Orange Spectral Region Research Articles

Spectroscopic properties of Sm3+-doped oxy-fluoride powders with various Sm3+ concentration and sintering temperature

Sm3+-doped oxy-fluoride (OFSm) powders are prepared by the melt quenching technique and characterized using FE-SEM, optical absorption and emission techniques. Spectroscopic properties of Sm3+-doped oxy-fluoride powders with different Sm3+ concentration and sintering temperature are presented and discussed by using the absorption, emission measurements. The Judd–Ofelt intensity (J–O) parameters (Ωλ, where λ=2, 4 and 6), measured from the experimental oscillator strengths of the absorption spectra, are used to evaluate the radiative parameters of the fluorescence transitions. Intense orange emission can be obtained when excited with 325nm wavelength by increasing the sintering temperature to 1400°C. Ratio of fluorescence intensities arising from the two closing lying 4F3/2 and 4G5/2 levels is studied, concentration quenching has been noticed beyond 2mol% of Sm3+ ions concentration. The excellent spectroscopic properties along with the outstanding thermal stability suggest that the OFSm03 powders may become an attractive laser material to exhibit efficient visible lasing emission in the orange spectral region.

Crystalline Waveguide Lasers in the Visible and Near-Infrared Spectral Range

This paper summarizes our recent results on crystalline waveguides and waveguide lasers fabricated by the femtosecond-laser writing technique. Highly efficient waveguide lasers emitting in the near infrared spectral range based on ytterbium and neodymium doped Y <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Al <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">5</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">12</sub> with slope efficiencies above 70% and continuous wave output powers of more than 5 W were demonstrated. Furthermore, pulsed laser operation of passively Q-switched Yb:YAG and Nd:YAG wavequide lasers was achieved by incorporating the saturable absorber Cr <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4+</sup> :YAG in a monolithic setup. Based on fs-laser written curved structures in Yb:YAG, efficient curved waveguide lasers could be demonstrated. Also, waveguide lasers in the visible spectral range were investigated. We achieved laser emission in the green, orange, red and deep-red spectral region and could demonstrate output powers of more than 1 W with waveguides based on praseodymium doped materials. Additionally, switchable and dual wavelength operation between the orange and red laser emission was achieved. By utilizing the nonlinear crystal KTiOPO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> as substrate material for fs-laser inscription, nonlinear waveguides were realized. With these devices, efficient second harmonic generation into the blue and green spectral range was achieved.

Optical properties and electronic band structure of BiMg2PO6, BiMg2VO6, BiMg2VO6:Pr3+ and BiMg2VO6:Eu3+

The luminescence properties of the yellow pigment BiMg2VO6 are revisited and those of BiMg2PO6, BiMg2VO6:Pr3+ and BiMg2VO6:Eu3+ are described. It is shown that the undoped systems exhibit broad band emission in the green or orange spectral regions, but only upon UV or near UV excitation. In contradiction with a previous report, we found that the blue, host absorbed, photons are lost non-radiatively and do not contribute to the luminescence processes in BiMg2VO6. To understand these experimental results, the optical properties of BiMg2VO6 and BiMg2PO6 are theoretically analysed on the basis of electronic structure diagrams calculated by the DFT method. It is found that the optical transitions are mostly localised within [VO4]3− units or non-regular Bi3+ ions and occur in the UV or near UV regions. The luminescence of the trivalent lanthanide dopants is weak (Eu3+) or unobserved (Pr3+) in BiMg2VO6 which is explained by inefficient energy migration in the host lattice to the impurity sites.

A single-phase, color-tunable, broadband-excited white light-emitting phosphor Y2WO6: Sm3+

Un-doped and Sm3+ doped Y2WO6 were synthesized with solid state reactions. X-ray diffraction measurements show that all the samples present single-phase Y2WO6. The combination of blue emission in a broad band from the host and several groups of emission lines in yellow, orange, and red spectral region results in a desired white light. The chromaticity coordinates and color temperature can be tuned by changing the doping concentration of Sm3+. The mechanisms of energy transfer were analyzed. The present results prove Sm3+ doped Y2WO6 is a promising single-phase, color-tunable, broadband-excited white light-emitting phosphor based on AlGaN-based ultraviolet light-emitting diodes.

