Simultaneous bifunctional application of solid-state lighting and ratiometric optical thermometer based on double perovskite LiLaMgWO6:Er3+ thermochromic phosphors

Abstract

Realization of simultaneous, efficient bifunctional application of thermochromic phosphors on light emitting diodes (LEDs) and as ratiometric thermometers is significant. Herein, doped Er³⁺ ions are introduced as an activator into double perovskite LiLaMgWO₆ host lattice. The developed phosphors can be efficiently excited by a near-ultraviolet LED chip and show bright green emission, mainly at 527 and 543 nm, as well as very low thermal quenching. Their chemical stability is studied, demonstrating excellent application potentials. Furthermore, the temperature sensing properties of LiLaMgWO₆:0.01Er³⁺ were analyzed in the wide range of 303-483 K and show a good exponential relationship between ratiometric intensity and temperature (R ² > 0.999), as well as high sensitivity (2.24% K^-1). Such a system not only optimizes the performance in solid light emitting but also provides an excellent platform for designing high-sensitivity optical thermometry.

Fig. 1. (a) Schematic crystal structure of LiLaMgWO₆. (b) XRD patterns of LiLaMgWO₆:x Er³⁺ with x = 0, 0.005, 0.01, 0.02, 0.03, 0.04, and 0.05. (c) Rietveld refinement XRD patterns of LiLaMgWO₆ host and 0.01Er³⁺-activated LiLaMgWO₆ phosphor, respectively.

Fig. 2. (a and b) FESEM of the host and Er³⁺-activated LiLaMgWO₆ phosphor samples, respectively. (c) SEM element mapping of related phosphors. (d) TEM and (e) HRTEM images of the Er³⁺-activated LiLaMgWO₆ phosphor samples under study. (f) The corresponding SAED pattern of studied samples. (g) XPS analysis of the studied samples. (h) UV-vis diffuse reflectance spectra of samples.

Fig. 3. (a) Excitation (λ_em = 543.75 nm) and emission (λ_ex = 378.25 nm) spectra of LiLaMgWO₆:xEr³⁺ samples as indicated. (b) Decay curves of the ⁴S_3/2 level for LiLaMgWO₆:xEr³⁺ particles.

Fig. 4. DFT calculation studies of LiLaMgWO₆ phosphor: (a) band structure and (b) PDOS. (c) The DRS, PLE, PL, and energy level diagrams involved in the energy transfer process from CTB to Er³⁺ in LiLaMgWO₆:Er³⁺ phosphors.

Fig. 5. (a) Thermal quenching behavior of PL emission spectra of LiLaMgWO₆:0.01Er³⁺ phosphors under 378.25 nm excitation in the temperature range from 303 to 483 K. Inset: the visual thermal quenching behavior. (b) Temperature-dependent normalized integrated PL intensities. (c) PL spectra of pristine LiLaMgWO₆:0.01Er³⁺ and samples with different immersion times. Inset: the corresponding visual chemical stability behavior. (d) The dependence of normalized integrated PL intensities as a function of immersion time.

Fig. 6. (a) Normalized green emission spectra of LiLaMgWO₆:0.01Er³⁺ phosphor at various temperatures. (b) FIR value related to temperature. (c) Temperature-dependent PRA as a function of temperature. (d) Sensor sensitivity as a function of temperature in the range of 303–483 K for LiLaMgWO₆:0.01Er³⁺ phosphor.

Fig. 7. EL spectrum of the fabricated green-emitting LED device. (a) Digital images of the fabricated device without and with power input. (b) CIE chromaticity diagram of the LiLaMgWO₆:0.01Er³⁺ materials.