Emission characteristics of inorganic/organic hybrid white-light phosphor

A white-light light-emitting diode (LED) was successfully fabricated by converting near-UV LED emission (390–420 nm) with a new inorganic/organic hybrid phosphor. This new white-light phosphor consisted of three fluorescence materials; two strontium aluminates based with lanthanide oxides, SrAl₂O₄:Eu²⁺ (for green (520 nm) emission) and Sr₄Al₁₄O₂₅:Eu²⁺ (for blue (490 nm) emission) and a new organic Eu metal complex, Eu(BTFA)₃phen (for red (614 nm) emission). These materials have good absorption in the 300–500-nm range and have high quantum efficiencies (4.7–24.5%). The white phosphor has a CIE value of (0.321, 0.365). PACS 42.70.-aj; 78.40.-q; 78.55.-m; 81.05.Lg     

Suppressed speckle contrast of blue light emission out of white lamp with phosphors excited by blue laser diodes for high-brightness lighting applications

The speckle contrast of blue light emission out of high-brightness white lamps using phosphors excited by InGaN/GaN blue laser diodes is evaluated as a measure of coherence. As a result, speckle contrast of as low as 1.7%, the same level as a blue light emitting diode, is obtained. This implies that the original blue laser light can be converted into incoherent light through lamp structures without any dynamic mechanisms. This unique speckle-free performance is considered to be realized by multiple scattering inside the lamp structure, the multi-longitudinal mode operation of the blue laser diodes, and the use of multiple laser diodes. Such almost-incoherent white lamps can be applied for general lighting without any nuisance of speckle noise and should be categorized as lamps rather than lasers in terms of laser safety regulation.     

Upconversion white-light emission in Ho3+/Yb3+/Tm3+ codoped LiNbO3 polycrystals

Ho³⁺/Yb³⁺/Tm³⁺ codoped LiNbO₃ polycrystals exhibiting upconversion white-light under 980 nm excitation have been successfully fabricated by the high temperature solid-state reaction method. CIE coordinate of the Ho³⁺/Yb³⁺/Tm³⁺/LiNbO₃ polycrystal is (0.34, 0.35), which is very close to the standard equal energy white-light illuminate (0.33, 0.33). Efficient green, red, and blue upconversion emissions have been observed. The luminescent decay dynamics are studied, and rate equations for the blue, green, and red emissions are set up to analyze the upconversion luminescence mechanism. The present results demonstrate that the competition between the linear decay and the upconversion process for the depletion of the intermediate excited states plays an important role in upconversion mechanism. The LiNbO₃ with upconversion white-light will be a promising luminous material.     

激光激励下镝离子掺杂氟硼酸盐玻璃荧光体的辐照参数

采用高温熔融法制备了镝离子掺杂氟硼酸盐玻璃荧光体,利用积分球绝对光谱测试系统,在453 nm蓝色激光二极管激发下,对玻璃荧光体的荧光光谱进行表征,解析出玻璃荧光体的相关绝对荧光参量。测试与计算结果表明,1.0 Wt% Dy₂O₃掺杂玻璃荧光体在功率15.81 mW的蓝色激光激发下,净发射光谱功率是286.91 μW,发射光子数为17.17×1014 cps,其荧光量子产率达到25.86%。为提高玻璃荧光体对泵浦激光的利用率,减少残余激光成分,进而改善组合光品质,制备了大体积的1.5 Wt% Dy₂O₃掺杂玻璃荧光体,在高功率的蓝色激光激发下获得白色照明效果,该玻璃荧光体在激发功率分别为56.0和252.7 mW的激光激发下,组合荧光对应的色坐标分别是(0.316, 0.287)和(0.303,0.268)。激光激励下的高效白色发光表明Dy3+掺杂氟硼酸盐玻璃荧光体在激光照明领域具有良好的应用前景。     

Diode-laser-pumped continuous-wave doubly linear resonator sum-frequency mixing red laser at 689 nm

We report for the first time a coherent red radiation at 689 nm by intracavity sum-frequency generation of the 1319- and 1444-nm laser-lines of two Nd:YAG lasers. Using type-II critical phase matching KTP crystal, 689-nm red laser was obtained by 1444- and 1319-nm intra-cavity sum-frequency mixing, and output power of 156 mW was obtained. At the output power level of 156 mW, the output power stability is better than 5.0% and laser beam quality M ² factor is 1.23.     