Structural and luminescence properties of Sm3+ ions in zinc fluorophosphate glasses

Sm3+-doped zinc fluorophosphate (PKAZLFSm) glasses have been prepared by conventional melt quenching technique and are characterized through thermal, Raman, absorption, emission and decay rate analysis. The Judd–Ofelt (JO) theory has been used to derive the spectroscopic properties of Sm3+:PKAZLFSm glasses. The decay rates for the 4G5/2 level of Sm3+ ions have been measured and are found to be single exponential at lower concentration (⩽0.1mol% Sm2O3) and turns into non-exponential at higher concentrations (⩾0.5mol% Sm2O3) due to energy transfer through cross-relaxation. The experimental lifetimes for 4G5/2 level of Sm3+ ions are found to decrease from 3.2 to 0.5ms when the concentration increased from 0.01 to 4.0mol% Sm2O3 due to energy transfer among Sm3+ ions. In order to know the nature of the energy transfer mechanism, the non-exponential decay rates are well fitted to Inokuti–Hirayama model for S=6, indicating that the energy transfer process is of dipole–dipole type. The results obtained for the 4G5/2→6H7/2 transition indicate that the Sm3+:PKAZLFSm10 glass can be very much useful for the development of visible lasers in the reddish orange spectral region.

Red and orange laser operation of Pr:KYF_4 pumped by a Nd:YAG/LBO laser at 4691nm and a InGaN laser diode at 444nm

We report the basic luminescence properties and the continuous-wave (CW) laser operation of a Pr(3+)-doped KYF(4) single crystal in the Red and Orange spectral regions by using a new pumping scheme. The pump source is an especially developed, compact, slightly tunable and intra-cavity frequency-doubled diode-pumped Nd:YAG laser delivering a CW output power up to about 1.4 W around 469.1 nm. At this pump wavelength, red and orange laser emissions are obtained at about 642.3 and 605.5 nm, with maximum output powers of 11.3 and 1 mW and associated slope efficiencies of 9.3% and 3.4%, with respect to absorbed pump powers, respectively. For comparison, the Pr:KYF(4) crystal is also pumped by a InGaN blue laser diode operating around 444 nm. In this case, the same red and orange lasers are obtained, but with maximum output powers of 7.8 and 2 mW and the associated slope efficiencies of 7 and 5.8%, respectively. Wavelength tuning for the two lasers is demonstrated by slightly tilting the crystal. Orange laser operation and laser wavelength tuning are reported for the first time.

Red and orange Pr^3+:LiYF_4 planar waveguide laser

In this Letter we report on room temperature continuous wave laser operation in the red (639 nm, (3)P(0)→(3)F(2)) and orange (604 nm, (3)P(0)→(3)H(6)) spectral regions of Pr(3+)-doped LiYF(4) planar waveguides fabricated by liquid phase epitaxy. Output powers of 25 and 12 mW and slope efficiencies of 5% and 6% were achieved at 639 and 604 nm, respectively, by pumping with an optically pumped semiconductor laser operating at 479.2 nm.

Visible laser operation of Pr^3+-doped fluoride crystals pumped by a 469 nm blue laser

We report continuous-wave (CW) laser operation of Pr3+-doped LiLuY4, LiYF4 and KY3F10 single crystals in the Red, Orange and Green spectral regions by using a new pumping scheme. The pump source is an especially developed compact, slightly tunable and intracavity frequency-doubled diode-pumped Nd:YAG laser delivering a CW output power of 0.9W at 469.12 nm. At this pump wavelength, efficient room temperature laser emissions corresponding to the 3P0→3F2, 3P0→3H6 and 3P1→3H5 Pr3+ transitions are observed. While a maximum slope efficiency of 45% is obtained in the red with Pr:LiYF4, the demonstration is made for the first time of the orange laser operation of Pr:KY3F10 at about 610 nm.

Neutral copper(i) phosphorescent complexes from their ionic counterparts with 2-(2′-quinolyl)benzimidazole and phosphine mixed ligands

Neutral mononuclear Cu(I) complexes and their counterparts with counterion, i.e. Cu(qbm)(PPh(3))(2), Cu(qbm)(DPEphos), [Cu(Hqbm)(PPh(3))(2)](BF(4)) and [Cu(Hqbm)(DPEphos)](BF(4)), where Hqbm = 2-(2'-quinolyl)benzimidazole, DPEphos = bis[2-(diphenylphosphino)phenyl]ether, have been synthesized and characterized by X-ray structure analyses. All of the four complexes in solid state exhibit a strong phosphorescence band in the orange spectral region at room temperature. The photophysical properties of these complexes in both methylene chloride solution and poly(methyl methacrylate) film have been studied. Compared to the related cationic complexes, the neutral ones show blue-shifted emissions and longer lifetimes that can be attributed to the additional ligand-centered π-π* transition beside traditional metal-to-ligand charge-transfer (MLCT). By doping these complexes in N-(4-(carbazol-9-yl)phenyl)-3,6-bis(carbazol-9-yl) carbazole (TCCz), multilayer organic light-emitting diodes (OLEDs) were fabricated with the device structure of ITO/PEDOT/TCCz: Cu(I) (10 wt%)/BCP/Alq(3)/LiF/Al. The neutral complex Cu(qbm)(DPEphos) exhibits a higher current efficiency, up to 8.87 cd A(-1), than that (5.58 cd A(-1)) of its counterpart [Cu(Hqbm)(DPEphos)](BF(4)).

