Al2O3-YAG:Ce composite ceramics for high-brightness lighting

High luminous efficiency and excellent thermal performance in rod-shaped YAG:Ce phosphor ceramics for laser lighting

High power and high brightness laser lighting puts forward new requirements for phosphor converters such as high luminous efficiency, high thermal conductivity and high saturation threshold due to the severe thermal effect. The structure design of phosphor converters is proposed as what we believe to be a novel strategy for less heat production and more heat conduction. In this work, the rod-shaped YAG:Ce phosphor ceramics (PCs) and disc-shaped YAG:Ce PCs as control group were fabricated by the gel casting and vacuum sintering, to comparatively study the luminescence performance for LD lighting, on the premise that the total number of transverse Ce3+ ions and the volume of samples from two comparison groups were same. All rod YAG:Ce PCs with low Ce3+ concentration exhibited the high luminous efficiency and better thermal stability than YAG:Ce discs with high Ce3+ concentration. Under the laser power density of 47.8 W/mm2, the luminous saturation was never observed in all rod-shaped YAG:Ce PCs. The high luminous efficacy of 245∼274 lm/W, CRI of 56.3∼59.5 and CCT of 4509∼4478 K were achieved. More importantly, due to the extremely low Ce3+ doping concentration (0.01 at%), rod-shaped ceramics based LDs devices showed the excellent thermal performance and their surface temperatures were even below 30.5 °C surprisingly under the laser power density of 20.3 W·mm-2 (2 W). These results indicate that the rod shape of phosphor converter is a promising structure engineering for high power laser lighting.

Al2O3-YAG:Ce/YAG composite ceramic phosphor in a transmissive configuration for high-brightness laser-driven lighting

High-power, high-brightness laser lighting promotes new requirements for light-conversion materials, such as high thermal conductivity, high saturation threshold and compact encapsulation. In this paper, we designed and fabricated a novel composite structure ceramic including a 1.0 × 1.0 mm² Al₂O₃-YAG:Ce ceramic and a φ=16.0 mm transparent YAG ceramic for the transmissive configuration in laser lighting. When pumped by blue laser from 0∼60 W mm², all the samples exhibited no luminous saturation phenomenon, and the 10.0 wt.%Al₂O₃-YAG:Ce/YAG composite ceramic with the thickness of 0.3 mm maintained white light with a luminous efficacy over 200 lm/W. Moreover, a maximal luminous flux over 1000 lm, a correlated color temperature (CCT) of 5471 K, and an operating temperature as low as 92.3 °C were obtained under the excitation power density as high as 60 W/mm². The configuration that Al₂O₃-YAG:Ce encapsulated by YAG reflects an excellent optical and thermal properties by using transparent and highly thermally conductive YAG materials. These results indicate that Al₂O₃-YAG:Ce/ YAG composite ceramic phosphor is a promising candidate in transmissive configuration for automotive lighting and laser searchlight.

Broadband emission Gd3Sc2Al3O12:Ce3+ transparent ceramics with a high color rendering index for high-power white LEDs/LDs

The discovery of single structure Ce³⁺ doped garnet transparent ceramics (TCs) with a broad full width at half maximum (FWHM) is essential to realize a high CRI for high-power white light emitting diodes (LEDs) and laser diodes (LDs). In this work, by utilizing the ion substitution engineering strategy, pure phase Gd₃Sc₂Al₃O₁₂:Ce³⁺ (GSAG:Ce) TC with a broad FWHM of 132.4 nm and a high CRI value of 80.7 was fabricated through the vacuum sintering technique for the first time. The optimized in-line transmittance of TCs was 58.4% @ 800 nm. Notably, the GSAG:Ce TCs exhibited a remarkable red shift from 546 nm to 582 nm, with a high internal quantum efficiency (IQE) of 46.91%. The degraded thermal stability in Ce:GSAG TCs was observed compared with that of Ce:YAG TC, owing to the narrowed band gap of GSAG. Additionally, remote excitation white LEDs/LDs were constructed by combining GSAG:Ce TCs with blue LED chips or laser sources. A tunable color hue from yellow to shinning white was achieved in white LEDs, whereas the acquired CRI and CCT of the white LDs were 69.5 and 7766 K, respectively. This work provides a new perspective to develop TCs with high CRI for their real applications in high-power white LEDs/LDs.

TiO2-SrTiO3 Biphase Nanoceramics as Advanced Thermoelectric Materials

The review embraces a number of research papers concerning the fabrication of oxide thermoelectric systems, with TiO2-SrTiO3 biphase ceramics being emphasized. The ceramics is particularly known for a two-dimensional electron gas (2DEG) forming spontaneously on the TiO2/SrTiO3 heterointerface (modulation doping), unlike ordinary 2DEG occurrence on specially fabricated thin film. Such effect is provided by the SrTiO3 conduction band edge being 0.40 and 0.20 eV higher than that for anatase and rutile TiO2, respectively. That is why, in the case of a checkered arrangement of TiO2 and SrTiO3 grains, the united 2D net is probably formed along the grain boundaries with 2DEG occurring there. To reach such conditions, there should be applied novelties in the field of ceramics materials science, because it is important to obtain highly dense material preserving small (nanoscale) grain size and thin interface boundary. The review also discusses some aspects of reactive spark plasma sintering as a promising method of preparing perovskite-oxide TiO2-SrTiO3 thermoelectric materials for high-temperature applications.