Lead-free perovskite Rb2Sn1-xTexCl6 with bright luminescence for optical thermometry and tunable white light emitting diodes

The low photoluminescence (PL) quantum yield (QY) of perovskite Rb2SnCl6 severely limits its commercial development in optics, although it has perfect environmental stability and lead-free toxicity. Here, Te4+ substituted lead-free double perovskite Rb2SnCl6 microcrystals (MCs) are synthesized successfully by using the solvothermal method, which have a bright broad-band emission and large Stokes shift. The band gaps of Rb2Sn1-xTexCl6 calculated by density functional theory (DFT) are close to the corresponding experimental band gaps. It is verified by DFT that partial Te4+ substitution causes the Rb2SnCl6 from the direct band gap to the indirect band gap. Temperature-dependent steady-state and time-resolved PL (TRPL) spectra as well as absorption spectra reveal that the broad-band emission at 560 nm is attributed to self-trapped excitons (STEs). Then, the PL lifetime of Rb2Sn0.95Te0.05Cl6 MCs is first used to measure temperature in a wide temperature range. The maximum value of relative sensitivity (S-R) obtained at the temperature from 355 to 370 K is 4.4% K-1, and the maximum value of absolute sensitivity (S-A) obtained at 320 K is 28.23 ns K-1 from the calculation of the PL lifetime. PL lifetime measurements are not affected by sample size, excitation source power, and whether the luminous centers are uniformly distributed. The calculated data highlights the higher sensitivity optical thermometry of Rb2Sn0.95Te0.05Cl6 MCs. Rb2Sn0.95Te0.05Cl6 MCs combined with a commercial LED chip are successfully fabricated for the white light emitting diode (WLED). The correlated color temperature (CCT) of the WLED can be adjusted from 3582 to 5164 K by controlling the current. In summary, this research shows that Te4+ substituted Rb2SnCl6 double perovskite MCs exhibit great prospects in optical thermometry and tunable solid-state lighting.