Lanthanide-Containing 2,2′-Bipyridine Bridged Urea Cross-Linked Polysilsesquioxanes

ABSTRACT Urea-based bis-silylated 2,2′–Bipyridine (bpy) organic–inorganic hybrids incorporating different lanthanide (Ln3+) ions (Eu3+, Gd3+, Tb3+ or Eu3+/Tb3+) were obtained by the sol–gel process. The structure and the emission characteristics of the hybrids were ascertained using X-ray diffraction, nuclear magnetic resonance, Fourier transform infrared spectroscopy, photoluminescence, and quantum yield measurements. The hybrids feature both the emission of the host and the Eu3+ and/or Tb3+ transitions allowing a fine-tuning of the color from the blue to the red, orange, or green spectral regions. Bpy-to-Ln3+ and Tb3+-to-Eu3+ energy transfer mechanisms are demonstrated and the hybrids present slightly distinct Ln3+ coordination spheres due to the different bpy/Ln3+ ratios.

Red to orange electroluminescence from InP/AlGaInP quantum dots at room temperature

We demonstrate the growth of electrically driven InP/AlGaInP quantum dots embedded in a p–i–n diode structure emitting in the red to orange spectral region at room temperature. We observed an increase in emission wavelength by decreasing the quantum dot growth temperature from 710 down to 670 °C. Due to the decreased diffusion length the incorporation of Al from the AlGaInP barrier into the InP quantum dots is reduced and results in a strong red shift of the electroluminescence of up to 95 nm (620–715 nm). Electrically driven photon correlation measurements (5 K) performed on a single quantum dot under continuous current show a clear antibunching behavior ( g ( 2 ) ( 0 ) = 0.41 ) as expected for a single-photon emitter.

Optimizing non-resonant frequency conversion in periodically poled media

Non-resonant frequency conversion into the blue, green, orange, and red spectral regions is reported. Fundamental light sources were continuous-wave non-planar monolithic single-mode ring Nd : YAG lasers as well as a standing-wave multi-mode Nd : YAG laser. Periodically poled KTiOPO4 was employed as the nonlinear medium, but the considerations could also be applied to other periodically poled materials. A multi-pass scheme resulted in a normalized conversion efficiency as high as 27.2 % W-1 for frequency doubling in the small-signal regime at 1064 nm.

Light emission ranging from blue to red from a series of InGaN/GaN single quantum wells

In this paper, we describe the growth and characterization of InGaN single quantum wells with emission peaks in the blue, green, amber and red spectral regions, grown by metal-organic vapour phase epitaxy. Starting from the growth of a blue-emitting (peak ~430 nm) InGaN quantum well at 860°C the InGaN growth temperature was progressively reduced. The photoluminescence peak wavelength, measured at low temperature, shifts through the green and orange spectral regions and reaches 670 nm for an InGaN growth temperature of 760°C. This corresponds to an energy lower than the currently accepted band-gap of the binary compound, InN. Spectral characteristics of the luminescence peaks will be discussed, including an analysis of the phonon-assisted contribution. Low energy secondary ion mass spectrometry analysis provides information on the indium content and thickness of the `blue' and `red' quantum wells. The results are combined to discuss the origin of the `sub-band-gap' luminescence in terms of the combined influence of InN-GaN segregation and the effect of intense piezoelectric fields.

Use of CC traps with different trap base colors for silverleaf whiteflies (Homoptera: Aleyrodidae), thrips (Thysanoptera: Thripidae), and leafhoppers (Homoptera: Cicadellidae).

During 1996, 1997, and 1999, studies were conducted in cotton, sugar beets, alfalfa, yardlong bean, and peanut fields to compare insect catches in CC traps equipped with different trap base colors. The studies were conducted in southwestern United States, China, and India. The nine colors, white, rum, red, yellow, lime green, spring green, woodland green (dark green), true blue, and black, varied in spectral reflectance in the visible (400-700 nm) and near-infrared (700-1050 nm) portions of spectrum. Lime green, yellow, and spring green were the three most attractive trap base colors for silverleaf whitefly, Bemisia argentifolii Bellows & Perring, and leafhopper, Empoasca spp. adults. The three trap base colors were moderately high in the green, yellow, and orange spectral regions (490-600 nm), resembling the spectral reflectance curve of the abaxial (underleaf) surfaces of green cotton leaves. True blue and white were the most attractive trap base colors for western flower thrips, Frankliniella occidentalis (Pergande), adults. The true blue and white trap bases were moderately high in the blue spectral region (400-480 nm).

