Upconversion Devices Research Articles

Investigation of up-conversion luminescence of Er3+ and Er3+/Yb3+ ions doped in PLZT for active electro-optical applications

The up-conversion luminescence of Er3+ and Er3+/Yb3+ ions doped in lanthanum-modified lead zirconate titanate (PLZT) under 980 nm excitation at room temperature has been investigated. The green up-conversion luminescence at 540 and 566 nm was observed in Er3+:PLZT; the greater the concentration of Er3+ ions, the stronger the intensity. In Er3+-Yb3+:PLZT, other than the green up-conversion luminescence at 540 and 566 nm, a relatively weak red up-conversion luminescence at 668 nm was also observed. Both green and red up-conversion luminescence intensities presented an approximately quadratic dependence on excitation power, which indicated that two excitation photons are involved in the up-conversion process of Er3+:PLZT and Er3+-Yb3+:PLZT. The characteristics of PLZT ceramic material were also studied by Raman spectroscopy. This work shows a promising future for developing multifunctional up-conversion electro-optical devices using Er3+ and Er3+/Yb3+ ions doped PLZT.

Optical upconversion devices based on photosensitizer-doped organic light-emitting diodes

The optical upconversion of infrared light to visible light has been achieved in photosensitizer-doped organic light-emitting diodes, where poly(N-vinylcarbazole) doped with infrared photosensitizer of 2,4,7-trinitro-9-fluorenylidene)malonitrile was used as hole-transporting layer, and tris(8-hydroxyquinoline) aluminum acted as both emitting and electron-transporting layers. Both electroluminescent intensity and current were enhanced under infrared illumination. The enhancement ratio was obtained as 2.45 times for electroluminescent emission and 1.45 times for current. This work brought forth a prototype design for novel flexible organic optical upconversion device used in near infrared field.

Optical switch and luminescence properties of sol–gel hybrid organic–inorganic materials containing azobenzene groups and doped with neodymium ions

TiO2/γ-glycidoxypropyltrimethoxysilane and methyltrimethoxysilane hybrid organic–inorganic material, which contains azobenzene groups and is doped with neodymium ions, was prepared by a low temperature sol–gel technique. The trans-cis-trans photoisomerization cycles of the hybrid film were investigated by a photoirradiation with UV light followed by visible light. An intense room-temperature upconversion emission at 397 nm was also measured from a hybrid film heated at a low temperature of 80 °C upon excitation with a xenon lamp at a wavelength of 580 nm. The mechanism of the upconversion is proposed and indicates that the sequential two-photon absorption process originating from the long-lived 4F3/2 excited state should be responsible for the up-conversion process. These results indicate that the prepared hybrid materials with multifunctional photonic properties are promising candidates for integrated optics and photonic applications, which would allow directly integrating onto a single chip, the upconversion device with the pump source, and optical data storage and optical switching devices.

Powerful visible upconversion fluorescence of Er3+ in novel bismuth gallate glasses compared with in common tellurite glasses

Powerful visible upconversion fluorescence intensities of Er3+ in novel bismuth gallate glasses (LKBBG) and common tellurite glasses (TZN) with low phonon energies and high refractive indices have been compared. Under the same measurement condition, Er3+-doped LKBBG glasses show the stronger upconversion emission intensities than Er3+-doped common tellurite glasses (TZN). The visible upconversion emission bands peaked at 531, 548 and 668nm have been confirmed that two photons contribute to these upconversion processes. The maximum phonon energy obtained in LKBBG glasses is 673cm−1, which is 65cm−1 lower than that in common tellurite glasses, indicating that LKBBG glasses almost possess the lowest maximum phonon energy in all of the oxide glasses. All analyses support that Er3+-doped LKBBG glasses are promising materials for fabricating visible upconversion devices.

Midinfrared optical upconverter

We have developed a midinfrared optical upconverter by wafer bonding a GaAs∕AlGaAs light-emitting diode with an InSb p+nn+ photodetector. The device converts midinfrared radiation in the range of 3–5.45μm to near-infrared light at 0.84μm, which can be efficiently detected using a widely available Si charge coupled device. At 77K, the measured external upconversion efficiency was 0.093W∕W. The optical up-conversion device, in combination with the Si CCD camera, leads to an alternative solution for making low-cost and large-area midinfrared imaging device. Effects of electrical gain and photon recycling inside this integrated device are discussed.

