion induced thermal effects are mainly responsible for the low efficiency of laser diode pumped Er:YAG lasers. The current work adopts Er:YAG rods with 0.25% Er(3+) doping concentration, instead of the commonly used rods with 0.5% Er(3+) doping concentration. Results show that the thermal effect is greatly alleviated. A continuous-wave output of 10.2 W is obtained using 31 W incident pump power. Optical-optical efficiency is approximately 33%. Slope efficiency, with respect to the absorbed pump power, is as high as 83%, which is close to the quantum efficiency. In a Q-switched operation, 7 mJ pulses with a pulse width of ~65 ns are obtained at 100 Hz PRF.

Optical amplification in Er/Yb silicate strip loaded waveguide

An Er/Yb silicate strip loaded waveguide was fabricated for optical amplification purpose. A 2.4-μm-wide SiO2 strip was deposited on top of the Er/Yb silicate active layer. Experiment data showed a 5.5 dB signal enhancement in a 7.8-mm-long waveguide pumped by a laser of 372 mW at 1480 nm. The signal is not saturated and can be further enhanced by increasing pumping power and decreasing waveguide loss. The strong red light emission at 660 nm was also observed due to excited state absorption and Yb3+ participated energy transfer upconversion processes.

Energy level decay and excited state absorption processes in erbium-doped tellurite glass

The fundamental excited state decay processes relating to the 4I11/2 → 4I13/2 transition in singly Er3+-doped tellurite (TZNL) glass have been investigated in detail using time-resolved fluorescence spectroscopy. Selective laser excitation of the 4I11/2 energy level at 970 nm and selective laser excitation of the 4I13/2 energy level at 1485 nm has established that energy transfer upconversion by way of a dipole-dipole interaction between two excited erbium ions in the 4I13/2 level populates the 4I11/2 upper laser level of the 3 μm transition. This upconversion has been analyzed for Er2O3 concentrations between 0.5 mol. % and 2.2 mol. %. The 4I13/2 and 4I11/2 energy levels emit luminescence with peaks located at 1532 nm and 2734 nm, respectively, with radiative decay efficiencies of 65% and 6.8% for the higher (2.2 mol. %) concentration sample. The low 2.7 μm emission efficiency is due to the non-radiative decay bridging the 4I11/2 → 4I13/2 transition and energy transfer to the OH− groups in the glass. Excited state absorption was observed to occur from the 4I13/2 and 4I11/2 levels with peak absorptions occurring at 1550 nm and 971 nm, respectively. The decay time of the 4I11/2 excited state decreased with an increase in the Er3+ concentration, which related to energy transfer to OH− ions that had a measured concentration of 6.6 × 1018 cm−3. Results from numerical simulations showed that a population inversion is reached at a threshold pumping intensity of ∼80 kW cm−2 for a cw laser pump at 976 nm if [Er3+] ≥ 1.2 × 1021 cm−3 (or [Er2O3] ≥ 2.65 mol. %) without OH− impurities being present.

Tunable upconversion luminescence and energy transfer process between Yb3+ and Er3+ in the CaY4F14

Yb3+/Er3+ codoped CaY4F14 materials with tunable upconversion (UC) emission were prepared by a high temperature solid-state method. Based on the UC luminescence properties investigations, it was found that, under 980nm excitation, CaY4F14:Yb3+,Er3+ showed green–yellow–red upconversion luminescence by changing the composition of the Yb3+-Er3+ dopants. It was also found that the green and red emissions originated from the two photon processes, and the ground-state absorption (GSA), excited-state absorption (ESA) and energy transfer (ET) processes between Er3+/Yb3+ ions were involved in the upconverted emission mechanism. The measured lifetimes show a strong dependence on Yb concentration.

