Comparative study on visible-infrared and upconversion luminescence of Er3+,Yb3+ Co-doped La2Zr2O7 and Y2Zr2O7 phosphors for optical thermometry and latent fingerprint detection

Abstract

This study presents a comprehensive comparison of the structural and optical characteristics of rare-earth activated La₂Zr₂O₇ (LZO) and Y₂Zr₂O₇ (YZO) phosphors, each being synthesized by both the combustion method (CMB) as well as the microwave hydrothermal (MHT) method. The structural characterization confirmed the successful formation of both compounds without impurity phases. The optical characterization studies, including photoluminescence (PL) under UV excitation and upconversion photoluminescence (UCPL) under 980 nm and 1550 nm laser excitation, reveal distinct luminescent properties. Under 378 nm excitation, both phosphor systems exhibit emissions spanning the visible (500–725 nm) and near-infrared (900–1600 nm) regions, with peak intensities at 545 nm, 980 nm, and 1530 nm. The UCPL results shows enhanced green emission for Er³⁺,Yb³⁺ co-doped LZO and red emission for Er³⁺,Yb³⁺ co-doped YZO upon 980 nm laser excitation. Under 1550 nm laser excitation, the Er³⁺-doped samples exhibit superior luminescence compared to Er³⁺,Yb³⁺ co-doped counterparts. Optical thermometry studies indicate that the LZO:Er³⁺,Yb³⁺ sample prepared by MHT method achieved a maximum absolute sensitivity of 54 × 10⁻⁴ K⁻¹ at 393 K and 30.7 × 10⁻⁴ K⁻¹ at 313 K for 980 nm, 1550 nm laser excitations, respectively. Similarly, the YZO:Er³⁺,Yb³⁺ sample prepared by the CMB method achieved a maximum absolute sensitivity of 22 × 10⁻⁴ K⁻¹ at 433 K and 17.2 × 10⁻⁴ K⁻¹ at 353 K for 980 nm, 1550 nm laser excitations, respectively. Besides optical thermometry studies, the brightest sample, LZO:Er³⁺,Yb³⁺ synthesized via MHT method, demonstrated strong green luminescence under 980 nm laser excitation, offering potential for latent fingerprint detection applications.