Research Projects

In alignment with global goals for sustainable development and India's initiatives like UJALA and Make in India, the lighting industry is rapidly transitioning toward solid-state lighting (SSL), particularly phosphor-converted LEDs (pc-LEDs). A core challenge in current LED technologies is the so-called “cyan gap”—a spectral hole between 480–520 nm—that compromises full-spectrum human-centric lighting and adversely affects biological systems such as sleep, mood, and circadian rhythm. Therefore, developing phosphors that efficiently emit narrow-band cyan light is vital for advancing full-spectrum and health-friendly lighting. For narrow emission in particular spectra region, the phosphor host with condensed and rigid structure is desired, for with UCr₄C₄ type phosphors have gained special attention. Among this class of materials, a substantial progress is enjoyed by Eu²⁺ activated alkali lithosilicates, offering tunable emission over full visible spectrum, except in “cyan region”. Among various attempts to fill this spectral hole, Eu²⁺ activated alkali lithosilicates results in secondary peaks or broader emissions that compromise spectral purity. Research groups like those of Prof. Huppertz and Prof. Xia have published extensively on Eu²⁺-based phosphors, and companies like OSRAM have commercialized some of them. Despite this, there is very limited exploration of Ce³⁺ in alkali lithosilicates, with only one reported example—NaK₂Li[Li₃SiO₄]₄:Ce³⁺—which yielded emissions at 372–450 nm but lacked control over emission peak width and Ce oxidation state. Thus, the project hypothesizes that red-shifted, narrow cyan emission can be achieved by optimizing the host’s alkali metal composition and Ce doping strategy. As alkali metal choice, literature has suggested the incorporation of Rb⁺/Na⁺ for red-shift in emission and K⁺ for controlling the full width at half maxima. Thus, preset study will be uniquely exploring Ce³⁺ doping in alkali lithosilicate hosts of general formula X[Li₃SiO₄] (where X = Na, K, Rb), with intention towards cost-effective, tunable and valence control emission, owing to earth-abundant precursors, versatility of host upon alkali metal ion combinations and host controlled/oxidation state-controlled emission from Ce, respectively. The phosphors will be synthesized by solid state route, and subsequent study of local electronic structure and luminescence response of the system will be done. The optimized composition will be mixed with other commercial spectral components for its casting as prototype to monitor the emission response, for targeted full-spectrum human-centric lighting backed by various luminescence parameters, such as color rendering index, correlated color temperature, gamut area, luminous efficacy, etc.