Er3+‐Doped Anatase TiO2 Nanocrystals: Crystal‐Field Levels, Excited‐State Dynamics, Upconversion, and Defect Luminescence

A comprehensive survey of electronic structure and optical properties of rare-earth ions embedded in semiconductor nanocrystals (NCs) is of vital importance for their potential applications in areas as diverse as luminescent bioprobes, lighting, and displays. Er3+ -doped anatase TiO2 NCs, synthesized via a facile sol-gel solvothermal method, exhibit intense and well-resolved intra-4f emissions of Er3+ . Crystal-field (CF) spectra of Er3+ in TiO2 NCs are systematically studied by means of high-resolution emission and excitation spectra at 10-300 K. The CF analysis of Er3+ assuming a site symmetry of C(2v) yields a small root-mean-square deviation of 25.1 cm(-1) and reveals the relatively large CF strength (549 cm(-1) ) of Er3+, thus verifying the rationality of the C(2v) symmetry assignment of Er3+ in anatase TiO2 NCs. Based on a simplified thermalization model for the temperature-dependent photoluminescence (PL) dynamics from (4) S(3/2) , the intrinsic radiative luminescence lifetimes of (4) S(3/2) and (2) H(11/2) are experimentally determined to be 3.70 and 1.73 μs, respectively. Green and red upconversion (UC) luminescence of Er3+ can be achieved upon laser excitation at 974.5 nm. The UC intensity of Er3+ in Yb/Er-codoped NCs is found to be about five times higher than that of Er-singly-doped counterparts as a result of efficient Yb3+ sensitization and energy transfer upconversion (ETU) evidenced by its distinct UC luminescence dynamics. Furthermore, the origin of defect luminescence is revealed based on the temperature-dependent PL spectra upon excitation above the TiO2 bandgap at 325 nm.

Optimizing the mode-to-pump ratio in end-pumped quasi-three-level Nd-doped lasers considering the energy-transfer upconversion

The reabsorption losses considering energy-transfer-upconversion effects and the losses due to energy-transfer upconversion are derived as a function of the mode-to-pump ratio and the output coupler transmission in end-pumped quasi-three-level Nd-doped lasers, respectively. The dependence of thermally induced diffraction losses on the mode-to-pump ratio and the output coupler transmission is investigated with the energy-transfer-upconversion effects considered. The mode-to-pump ratio with and without thermally induced diffraction losses considering the energy-transfer upconversion is optimized. The results show that the optimum mode-to-pump ratio with the upconversion effects is less than that in which the energy-transfer-upconversion effects are neglected.

Upconversion luminescence of an insulator involving a band to band multiphoton excitation process

A multiphoton process to the conduction band of the insulator Er2O3 is reported, which occurs in vacuum under near infrared excitation. The enormous upconversion intensity is two orders of magnitude greater than that in air, and also the intensity ratio for green and red emission bands is inverted. The mechanism is probed by experiments of laser power dependence, cathodoluminescence, photoconductivity dependence and chemical dilution, and it involves cross-relaxation energy transfer upconversion of erbium ions to reach the conduction band. The upconversion color is tunable by changes in pressure, laser diode intensity and wavelength, or dopant ion concentration.

Intense red upconversion fluorescence emission in NIR-excited erbium–ytterbium doped laponite-derived phosphor

In this report the optical properties and energy-transfer frequency upconversion luminescence of Er 3+/Yb 3+-codoped laponite-derived powders under 975 nm infrared excitation is investigated. The 75%(laponite):25%(PbF 2) samples doped with erbium and ytterbium ions, generated high intensity red emission around 660 nm and lower intensity green emission around 525, and 545 nm. The observed emission signals were examined as a function of the excitation power and annealing temperature. The results indicate that energy-transfer, and excited-state absorption are the major upconversion excitation mechanism for the erbium excited-state red emitting level. The precursor glass samples were also heat treated at annealing temperatures of 300 °C, 400 °C, 500 °C, and 600 °C, for a 2 h period. The dependence of the visible upconversion luminescence emission upon the annealing temperature indicated the existence of an optimum temperature which leads to the generation of the most intense and spectrally pure red emission signal.