Tunable single-frequency radiation in orange spectral region

Sum-frequency mixing of two continuous wave non-planar Nd:YAG ring oscillators (NPROs) at 1064 and 1357 nm have been used to generate tunable, single-frequency radiation at 596 nm. An output power of 16.7 mW was obtained by employing periodically poled KTiOPO4 (PPKTP) as the frequency converter. An absorption curve of iodine vapour was recorded to demonstrate the tunability of this system.

Room-temperature upconversion fiber laser tunable in the red, orange, green, and blue spectral regions

We report continuous-wave tunable laser operation over the 635–637-, 605–622-, 517–540-, and 491– 493-nm wavelength bands in Pr3+/Yb3+-doped ZrF4 –BaF2 –LaF3 –AlF3 –NaF (ZBLAN) optical fiber. A single Ti:sapphire laser is used as the pump source. With as little as 60 mW of pump power launched into the fiber, laser output is obtained over the entire pump-wavelength tuning range of 780 to 880 nm. At a pump wavelength of 860 nm, we have produced output powers of 300 mW at 635 nm (760 mW of launched pump power), 45 mW at 615 nm (430 mW of launched power), 20 mW at 520 nm (200 mW of launched power), and 4 mW at 493 nm (200 mW of launched power).

High performance AlGaInP visible light-emitting diodes

The performance of surface-emitting visible AlGaInP light-emitting diodes (LEDs) is described. The devices have external quantum efficiencies greater than 2% and luminous efficiencies of 20 lm/A in the yellow (590 nm) spectral region. This performance is roughly ten times better than existing yellow LEDs and is comparable to the highest performance red AlGaAs LEDs currently available. The devices also perform favorably compared to existing devices in the orange and green spectral regions. Low-pressure organometallic vapor phase epitaxy (OMVPE) is used to grow the epitaxial layers. The devices consist of a double heterostructure with an AlGaInP active region grown on a GaAs substrate.

The light‐climate of Loch Leven, a shallow Scottish lake, in relation to primary production by phytoplankton

SummarySeasonal changes in incident irradiance and underwater light penetration at Loch Leven from 1968 to 1971 are discussed in relation to the photosynthetic behaviour and crop density of phytoplankton.Light extinction was highest in the blue and lowest in the orange spectral regions, a pattern typical of other turbid waters. Euphotic depth varied between 1·2 and 7·4 m and was on average c. three times the Secchi disc transparency. Underwater light extinction depended chiefly on phytoplankton crop density (estimated as chlorophyll a). Despite the shallowness and wind‐exposed situation of the loch there was no evidence of appreciable light extinction due to sediment disturbance. Possible causes of variability in the relationship between the minimum vertical extinction coefficient (k min) and the concentration of chlorophyll a are discussed.The value of ks, the increment in kmin per unit increment in algal concentration, was estimated from field data as 0·0086 In units per mg chl a/m2 and from laboratory spectroradiometer data as 0·0079 In units per mg chl a/m2. These ks values imply theoretical upper limits for the amount of chlorophyll a in the euphotic zone (Σn max) of 430 and 468 mg chl a/m2, respectively. Observed euphotic chlorophyll a contents (Σn) were sometimes close to these upper limits.Typical photosynthesis/depth profiles are described. Profile area is shown to be related to the logarithm of the ratio between surface‐penetrating irradiance (Io') and the irradiance (Ik) defining the onset of light‐saturation of photosynthesis. Standardized profiles, plotted on a common scale of ‘optical depth’, are used to illustrate the relatively minor influence of variations in Io' and Ik on hourly rates of photosynthesis per unit area.The saturation parameter (Ik) generally increased as photosynthetic capacity (Pmax) increased; the temperature‐dependence of Ik is explained by the temperature‐dependence of the enzyme‐controlled (dark) reactions of photosynthesis, which control Pmax.A spring peak in the ratio between surface penetrating irradiance (Io') and Ik is interpreted as a result of a lag in the seasonal increase in water temperature with increase in surface irradiance.The gradient (K') of the linear light‐limited region of the photosynthesis‐irradiance curve showed little variation and had an average value of 0·31 mg O2/mg chl a.h per 1 W/m2 (PAR).Interactions between mixed depth, underwater light extinction and phytoplankton productivity are discussed; comparisons are made with other shallow, optically deep lakes.