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Near-ultraviolet (NUV)-pumped white light-emitting-diodes (WLEDs) often suffer from poor color rendering in the 480-520 nm range, highlighting the need for an efficient cyan phosphor with strong absorption at 370-420 nm. This study presents the successful synthesis of cyan-emitting ZnS/ZnO phosphors using a high-energy planetary ball milling method followed by post-annealing. The fabricated phosphors, with particle sizes ranging from 1 to 3 μm, exhibit strong cyan emission with CIE chromaticity coordinates of (0.2302, 0.3759) and excellent thermal stability with an activation energy of 0.26 eV. A prototype near-ultraviolet (NUV)-pumped cyan LED was developed, achieving chromatic coordinates of (0.2769, 0.4380) and a quantum efficiency of 77% by coating an NUV chip at 370 nm with the synthesized phosphor. These results demonstrate the potential of ZnS/ZnO-based materials as efficient, non-toxic alternatives to rare-earth phosphors, paving the way for advancements in full-spectrum white LEDs for solid-state lighting., Competing Interests: The authors declare no conflict of interest., (This journal is © The Royal Society of Chemistry.)

Phosphor-converted white light-emitting diodes (WLEDs) have received significant attention; however, the leaked light from their blue InGaN chips has an undesirable effect on human health. Hence, it is necessary to develop red, green, and blue-emitting phosphors, which can be excited by an NUV chip instead of a blue chip. Herein, green-emitting ZnO:Cu 2+ phosphors have been successfully synthesized by a simple and facile thermal diffusion method. The obtained powder shows a broad emission band peaking at 525 nm and a strong absorption peak at 377 nm. The ZnO:5%Cu 2+ phosphor annealed at 800 °C in 2 hours revealed a lifetime of 0.57 ms, an activation energy of 0.212 eV, and the highest emission intensity with ( x , y ) CIE colour coordinates (0.3130, 0.5253). A WLED prototype has been fabricated by coating the ZnO:5%Cu 2+ phosphor on an NUV 375 nm LED chip, where this coated phosphor shows a high quantum efficiency (QE) of 56.6%. This is, so far, the highest reported QE value for ZnO-based phosphors. These results suggest that the ZnO:Cu 2+ phosphor could be an excellent candidate for NUV-pumped phosphor-converted WLED applications.

Eu 3+ -doped phosphors have been much attractive owing to their narrow-band red emission peak at 610-630 nm with high color purity; however, the weak and narrow absorption band in the NUV region limits their applications. Doping a higher amount of Eu 3+ ions into a non-concentration quenching host could be key to enhancing the efficiency of the absorption value and emission intensity. Hence, the design of Eu 3+ -heavily doped phosphors with a suitable host lattice is key for applications. In this study, red-emitting Eu 3+ -doped Gd(BO 2 ) 3 -Y 3 BO 6 -GdBO 3 (GdYGd:Eu 3+ ) phosphor with a high quantum efficiency of 58.4% and excellent color purity of 99.5% is reported for the first time. The phosphor is efficiently excited by NUV light at 394 nm and emits a strong red emission band in the 590-710 nm range, peaking at 612 nm. The optimal annealing temperature and Eu 3+ doping content to obtain the strongest PL intensity are 1100 °C and 20 mol%, respectively. The optimized GdYGd:Eu 3+ phosphor possesses a high activation energy of 0.319 eV and a lifetime of 1.14 ms. An illustration of phosphor-coated NUV LED with chromaticity coordinates ( x = 0.5636, y = 0.2961) was successfully synthesized, demonstrating the great potential of GdYGd:Eu 3+ phosphor for NUV-pumped WLED applications., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

We study phase transition properties of the two-dimensional q-state clock model by an extensive Monte Carlo simulation. By analyzing the Binder ratio and its temperature derivative, we confirm that the two-dimensional q-state clock model exhibits two distinct Kosterlitz-Thouless phase transitions for q=5,6 but it has one second-order phase transition for q=4. The critical temperatures are estimated quite accurately from the crossing behavior of the Binder ratio (for q<5) and from negative divergent dips of the derivative of the Binder ratio (for q≥5) around these critical points. We also calculate the correlation length, the helicity modulus, and the derivative of the helicity modulus, and analyze their behaviors in different phases in detail.