Feeble white emission with a low Colour Rendering Index (CRI) has become the principal gridlock for the extensive commercialization of phosphor converted white LEDs (pc-WLEDs). Fusion of red, green and blue emitting rare-earth (RE) ions in a suitable host can overcome these drawbacks but the energy migration between multiple RE ions at single excitation wavelength defines the key standpoint in designing such white light emitting phosphors. Apart from the abovementioned obstacles, recently traditional optical temperature sensors based on RE ions have faced difficulties due to their low relative sensitivity and large detection error. Keeping these points in mind, in this work, a series of MgAl2O4:Dy3+,Eu3+ nanophosphors are synthesized among which 2% Dy3+,0.2% Eu3+ doped MgAl2O4 nanophosphors demonstrate strong white emission with CIE co-ordinates of (0.31, 0.33), and high quantum yield (∼67%), which could be directly utilized for pc-WLED based solid state lighting devices. Detailed investigation of PL properties reveals that Eu3+ ions can be well sensitized by Dy3+ under near-ultraviolet excitation of 351 nm. Dexter's theory & Reisfeld's approximation are employed for an in-depth analysis of the inter-RE energy transfer (ET) mechanism, which signposts that the dipole-quadrupole interaction phenomenon is responsible for the ET process from Dy3+ to Eu3+. Additionally, the validated ET plays a pivotal role in demonstrating the self-referencing ratiometric temperature sensor behaviour supported by a distinct high temperature thermal quenching trend between Dy3+ and Eu3+ ions. Hence the obtained nanophosphors are highly promising for utilizing in WLED based solid state lighting and self-referencing ratiometric temperature sensor applications.
Lead halide perovskite nanocrystals (NCs) have recently
emerged
as cutting-edge semiconductor materials for the development of optoelectronic
devices. Exploitation of delayed hot carrier (HC) relaxation is an
effective way to increase the solar conversion efficiency further.
Therefore, delaying the HC relaxation time is essential. Here, we
have reported a simple strategy to passivate the surface of CsPbX3 (X = Br/Cl) NCs with hexadecylamine (HDA) molecules, followed
by exploitation of the femtosecond transient absorption spectroscopic
information to determine the HC relaxation dynamics and ultrafast
carrier dynamics. Faster ultrafast carrier relaxation dynamics are
observed with the increasing Cl content in the CsPbX3 NCs
(X = Br/Cl). Furthermore, we proposed slower ultrafast carrier relaxation
dynamics along with longer HC relaxation time in the HDA-passivated
CsPbX3 (X = Br/Cl) NCs compared to the pristine NCs. The
substantial increase in the initial HC temperature and a prolonged
HC decay time additionally reveal the effective delay in HC cooling
dynamics after the passivation of the NCs with HDA molecules. A thorough
understanding of the charge-carrier relaxation dynamics in CsPbX3 (X = Br/Cl) NCs will provide a way to design efficient optoelectronic
devices.
In recent years, nanoscale phosphors have become vital in optoelectronic applications and to understand the improved performance of nanophosphors over bulk material, detailed investigation is essential. Herein, trivalent europium-activated Y4Al2O9 phosphors were developed by solid-state reaction and solvothermal reaction methods and their performance as a function of their dimension was studied for various applications. Under 394 nm optical excitation, the photoluminescence (PL) emission, excited state lifetime of the nanophosphor, exhibits greater performance than its bulk counterpart. The homogeneous spherical structure of the nanophosphors as compared with solid lumps of bulk phosphors is the basis for almost 40% of the enhancement in nanophosphors' intense red emission compared to the bulk. Moreover, the thermal stability of the nanophosphor is much better than the bulk phosphor, which clearly indicates a key advantage of nanophosphor. The superior performance of Eu3+-doped Y4Al2O9 nanophosphors over their bulk counterparts has been demonstrated for industrial phosphor-converted light-emitting diodes and visualization of latent fingerprint.
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