Phosphors For Solid State Lighting Applications Research Articles

Quantum efficiency and energy transfer processes in rare-earth doped borate glass for solid-state lighting

Sm3+, Eu3+ and Tb3+ doped borate glass is investigated for its potential as light converting phosphor for solid-state lighting applications. Concentration-dependent luminescence, quantum efficiency and radiative lifetimes are analysed. The luminescence quantum efficiency exceeds values of more than 80%. Cross-relaxation processes in the single-doped glasses result in luminescence quenching for Sm3+ with increasing doping level, whereas for Eu3+ and Tb3+ an increase is observed. In Sm3+/Eu3+ and Tb3+/Eu3+ double-doped glass the energy transfer processes between the rare-earth ions are investigated in detail. The colour coordinate of the Tb3+/Eu3+ double-doped glass can be shifted from the green to the red spectral range by changing the Tb3+-to-Eu3+ ratio in favour of Eu3+. In addition, double doping allows for a change in colour coordinate by using different excitation wavelengths.

White-light emission of Ca2La8(GeO4)6O2: Tb3+/Sm3+ nanocrystalline phosphors for solid-state lighting applications

Tb3+/Sm3+ ions co-doped Ca2La8(GeO4)6O2 (CLGO) phosphors are prepared by a pechini-type sol–gel technique. The nanocrystalline phosphors are characterized by X-ray diffraction, Fourier transform infrared spectroscopy, and transmission electron microscopy. The photoluminescence emission and excitation spectra are measured for Tb3+, Sm3+ ions single-doped and Tb3+/Sm3+ ions co-doped phosphor samples individually. For the Tb3+/Sm3+ ions co-doped samples, we can observe emission covering the entire visible region with sharp peaks in the green, orange, and red regions. As the Sm3+ ion concentration increases, the Commission International de I'Eclairage chromaticity coordinates shift towards warm white-light region due to the energy transfer from Tb3+ to Sm3+ ions. This energy transfer property is clearly observable in the emission spectra under 374nm excitation.

Full-color-emitting CaYAl3O7:Pr3+,Ce3+ phosphor for near-UV LED-based white light

A full-color-emitting phosphor, CaYAl3O7:Pr3+,Ce3+ was synthesized through conventional solid-state reaction. The structural properties of the phosphor were analyzed by Rietveld refinement, maximum entropy method, and luminescent properties were analyzed by co-activating with different rare earth ions. Photoluminescence spectra on excitation with 450nm source were dominated by green band at 490nm originating from 3P0→3H4 transition of Pr3+ ions and less intense band at 617nm due to 1D2→3H4 transition. On codoping with Ce3+, phosphor exhibits an additional broad band originating from 5d1→4f1 (2F7/2 and 2F5/2) of Ce3+, centered at around 540nm due to efficient energy transfer from Pr3+ levels to Ce3+ levels. With this emission property we recommend CaYAl3O7:Pr3+,Ce3+ as potential single-phase full-color-emitting phosphor for solid-state lighting applications.

Solvothermal synthesis of red and green emitting Ca1.65Sr0.35SiO4:Eu3+ and Ca1.65Sr0.35SiO4:Eu2+ phosphors for solid-state lighting applications

A novel and facile synthetic approach has been trialed, and attempted with success in the preparation of two phosphors namely, a red emitting CaSrSiO4:Eu3+ and a green emitting CaSrSiO4:Eu2+. These phosphors were successfully synthesized using a simple co-precipitating solvo-thermal strategy wherein tetraethyl orthosilicate (TEOS) as silica source and the acetate precursors of strontium (Sr2+), calcium (Ca2+) and europium (Eu3+) are utilized. The material so obtained is subjected to an extensive photoluminescence behavior study. The concentration of the dopant (Eu3+and Eu2+) plays a significant role in the determination of photoluminescence behavior and hence a systematic and in-depth experimental studies were done and the results are synchronized. On interpretation of the output, it came to light that an intense emission signals sparked in the red region (590 and 615nm) in the case of phosphor doped with Eu3+, which is excited under near ultra violet (395nm) and blue (466nm) region. In case of the CaSrSiO4 sample doped with Eu2+, an intense broad green signal (~510nm) is obtained under the excitation range of 350–430nm. The results obtained are quite encouraging and made a strong confirmation as, the solvo-thermally synthesized CaSrSiO4, which is activated by the dopants namely Eu3+ and Eu2+ possesses an immense potential and it is exactly tapped by the adopted methodology. Despite its strong impact, it will also assure a strong revolution in the fabrication and thus the commercialization of white LEDs as both the red and green emitting phosphor.

Thermally Activated Degradation of Remote Phosphors for Application in LED Lighting

This paper reports on an extensive analysis of the degradation of remote phosphors for solid-state lighting applications. The study is based on combined optical and thermal measurements, carried out before and during long-term stress tests, and provides the following results: 1) During normal operation, phosphors can show significant self-heating; 2) as a consequence of self-heating, the conversion efficiency of the phosphors decreases; and 3) exposure to long-term stress tests at moderate/high temperature levels (in the range of 85 °C-145 °C) can lead to remarkable degradation of the phosphors. Degradation mainly consists in a decrease in conversion efficiency and in worsening of the chromatic properties of the light-emitting diode-phosphor system. Finally, an activation energy value of 1.2 eV was extrapolated for the thermally activated degradation of the phosphors.

PL25 Non-coherent light sources in the blue range of the spectrum for treating streptostaphylodermias

A full-color-emitting phosphor, CaYAl3O7:Pr3+,Ce3+ was synthesized through conventional solid-state reaction. The structural properties of the phosphor were analyzed by Rietveld refinement, maximum entropy method, and luminescent properties were analyzed by co-activating with different rare earth ions. Photoluminescence spectra on excitation with 450 nm source were dominated by green band at 490 nm originating from 3P0→3H4 transition of Pr3+ ions and less intense band at 617 nm due to 1D2→3H4 transition. On codoping with Ce3+, phosphor exhibits an additional broad band originating from 5d1→4f1 (2F7/2 and 2F5/2) of Ce3+, centered at around 540 nm due to efficient energy transfer from Pr3+ levels to Ce3+ levels. With this emission property we recommend CaYAl3O7:Pr3+,Ce3+ as potential single-phase full-color-emitting phosphor for solid-state lighting applications.

Synthesis and luminescence properties of SrBPO 5:Eu 2+, Mn 2+ phosphor for light-emitting diodes

Motivated by the need of new phosphors for solid-state lighting applications, Eu 2+, Mn 2+-doped SrBPO 5 was prepared by solid-state reaction and its photoluminescence properties were investigated. The excitation band of the phosphors covers wide region from 300 to 410 nm, which can be excited effectively by InGaN chip. The emission band consists of two peaks located at 433 and 509 nm, respectively. Adjusting the content of Eu 2+ and Mn 2+ could result in color-coordinate parameters x, y changing regularly, and lighting color moves from blue to blue-white. The experimental results show that SrBPO 5:Eu 2+, Mn 2+ is a promising single host phosphor to use in white light emitting diode (WLED).