Thermal stability, Judd–Ofelt theory analysis and spectroscopic properties of a new Er 3+/Yb 3+-codoped germano-tellurite glass

The Er 3+/Yb 3+-codoped 70TeO 2–5Li 2O–10B 2O 3–15GeO 2 glass was prepared. The thermal stability, absorption spectra, emission spectra and up-conversion spectra were measured and investigated. The Judd–Ofelt analysis based on absorption spectra was performed in order to determine the Judd–Ofelt intensity parameters Ω t ( t = 2, 4, 6), spontaneous emission probability, radiative lifetime and branching ratios of several Er 3+ transitions. It was found that this studied glass has good thermal stability, broad fluorescence full width at half maximum (FWHM), large stimulated emission cross-section and strong up-conversion emissions at about 532, 546 and 659 nm, corresponding to the 2H 11/2 → 4I 15/2, 4S 3/2 → 4I 15/2 and 4F 9/2 → 4I 15/2 transitions of Er 3+, respectively under the excitation at 970 nm. The results suggest that this Er 3+/Yb 3+-codoped germano-tellurite glass may be a potentially useful material for developing potential amplifiers and up-conversion optical devices.

Optimized GaAs∕AlGaAs light-emitting diodes and high efficiency wafer-fused optical up-conversion devices

Achieving a high internal quantum efficiency in GaAs∕AlGaAs based light-emitting diodes (LEDs) for room-temperature operation at low current-density injection is crucial for applications such as optical up-converters based on the integration of LEDs and photodetectros. We report the experimental results as well as the theoretical analyses of the internal quantum efficiency of GaAs∕AlGaAs LEDs as a function of the p-doping concentration of the active region for low current injection operation. By optimizing the doping concentration, we have achieved a close to 100% internal quantum efficiency for room-temperature operation of LEDs in the low injection current-density range, i.e., around 0.1A∕cm2. An optical up-converter was fabricated using wafer-fusion technology by integrating the optimized GaAs∕AlGaAs LED with an InGaAs∕InP photodetector. The internal up-conversion quantum efficiency was measured to be 76%.

Effects of chloride introduction on up-conversion luminescence in Tm 3+-doped tellurite glasses

Blue up-conversion luminescence properties in Tm 3+-doped lead chloride tellurite glasses have been studied under 980 nm excitation. The intense blue and relatively weak red emissions centered at 476 and 649 nm corresponding to the transitions 1 G 4→ 3 H 6 and 1 G 4→ 3 H 4 of Tm 3+, respectively, are simultaneously observed at room temperature. The effect of PbCl 2 on up-conversion intensity is observed and discussed, and possible up-conversion mechanisms are evaluated. The intense blue up-conversion luminescence of Tm 3+-doped lead chloride tellurite glasses may be a potentially useful material for developing up-conversion optical devices.

1.5 μm to 0.87 μm optical upconversion using wafer fusion technology

Wafer fusion is an important processing tool for heterogenous integration of different materials regardless of their lattice constants. It removes the limitation of conventional epitaxial growth techniques and introduces a design parameter for achieving high performance semiconductor devices. In this article, we propose and demonstrate a 1.5 μm to 0.87 μm optical upconversion device based on wafer fusion technology. The device consists of an In0.53Ga0.47As (InGaAs) p-i-n photodetector and an AlGaAs/GaAs light-emitting diode (LED) integrated with wafer fusion. Incoming 1.5 μm light is absorbed by the InGaAs photodetector and generates a photocurrent. The resultant photocurrent drives the GaAs LED, which emits radiation at 0.87 μm. An internal quantum efficiency of 20% and an external quantum efficiency of 0.27% was obtained at room temperature. The results show the potential of the upconversion device in near-infrared imaging applications.

Negative luminescence in semiconductors: a retrospective view

Twenty-five years ago, we introduced the phenomenon of negative luminescence (NL) into semiconductor physics. This paper provides an overview of work conducted to develop this fundamental concept. Initially, we consider the first-principle approach to radiation interaction with basic matter and the major properties of NL. Then we describe the problems of NL direct measurements in homogeneous materials and structures. Finally, we emphasize the use of NL approach in applications involving devices for infrared (IR) wavelength (3– 12 μm ) high-temperature (300– 400 K ) optoelectronics. Our subjects will include NL IR emitting diodes, radiative coolers, IR dynamic scene simulators, light up-conversion devices, and the Stealth effect in IR.