Energy level decay processes in Ho3+-doped tellurite glass relevant to the 3 μm transition

The primary excited state decay processes relating to the 5I6 → 5I7 ∼ 2.9 μm laser transition in singly Ho3+-doped tellurite (TZBG) glass have been investigated in detail using time-resolved fluorescence spectroscopy. Selective laser excitation of the 5I6 energy level at 1151 nm and 5I7 energy level at 1958 nm has established that the rate of energy transfer up-conversion between holmium ions excited to the 5I7 level is negligible for Ho3+ concentrations up to 4 mol. %. Excited state absorption was not observed from either the 5I7 or 5I6 levels and the luminescence from the 5I7 and 5I6 energy levels was measured to peak at ∼2050 nm and ∼2930 nm, respectively. The 5I6 level has a low luminescence efficiency of ∼8.9% due to strong nonradiative multiphonon relaxation. In contrast, decay from the 5I7 level is essentially fully radiative. A linear decrease in the decay time of the 5I6 level with Ho3+ concentration augmentation results from energy transfer to OH− ions in the glass (with NOH ∼ 8.2 × 1017 ions cm−3) and reduces the luminescence efficiency of the 5I6 level to 8% for [Ho3+] = 4 mol. %. Numerical simulation of a fiber laser incorporating 4 mol. % Ho3+ showed that a population inversion of ∼7.8% is reached for square pulses of 100 μs duration and a repetition frequency of 20 Hz at a moderate pump intensity of 418 kW cm−2 if energy transfer to OH− radicals is neglected.

Spectroscopy and frequency upconversion of Er 3+ ions in fluorotellurite glasses

In this work we report the optical properties and upconversion luminescence of Er 3+ ions in TeO 2–WO 3–PbO–BaF 2 and TeO 2–TiO 2–Nb 2O 5–BaF 2 fluorotellurite glasses and their comparison with those of TeO 2–TiO 2–Nb 2O 5 glass. The optical properties of Er 3+ ions have been established in terms of absorption and emission spectra and lifetime measurements. The 1.5 μm emission cross-section has been determined from the line shape of the emission spectrum and the calculated emission probability for the 4I 13/2 level. The highest emission cross section (6.9 × 10 −21 cm 2) corresponds to the TeO 2–TiO 2–Nb 2O 5–BaF 2 glass with a figure of merit for the bandwidth of 524.4 cm 2 nm. Upconversion emissions at 530, 548 nm, and 660 nm have been obtained under infrared excitation at 800 nm in the 4I 9/2 level and compared with those obtained under one photon excitation. The green emission corresponding to the 4S 3/2 → 4I 15/2 transition is dominant in all glasses. The excitation wavelength dependence of the upconverted luminescence together with its time evolution after infrared pulsed excitation suggest that energy transfer upconversion processes are responsible for the green upconversion luminescence.

Near‐Infrared→Visible Light Upconversion in a Molecular Trinuclear d–f–d Complex

Giving the green light: The connection of two CrIII sensitizers around a central ErIII acceptor in a self-assembled cation provides high local metal concentrations that favor efficient nonlinear energy transfer upconversion luminescence (see picture). Upon selective low-energy near-infrared irradiation of CrIII-centered transitions, 1 displays an unprecedented molecular two-photon upconverted green ErIII-centered emission. Detailed facts of importance to specialist readers are published as ”Supporting Information”. Such documents are peer-reviewed, but not copy-edited or typeset. They are made available as submitted by the authors. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.

Visible and infrared luminescence properties of Er 3+-doped Y 2Ti 2O 7 nanocrystals

Er 3+-doped Y 2Ti 2O 7 nanocrystals were fabricated by the sol–gel method. While the annealing temperature exceeds 757 °C, amorphous pyrochlore phase Er x Y 2− x Ti 2O 7 transfers to well-crystallized nanocrystals, and the average crystal size increases from ∼70 to ∼180 nm under 800–1000 °C/1 h annealing. Er x Y 2− x Ti 2O 7 nanocrystals absorbing 980 nm photons can produce the upconversion (526, 547, and 660 nm; 2 H 11/2→ 4 I 15/2, 4 S 3/2→ 4 I 15/2, and 4 F 9/2→ 4 I 15/2, respectively) and Stokes (1528 nm; 4 I 13/2→ 4 I 15/2) photoluminescence (PL). The infrared PL decay curve is single-exponential for Er 3+ (5 mol%)-doped Y 2Ti 2O 7 nanocrystals but slightly nonexponential for Er 3+ (10 mol%)-doped Y 2Ti 2O 7 nanocrystals. For 5 and 10 mol% doping concentrations, the mechanism of up-converted green light is the two-photon excited-state absorption. Much stronger intensity of red light relative to green light was observed for the sample with 10 mol% dopant. This phenomenon can be attributed to the reduced distance between Er 3+–Er 3+ ions, resulting in the enhancement of the energy-transfer upconversion and cross-relaxation mechanisms.

