Strategic Investigation of Dual-Mode Light Emission from Tm<sup>3+</sup>/Ho<sup>3+</sup>/Yb<sup>3+</sup>-Activated NaLa(MoO<sub>4</sub>)<sub>2</sub> Phosphors for Color Tunability and Optical Temperature Sensing Applications
Sonali Tomar, Neeraj Kumar Mishra, Vaibhav Chauhan, Kaushal Kumar, C. Shivakumara
Abstract
The development of phosphors with high reliability along with suitable sensitivity ( S r > 1% K –1 ) and thermal resolution (Δ T < 0.5 K) in the physiological temperature range is still a critical challenge for their potential ability in various applications. Adding to the ongoing research, we have studied the nonthermal coupling energy levels of Tm 3+, Ho 3+, and Yb 3+ ions in the tridoped NaLa(MoO 4 ) 2 (NLMO) phosphors. The comparative temperature-dependent upconversion (UC) study of the Tm 3+ /Yb 3+, Ho 3+ /Yb 3+, and Tm 3+ /Ho 3+ /Yb 3+ -doped NLMO phosphors was performed, and maximum relative sensitivity of about 1.63% K –1 (at 308 K) and temperature uncertainty in the range of 0.08–0.26 K are achieved for Tm 3+ /Ho 3+ /Yb 3+ tridoped NLMO phosphor. The repeatability measurements for four cycles validate the excellent thermal stability of the phosphor. The Tm 3+ /Ho 3+ codoped phosphors exhibit excellent energy transfer of about 99% from Tm 3+ to Ho 3+ ions, which results in the color tunability from blue to green region. The excellent energy transfer is well supported by decay analysis. Moreover, the excitation of 358 nm matches well with the commercially available near UV chips. The results of our study on Tm 3+ /Ho 3+ /Yb 3+ -doped NLMO phosphors reveal their potential application as a upconverting temperature sensor and downconverting color tunable phosphors.