White up-conversion emission in Ho/Tm/Yb tri-doped glass ceramics embedding BaF2 nanocrystals

Ho³⁺/Tm³⁺/Yb³⁺ tri-doped glass ceramics with white light emitting have been developed and demonstrated. Pumped by 980 nm laser diode (LD), intensive red, green and blue up-conversions (UC) were obtained. The green emission is assigned to Ho³⁺ ion and the blue emission is assigned to Tm³⁺ ion, whereas the red emission is the combination contribution of the Ho³⁺ and Tm³⁺ ions. The RGB intensities could be adjusted by tuning the rare-earth ion concentration and pump power intensity. Thus, multicolor of the luminescence, including perfect white light with CIE-X=0.329 and CIE-Y=0.342 in the 1931 CIE chromaticity diagram can be obtained in 0.15 Ho³⁺/0.2Tm³⁺/3Yb³⁺ tri-doped glass ceramics embedding BaF₂ nanocrystals pumped by a single infrared laser diode source of 980 nm at 500 mW. The up-conversion luminescence mechanism of Yb³⁺ sensitize Ho³⁺ and Tm³⁺ ions and the energy transfer from Ho³⁺ to Tm³⁺ in oxy-fluoride silicate glass ceramics were analyzed.     

Out of the blue: semiconductor laser pumped visible rare‐earth doped lasers

The rise of semiconductor‐based pump sources such as In_xGa_1‐xN‐laser diodes or frequency‐doubled optically pumped semiconductor lasers with emission wavelengths in the blue encourages a revisitation of the rare‐earth ions Pr³⁺, Sm³⁺, Tb³⁺, Dy³⁺, Ho³⁺ and Er³⁺ with respect to their properties as active ions in crystalline solid‐state laser materials with direct emission in the visible spectral range. Nowadays, some of these blue‐pumped visible lasers compete with Nd³⁺‐lasers in terms of efficiency and direct lasing at various colors from the cyan‐blue to the deep red can be addressed in very simple and compact laser setups. This paper highlights the spectroscopic properties of suitable rare‐earth ions for visible lasing and reviews the latest progress in the field of blue‐pumped visible rare‐earth doped solid‐state lasers.

     

Upconversion white-light emission in Ho³⁺/Yb³⁺/Tm³⁺ tridoped LiNbO₃ single crystal

Ho³⁺/Yb³⁺/Tm³⁺ tridoped LiNbO₃ single crystal exhibiting intense upconversion white light under 980?nm excitation has been successfully fabricated by the Czochralski method. The tridoped LiNbO₃ single crystal offers power dependent color tuning properties by simply changing excitation power. Efficient three-photon blue upconversion emission and two-photon green and red upconversion emissions have been observed. In addition, the red emission of Ho³⁺ originates dominantly from the nonradiative decay of green emission. The LiNbO₃ with upconversion white light will be a potential laser candidate material.     

A novel Dy3+-doped GdPO4 white-light phosphors under vacuum ultraviolet excitation for Hg-free lamps application

Novel Dy3+-doped GdPO4 white light phosphors with monoclinic system were successfully synthesised by hydrothermal method at 240 ℃. This paper investigates the luminescence properties of white-light Gd1-xPO4 : xDy3+ under vacuum ultraviolet (VUV) excitation. The strong absorption at around 147 nm in excitation spectrum energy can be transferred to the energy levels of Dy3+ ion from the host absorption. Additionally, this white light phosphors are activated by a single Dy3+ ion and with a lower preparation temperature, which tend to decrease the consumption of rare earth resource and energy. Therefore, the luminescence of Gd1-xPO4 : xDy3+ under VUV excitation is effective, and proves to be promising in application to mercury-free lamp.     

