Before the 1960s, all anti-Stokes emissions, which were known to exist, involved emission energies in excess of excitation energies by only a few kT. They were linked to thermal population of energy states above excitation states by such an energy amount. It was the well-known case of anti-Stokes emission for the so-called thermal bands or in the Raman effect for the well-known anti-Stokes sidebands. Thermoluminescence, where traps are emptied by excitation energies of the order of kT, also constituted a field of anti-Stokes emission of its own. Superexcitation, i.e., raising an already excited electron to an even higher level by excited-state absorption (ESA), was also known but with very weak emissions. These types of well-known anti-Stokes processes have been reviewed in classical textbooks on luminescence.1 All fluorescence light emitters usually follow the well-known principle of the Stokes law which simply states that excitation photons are at a higher energy than emitted ones or, in other words, that output photon energy is weaker than input photon energy. This, in a sense, is an indirect statement that efficiency cannot be larger than 1. This principle is

Upconversion and Anti-Stokes Processes with f and d Ions in Solids

This paper gives the 2010 self-consistent set of values of the basic constants and conversion factors of physics and chemistry recommended by the Committee on Data for Science and Technology (CODATA) for international use. The 2010 adjustment takes into account the data considered in the 2006 adjustment as well as the data that became available from 1 January 2007, after the closing date of that adjustment, until 31 December 2010, the closing date of the new adjustment. Further, it describes in detail the adjustment of the values of the constants, including the selection of the final set of input data based on the results of least-squares analyses. The 2010 set replaces the previously recommended 2006 CODATA set and may also be found on the World Wide Web at physics.nist.gov/constants.

/pdf/codata-recommended-values-of-the-fundamental-physical-4bsdant71c.pdf

CODATA Recommended Values of the Fundamental Physical Constants: 2006

We show theoretically with the simplest possible model that the intensity of an upconversion luminescence that is excited by the sequential absorption of n photons has a dependence on absorbed pump power P, which may range from the limit of Pn down to the limit of P1 for the upper state and less than P1 for the intermediate states. The two limits are identified as the cases of infinitely small and infinitely large upconversion rates, respectively. In the latter case, the dependence of luminescence intensities from intermediate excited states on pump power changes with the underlying upconversion and decay mechanisms. In certain situations, energy transfer upconversion and excited-state absorption can be distinguished by the measured slopes. The competition between linear decay and upconversion in the individual excitation steps of sequential upconversion can be analyzed. The influence of nonuniform distributions of absorbed pump power or of a subset of ions participating in energy-transfer upconversion is investigated. These results are of importance for the interpretation of excitation mechanisms of luminescent and laser materials. We verify our theoretical results by experimental examples of multiphoton-excited luminescence in Cs3Lu2Cl9:Er3+, Ba2YCl7:Er3+, LiYF4:Nd3+, and Cs2ZrCl6:Re4+.

Power dependence of upconversion luminescence in lanthanide and transition-metal-ion systems

The invention provides methods, compositions, and apparatus for performing sensitive detection of analytes, such as biological macromolecules and other analytes, by labeling a probe molecule with an up-converting label The up-converting label absorbs radiation from an illumination source and emits radiation at one or more higher frequencies, providing enhanced signal-to-noise ratio and the essential elimination of background sample autofluorescence The methods, compositions, and apparatus are suitable for the sensitive detection of multiple analytes and for various clinical and environmental sampling techniques

Up-converting reporters for biological and other assays using laser excitation techniques

For several decades there has been extensive research in the area of multiphoton spectroscopy. However, multiphoton processes have not found widespread applications due to the relatively low multiphoton absorption cross sections of most materials. A new generation of multifunctional organic materials with large multiphoton absorption cross sections has opened up a number of unique applications in photonics and biophotonics. Two-photon pumped upconversion lasing, multiphoton absorption-induced optical power limiting, multiphoton laser scanning microscopy, and two-photon three-dimensional optical data storage are some of the recent photonic applications of multiphoton processes highlighted in this article. Two-photon photodynamic therapy is another promising application to biophotonics which is also discussed here. .

https://iopscience.iop.org/article/10.1088/0034-4885/59/9/001/pdf

Nonlinear multiphoton processes in organic and polymeric materials

Continuous-wave laser operation in the violet at 380 nm has been achieved on the 4D3/2 → 4/11//2 transition in LaF3:Nd3+ at temperatures of <90 K. Two different upconversion pumping mechanisms resulted in laser action: (a) sequential two-step absorption of an IR (790-nm) photon and a yellow (590-nm) photon by the Nd3+ ions; (b) cooperative energy transfer upconversion following the absorption of one yellow (578-nm) photon per Nd3+ ion. At temperatures near 20 K up to 12-mW power at 380 nm was obtained using pump powers of several hundred milliwatts from two cw dye lasers and conservative 1 % output coupling. At 77 K, the output power decreased to ~4 mW.

Violet cw neodymium upconversion laser

Green laser emission at 551 nm was achieved in LiYF4:Er3+ by upconversion pumping with a near-infra-red diode laser at low temperature. Using a 2mm-long monolithic laser crystal the lasing threshold was reached with 34 mW of absorbed power from an AlGaAs diode-laser array.

551 nm diode-laser-pumped upconversion laser

The authors report the system penalty incurred by an optical-to-electronic wavelength selector that is based on sharing one of several wavelength channels by a single transimpedance amplifier through MESFET switches. It was found that for a system penalty of 1 dB, four metal-semiconductor-metal photodetectors can share a single transimpedance amplifier, whereas for a 2 dB penalty the number is eight.

Capacitive loading of optical/electronic wavelength selector for WDMA networks

Recently, there has been considerable progress in the development of rare-earth lasers pumped by upconversion excitation.1-4 In particular, laser operation at visible wavelengths shorter than those of the pump was demonstrated in YAlO3:Er3+ and YLiF4:Er3+ at 550 nm,1 and in LaF3:Nd3+ at 380 nm4 using either sequential two-photon absorption or energy transfer processes for upconversion pumping. Here we report two new laser transitions of the neodymium ion at 413.0 and 729.5 nm using upconversion pumping of YLiF4:Nd3+ at low temperatures.

Laser emission at 413 and 730 nm in upconversion-pumped YLiF 4 :Nd 3+

Atomic Hydrogen Hyperfine Structure Experiments

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