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

Recent startling interest for lanthanide luminescence is stimulated by the continuously expanding need for luminescent materials meeting the stringent requirements of telecommunication, lighting, electroluminescent devices, (bio-)analytical sensors and bio-imaging set-ups. This critical review describes the latest developments in (i) the sensitization of near-infrared luminescence, (ii) “soft” luminescent materials (liquid crystals, ionic liquids, ionogels), (iii) electroluminescent materials for organic light emitting diodes, with emphasis on white light generation, and (iv) applications in luminescent bio-sensing and bio-imaging based on time-resolved detection and multiphoton excitation (500 references).

/pdf/lanthanide-luminescence-for-functional-materials-and-bio-1w9cppwf8r.pdf

Lanthanide luminescence for functional materials and bio-sciences

Intracavity semiconductor saturable absorber mirrors (SESAM's) offer unique and exciting possibilities for passively pulsed solid-state laser systems, extending from Q-switched pulses in the nanosecond and picosecond regime to mode-locked pulses from 10's of picoseconds to sub-10 fs. This paper reviews the design requirements of SESAM's for stable pulse generation in both the mode-locked and Q-switched regime. The combination of device structure and material parameters for SESAM's provide sufficient design freedom to choose key parameters such as recovery time, saturation intensity, and saturation fluence, in a compact structure with low insertion loss. We have been able to demonstrate, for example, passive modelocking (with no Q-switching) using an intracavity saturable absorber in solid-state lasers with long upper state lifetimes (e.g., 1-/spl mu/m neodymium transitions), Kerr lens modelocking assisted with pulsewidths as short as 6.5 fs from a Ti:sapphire laser-the shortest pulses ever produced directly out of a laser without any external pulse compression, and passive Q-switching with pulses as short as 56 ps-the shortest pulses ever produced directly from a Q-switched solid-state laser. Diode-pumping of such lasers is leading to practical, real-world ultrafast sources, and we will review results on diode-pumped Cr:LiSAF, Nd:glass, Yb:YAG, Nd:YAG, Nd:YLF, Nd:LSB, and Nd:YVO/sub 4/.

/pdf/semiconductor-saturable-absorber-mirrors-sesam-s-for-5fvewzfxqk.pdf

Semiconductor saturable absorber mirrors (SESAM's) for femtosecond to nanosecond pulse generation in solid-state lasers

Visible-light persistent phosphors are being widely used as self-sustained night-vision materials because of their sufficiently strong and long afterglow (>10 h) and their ability to be excited by sunlight as well as room light. In contrast, persistent phosphors for near-infrared (NIR) wavelengths are lacking. Here we report a series of Cr(3+)-doped zinc gallogermanate NIR persistent phosphors that exhibit strong emission at 650-1,000 nm, extending beyond the typical 690-750 nm, and with a super-long afterglow of more than 360 h. These new NIR persistent phosphors are all-weather materials that can be rapidly, effectively and repeatedly charged by natural sunlight in almost all kinds of outdoor environment. Seconds to minutes of sunlight activation can result in more than two weeks of persistent NIR light emission. This new series of NIR persistent materials have potential applications in night-vision surveillance, solar energy utilization and in vivo bio-imaging.

Sunlight-activated long-persistent luminescence in the near-infrared from Cr 3+ -doped zinc gallogermanates

Nonlinear Optical Crystals: A Complete Survey

We have carried out a detailed spectroscopic characterization of Nd: GdVO4, a new laser crystal with high effective absorption and emission cross sections. The accidental degeneracy of the upper4
F
3/2 laser level decreases the number of emission lines and creates -together with the anisotropic crystal field - high emission cross sections (7.6 × 10−19 cm2 at 1.06 µm and 300 K). In addition, the lines are strongly homogeneously broadened (1.6 nm for the 808.4 nm diode-laser pump transition). The temperature dependences of lifetime, linewidths, and cross sections have been determined. Slope efficiencies up to 57% with respect to the absorbed diode-laser pump power and output powers up to 0.8 W have been achieved at 1.06 µm from a 2 mm long crystal. Intracavity second-harmonic generation, using a KTP crystal, is demonstrated.

Spectroscopic characterization and laser performance of diode-laser-pumped Nd: GdVO4

Spectroscopic properties and laser performance of Yb-doped tungstates at pulsed Ti:sapphire laser pumping are reported. Room-temperature lasing near 1025  nm is demonstrated in Yb:KY(WO4)2 and Yb:KGd(WO4)2, with a slope efficiency as great as 86.9%.

Pulsed laser operation of Yb-doped KY(WO 4 ) 2 and KGd(WO 4 ) 2

We have investigated the basic spectroscopic properties of Cr3+-doped gallium garnets. Weak crystal fields (Dq/B=2.39–2.55) lead to broad4
T
2→4
A
2 fluorescence in the 700–950 nm range depending on the chemical composition of the crystals. At room temperature the4
T
2→4
A
2 transition is homogeneously broadened, whereas the 4 K spectra of the2
E→4
A
2 transition show inequivalent Cr3+ sites and inhomogeneous linewidths of 8 cm−1 in these laser crystals. From 300 to 4 K, the oscillator strength of the4
T
2→4
A
2 transition is reduced by a factor of about 0.6 due to the temperature dependent electron phonon coupling. The transition probability of the2
E→4
A
2 transition correlates with the energetic position of the4
T
2 level, which is admixed into the2
E level via spin-orbit coupling. The comparison of the2
E→4
A
2 phonon sideband structure in garnets of different chemical compositions allows the assignment of some peaks to GaO4-tetrahedron modes of the garnet structure.

The effect of the crystal field strength on the optical spectra of Cr3+ in gallium garnet laser crystals

Single crystals of gadolinium vanadate doped with neodymium ions have been grown by the Czochralski method. The absorption and luminescence spectra of the neodymium have been measured. The absorption near 0.8 μm is higher than 70 cm−1. The lifetime of the neodymium ions is 90 μs. Laser action has been achieved on the transitions 4F3/2 → 4I13/2, 4I11/2. The differential efficiency of the lasing near 1.06 μm is 54%.

https://iopscience.iop.org/article/10.1070/QE1992v022n12ABEH003672/pdf

The Nd:GdVO4 crystal: a new material for diode-pumped lasers

Room temperature cw laser action of Yb3+-doped KY(WO4)2 and KGd(WO4)2 crystals at 1.025 μm and Er, Yb : KY(WO4)2 at 1.54 μm has been demonstrated under pumping by both Ti-sapphire laser and InGaAs laser diodes. A slope efficiency of Yb-lasers up to 78% has been obtained.

G. Huber

Papers

Spectroscopic characterization and laser performance of diode-laser-pumped Nd: GdVO4

Pulsed laser operation of Yb-doped KY(WO 4 ) 2 and KGd(WO 4 ) 2

The effect of the crystal field strength on the optical spectra of Cr3+ in gallium garnet laser crystals

The Nd:GdVO4 crystal: a new material for diode-pumped lasers

CW laser performance of Yb and Er,Yb doped tungstates