1.5 to 0.87 [micro sign]m optical upconversion device fabricated by wafer fusion

A 1.5 to 0.87 µm wavelength optical upconversion device fabricated by wafer fusion is proposed and demonstrated. The device consists of an In0.53Ga0.47As/InP pin photodetector and a GaAs/AlGaAs light emitting diode, which were grown separately and wafer bonded together. The internal upconversion quantum efficiency is measured to be 18% at room temperature.

1.5 [micro sign]m up-conversion device

An epitaxially integrated 1.5 to 1 µm up-conversion device is reported. The device consists of a serially connected In0.53Ga0.47As photodiode and InAs0.1P0.9 light emitting diode, grown on InP. The device operation relies first on detecting a 1.5 µm signal by the photodiode and secondly on driving the emitter by the resulting photocurrent, thus achieving the up-conversion.

Pixelless infrared imaging utilizing a p-type quantum well infrared photodetector integrated with a light emitting diode

We present experimental results which support a recently proposed scheme for infrared imaging through the combined use of a photon frequency up-conversion device with a charge coupled device (CCD) camera. The epitaxial device consists of a long wavelength p-type GaAs/AlGaAs quantum well infrared photodetector (QWIP) on top of which is grown a shorter wavelength InGaAs/GaAs light emitting diode (LED). Upon long wavelength infrared excitation of the QWIP, near infrared light is generated by the LED whose output is directed towards a commercial CCD array where the up-converted image of the long wavelength infrared source object is formed.

Luminescence processes in Tm3+- and Er3+-ion-activated, Yb3+-ion-sensitized infrared upconversion devices

Frequency upconversion characteristics in Er3+- or Tm3+-ion-activated and Yb3+-ion- sensitized luminescent materials have been investigated. The principal goal was to obtain high-brightness, blue and green light sources under 980 nm emitting laser diode light excitation. Processes leading to the efficient upconversion have been investigated both by experimental and analytical methods. It has been shown that upconversion efficiencies are principally determined with Yb3+ ion excited state lifetime, which is highly influenced by device optical confinement as well as material characteristics. The effect of the optical confinement has been analyzed quantitatively on the basis of a rate equation model. Criteria for realizing efficient infrared upconversion devices have been presented. A strong tendency toward temperature quenching has been observed especially in blue emitting materials. This temperature dependence has been shown to be principally due to increase of nonradiative decay in the Yb3+ ion excited state.

Upconversion fluorescences of TeO 2- and Ga 2O 3-based oxide glasses containing Er 3+

Upconversion-pumped fluorescence was observed for the first time in Er 2O 3-doped oxide glasses even at room temperature without any sensitizing ions such as Yb 3+ in the systems of TeO 2- and Ga 2O 3-based oxide glasses. A diode laser operating at 798 nm was used as the pumping source for stepwise excitation. The upconversion-pumped fluorescence was confirmed by the quadratic changes of fluorescence intensity against the pumping power. It is suggested that these oxide glasses can become one candidate for a high temperature upconversion device.

Energy transfer between Er3+ and Tm3+ ions in a barium fluoride-thorium fluoride glass.

The up-conversion of infrared radiation into green, red, and 805-nm fluorescence has been studied for ${\mathrm{Er}}^{3+}$ and ${\mathrm{Tm}}^{3+}$ ions in both ${\mathrm{Yb}}^{3+}$-doped and non-${\mathrm{Yb}}^{3+}$-doped ${\mathrm{BaF}}_{2}$-${\mathrm{ThF}}_{4}$ fluoride glass over a wide temperature range and several dopant concentrations. It has been found that the addition of ${\mathrm{Tm}}^{3+}$ preferentially quenches the up-conversion efficiency of the green emission corresponding to a transition from the $^{4}\mathrm{S}_{3/2}$ level of ${\mathrm{Er}}^{3+}$. The decrease in emission amounts to a factor of about 50 for a concentration of 0.5 mol % ${\mathrm{TmF}}_{3}$ at 300 K. The quenching effect is discussed in terms of energy transfer between ${\mathrm{Er}}^{3+}$ and ${\mathrm{Tm}}^{3+}$ ions. A rate equation model and a Judd-Ofelt analysis used in conjunction with the appropriate optical data lead to an understanding of the up-conversion process. The absolute values of the energy transfer rates and the electron populations in the lower excited states of the excited ${\mathrm{Er}}^{3+}$ and ${\mathrm{Tm}}^{3+}$ ions can be determined. This information should enable researchers to tailor materials to improve the efficiency of the up-conversion and laser devices.