Blue diode pumped solid-state lasers for digital projection

Lasers present many advantages over currently used light sources for projection applications. Compact as well as efficient displays can be realized with RGB laser systems. The extreme brightness and collimation of lasers enable very efficient light collection. For portable, battery-powered microprojectors or even integrated devices, where the efficiency becomes even more critical, 50 mW per color is enough for a luminous flux on the projection screen of 20 lm. While blue and red diode lasers in this power range are becoming widely available, the bottleneck for this application is still the lack of integrated green laser sources. We present here a blue-diode pumped Pr³⁺-doped LiYF laser emitting at 523 nm. By optimizing on many aspects of the crystal and resonator, we increased the laser output power up to 169.4 mW, which corresponds to a total power conversion efficiency of 7%. Moreover, lasing in red can be obtained with the same crystal with similar or even better output powers. This makes the Pr:YLF laser an ideal candidate for an RGB projection source together with blue InGaN diodes.     

Red-enhanced white light-emitting diodes using external AlGaInP epilayers with various aperture ratios

A novel hybrid white light-emitting diode (LED) is proposed to enhance the red color and stability of the chromaticity under various operating currents using an AlGaInP photon-recycling (PR) epilayer. A blue/yellow white InGaN LED sample is covered with an external patterned AlGaInP epilayer. Under an optimum aperture ratio of 30%, the luminous efficiency of the PR-LED lamp can achieve a color coordinate of (x=0.340, y=0.295). When the injection current increases from 50 to 350 mA, the color temperature decreases from 4030 to 3700 K and the color rendering index increases from 81 to 86. These could be due to the fact that the AlGaInP epilayer was not attached onto the LED chip, alleviating the thermal effect on the color coordinate. The present white PR-LED samples have high potential for portable liquid-crystal-display backlight applications.     

KBaBP2O8:Tm3+: a novel blue-emitting phosphor with high color purity

A series of novel blue emitting K_{1 + x} Ba_{1 ? 2x} Tm _x BP₂O₈ (0.01 ≤ x ≤ 0.08) phosphors were synthesized by a solid-state reaction at a high temperature for the first time. The phase purity and photoluminescence properties were investigated by X-ray diffraction (XRD) and fluorescence spectroscopy (FS) measurements, respectively. The influence of the doping concentration of Tm³⁺ on its relative emission intensity was investigated, and the critical distance was calculated. The as-prepared phosphor can be effectively excited with a 356-nm light, and exhibit blue emission at 457 nm with high color purity. The above work indicates this phosphor could be a potential candidate as blue emitting phosphor for application in white light-emitting diodes.     

Comparison of surface films formed on titanium by pulsed Nd:YAG laser irradiation at different powers and wavelengths in nitrogen atmosphere

The nitridation of titanium (Ti) caused by a Q-switched Nd:YAG laser under nitrogen gas atmosphere was investigated in situ using X-ray photoelectron spectroscopy (XPS). A laser having a wavelength of 1064 nm and 532 nm (SHG mode) was irradiated on a titanium substrate in an atmosphere-controlled chamber, and the substrate was then transported to an XPS analysis chamber without exposing it to air. The characteristics of the surface layer strongly depend on the laser power. When the power is relatively low, a titanium dioxide layer containing a small amount of nitrogen is formed on the substrate. Laser irradiation beyond a certain laser power is required to obtain a stoichiometric titanium nitride (TiN) layer. A TiN layer and an oxynitride layer with a TiO_xN_y-like structure are formed as the topmost and the lower surface layer, respectively, when the laser power exceeds this threshold value. The threshold laser power strongly depends on the wavelength of the laser, and this threshold value for the 532-nm laser is quite lower than that for the 1064-nm laser.     

The luminescence properties of Dy3+-activated SrB4O7 under VUV excitation

Dy³⁺-doped SrB₄O₇ phosphors were synthesized by solid-state reaction. The luminescence properties of white-light SrB₄O₇:Dy³⁺ under vacuum ultraviolet (VUV) excitation were firstly investigated. According to strong absorption around 147 nm in excitation spectra, energy can easily be transferred to the energy levels of Dy³⁺ from host absorption, and hence luminescence of SrB₄O₇:Dy³⁺ under VUV excitation was effective, and it has the potential of being applied to a white lamp-house for mercury-free lamp.     

