White light emitting MgAl2O4:Dy3+,Eu3+ nanophosphor for multifunctional applications

Abstract

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.