Internal temperature measurement of an ytterbium doped material under laser operation

Temperature of the pumped volume of an ytterbium doped material has been measured while laser action is taking place. This is achieved by recording green emissions at 530 and 550 nm from Er3+ impurities. These emissions result from energy transfer upconversion processes between Yb3+ and Er3+. Experiments performed on a Yb3+:CaGdAlO4 crystal show the effect of pump power and laser wavelength on the sample internal temperature. Temperature variation along the sample length has also been measured. This method can complement data obtained by thermal cameras which can only access surface temperatures in most laser materials.

Photoluminescence of Er-doped silicon-rich oxide thin films with high Al concentrations

Er-doped silicon-rich oxide (SRO) thin films co-doped with Al in high concentrations were prepared by sputtering. Some films were deposited using a substrate heater (150 °C<Td<235 °C). Films deposited without using substrate heating were annealed to 700 °C. The photoluminescence (PL) of most of the former films was greater than the PL of the latter films. Excitation wavelength dependence (EWD) of Er ion emission presents variations as the O content decreases and the Al content increases. The dependence of the Er ion 980 nm peak PL with respect to the Er ion 1525 nm peak PL indicates that the first emission depends less on energy transfer upconversion (ETU) processes as the O content decreases and the Al content increases. Broadband excitable Er3+ infrared (IR) emission with less loss due to ETU processes is important for applications in photonics.

Energy transition between Y b3+ - Tm3+ - Gd3+ in Gd3+, Y b3+ and Tm3+ Co-doped fluoride nanocrystals

YF3: 20% Gd3+, 20% Y b3+, 0.5% Tm3+ nanocrystal has been synthesized by a hydrothermal method. The upconversion (UC) emission and energy transfer progresses between Gd3+- Y b3+- Tm3+ under a 980-nm continuous wave semiconductor laser diode excitation have been explored. The experimental results show that the violet and ultraviolet (UV) enhancement with Tm3+ upconversion emission occurs in the nanocrystal, and in the same time the UC emissions of Gd3+ from 6D9/2, 6IJ, 6P5/2, and 6P7/2 states to the ground state 8S7/2 are obtained, too. The dynamic analysis implies that, under 980-nm excitation, the nanocrystal dimension plays a key role in the efficient energy transfer processes between Gd3+- Y b3+- Tm3tt based on the energy matching conditions.

Ultraviolet emissions from Gd3+ ions excited by energy transfer from Ho3+ ions

Abstract Ultraviolet (UV) upconversion (UC) emissions of Gd 3+ ion were investigated in Y 1.838− x Gd x Yb 0.16 Ho 0.002 O 3 ( x =0, 0.16, 0.4, 1, 1.4) bulk ceramics under 976 nm laser diode (LD) excitation. The UC emissions centered at 309 and 315 nm are assigned to the transition of 6 P 5/2 → 8 S 7/2 (Gd) and 6 P 7/2 → 8 S 7/2 (Gd). The 6 P J levels of Gd 3+ ions are populated by an energy transfer (ET) process from 8 S 7/2 (Gd)+( 3 P 1 , 3 L 8 , 3 M 10 ) (Ho)→ 6 P J (Gd)+ 5 I 8 (Ho). A four-photon ET UC process was confirmed by the dependence of the 6 P 7/2 level emission intensity on the pumping power. We found that the intensity of the UC emissions increased with Gd 3+ ion concentration and peaked at 8 mol%, then starts to decrease until the Gd 3+ ion concentration reached 70 mol%. The variation in the UV emission intensity is the result of the competition between the ET process and concentration quenching effect. Theoretical calculations based on steady-state equations validated the proposed UC mechanisms.