Five-level anti-counterfeiting based on versatile luminescence of tri-doped double perovskites

Luminescent materials with multi-emission features are difficult to be replicated, which are highly desirable for advanced anti-counterfeiting. Here, we report the pioneering synthesis of Mn^(2+)/Yb^(3+)/Er^(3+) tri-doped Cs2Ag0.8Na0.2InCl6 double perovskites (MYE-DP), which exhibit photoluminescence (PL) covering from visible to near-infrared (NIR). The PL colors under excitations of 254 and 365 nm are notably different due to the changed relative emission intensities of self-trapped excitons (STEs) and Mn^(2+) d–d transition. Moreover, under the excitation of a NIR laser, the MYE-DP exhibits upconversion (UC) emissions of Mn^(2+) and Er^(3+). After ceasing the excitation, the long-lived trapped electrons can be thermally released to Mn^(2+) and Er^(3+) ions, resulting in both visible and NIR afterglow. Based on multi-modal emissions of the MYE-DP, we demonstrate a five-level anti-counterfeiting strategy, which significantly increases the anti-counterfeiting security. In addition, this work provides valuable insights into the energy transfer between STEs, Mn^(2+), Ln^(3+), and traps, laying a solid foundation for future development of new lead-free perovskites.

Tunable Multicolor Fluorescence of Perovskite-Based Composites for Optical Steganography and Light-Emitting Devices

Multicolor fluorescence of mixed halide perovskites enormously enables their applications in photonics and optoelectronics.However,it remains an arduous task to obtain multicolor emissions from perovskites containing single halogen to avoid phase segregation.Herein,a fluorescent composite containing Eu-based metal-organic frameworks(MOFs),OD Cs PbBre,and 3D CsPbBrs is synthesized.Under excitations at 365 nm and 254nm,the pristine composite emits blue(B)and red(R)fluorescence,which are ascribed to radiative defects within CsPbBr and 5Do→7F,transitions of Eu^(3+),respectively.Interestingly,after light soaking in the ambient environment,the blue fluorescence gradually converts into green(G)emission due to the defect repairing and 0D-3D phase conversion.This permanent and unique photochromic effect enables anticounterfeiting and microsteganography with increased security through a micropatterning technique.Moreover,the RGB luminescence is highly stable after encapsulation by a transparent polymer layer.Thus,trichromatic light-emitting modules are fabricated by using the fluorescent composites as color-converting layers,which almost fully cover the standard color gamut.Therefore,this work innovates a strategy for construction of tunable multicolor luminescence by manipulating the radiative defects and structural dimensionality.

Luminescence and recombine centre in ZnO/Si films

The D0h luminescence of ZnO films deposited on p-type Si substrates is produced by metal-organic chemical vapor deposition(MOCVD).After annealing in the air at 700°C for an hour,the photoluminescence(PL)spectra,the I-V characteristics and the deep level transient spectroscopy(DLTS)of the samples are measured.All the samples have a rectification characteristic.DLTS signals show two deep levels of E1 and E2.The Gaussian fit curves of the PL spectra at room temperature show three luminescence lines b,c and d,of which b is attributed to the exciton emission.The donor level E1 measured by DLTS and the location state donor ionization energy Ed of the closely neighboring emission lines c and d are correlated.E1 is judged as neutral donor bound to hole emission(D0h).Moreover,the intensity of the PL spectra decreases while the relative density of E2 increases,showing that E2 has the property of a nonradiative center.