Simple-structure white organic light emitting diodes with high color temperature

We present high color temperature white organic light emitting diodes with a simple p-i-n structure. A sky blue phosphorescent dopant of iridium(III) bis[4,6-(difluorophenyl)-pyridinato-N,C^2’] picolinate and a red phosphorescent dopant of bis(2-phenylquinoline)(acetylacetonate)iridium(III) in the emissive layers is employed to make high color temperature devices. Very stable color variation under ?0.02 until a 5000 cd/m² brightness value is realized by efficient carrier control in a multi stacked emitting layer of blue/red/blue colors. Maximum current and power efficiencies of 23.8 cd/A and 22.9 lm/W in forward direction are obtained. With balanced emissions from the two emitters, the white light emission with very high correlated color temperature of 7308 K as well as CIE coordinates of (0.30, 0.33) is achieved.     

β-NaGd_(0.794)Yb_(0.200)Ho_(0.001)Tm_(0.005)F_4纳米颗粒的白色上转换发光

利用简单的水热合成法制备了β-NaGd0.794Yb0.200Ho0.001Tm0.005F4纳米颗粒。采用X射线粉末衍射(XRD)技术测定了样品的物相,结果显示样品为六角相。通过透射电子显微镜(TEM)和高分辨透射电子显微镜观察的结果样品为椭球和六角形状,颗粒的平均尺寸为23 nm。用980 nm半导体激光二极管为激发光源,测定了样品的室温上转换发射谱,结果表明:样品分别发射红、绿和蓝色光,其相对发射强度,从强到弱的顺序为蓝色、绿色和红色,与其对应辐射跃迁分别为Tm3+离子的1G4→3H6,Ho3+离子的5F4→5I8,5F5→5I8跃迁。样品发射的蓝、绿和红光组合而发出强的白色上转换发光,其色品坐标为(x=0.271 7,y=0.267 3)。     

456-nm deep-blue laser generation by intracavity frequency doubling of Nd:GdVO4 under 879-nm diode pumping

We report on a simple, compact continuous-wave 456-nm laser by intracavity frequency doubling of an end-pumped Nd:GdVO₄ laser on the ⁴ F _3/2 → ⁴ I _9/2 transition. A 5-mm-long, 0.2-at % Nd:GdVO₄ bulk crystal is employed as the gain medium and the Nd³⁺ ion is directly pumped into the emitting level (⁴ F _3/2) by a novel 879-nm laser diode. Intracavity frequency doubling with a 15-mm-long LBO crystal and a 10-mm-long BiBO crystal in a linear cavity yield 56- and 118-mW single-ended blue outputs at the absorbed pump power of 11.9 W, respectively. The corresponding values are scaled to 286 and 391 mW, respectively, in a V-type cavity, with optical conversion efficiencies of 2.4 and 3.3% versus the absorbed pump power. The fluctuations of the 456-nm output power for both cases are less than 3% at the maximum output level.     

Pulsed mercury capillary lamps for dye laser pumping: Spectral measurements

Calibrated spectral measurements of the light emitted by a pulsed high-pressure mercury capillary lamp are presented. These pulsed lamps have been used in a previous work to pump a Rhodamine 6G laser. The measurements presented here show a very high efficiency in the blue and near UV part of the spectrum, suggesting that these lamps represent a very attractive pumping source for dye lasers emitting in the blue. In particular, as an example, a computation has been made for a basic solution of 4-MU yielding a spectral efficiency of 24%.     

Multicolor upconversion emission from Tm3++Ho3++Yb3+ codoped tellurite glass on NIR excitations

Multicolor emission has been produced using 798 nm and 980  nm laser excitation in a Tm³⁺+Ho³⁺+Yb³⁺ codoped tellurite based glass. This glass generates simultaneously red, green and blue (RGB) emission on 798 nm excitation. Multicolor emission thus obtained was tuned to white luminescence by adjusting the Ho³⁺ ion concentration. There is a close match between the calculated color coordinate for the white luminescence obtained here and the point of equal energy which represents white in the 1931 CIE chromaticity diagram. The 980 nm excitation of the same sample on the other hand gives intense green and red emission and the glass appears greenish.