Luminescence of undoped commercial ZnS crystals: A critical review and new evidence on the role of impurities using photoluminescence and electrical transient spectroscopy

Abstract

Bulk undoped ZnS materials exhibit relatively bright yet diverse luminescence behavior, which has, in recent years, been attributed to intrinsic defects. However, the luminescence also resembles that of doped materials, implying a role of impurities. Luminescence features have also been attributed to oxygen impurities causing defect clusters or energy band anti-crossing. Thus, this study couples optical and electrical techniques, such as band edge transmission, photoluminescence (PL), PL excitation, radioluminescence, thermoluminescence, optical deep level transient spectroscopy, and photoinduced current transient spectroscopy, to explore the identity of defect levels. ZnS materials studied are commercial single crystals made by physical vapor transport, high-pressure Bridgman, and powder processing. These undoped bulk ZnS exhibit luminescence behavior similar to that of reported doped ZnS powders (10−4 to 10−2 mol. % doping for luminescent materials). Dopants (such as Al, Cl, Cu, and Ag) are also commonly found impurities in ZnS; hence, it is reasonable to believe they have a role in the luminescence of nominally undoped ZnS. By comparing the variation in optical and electrical properties between samples to the processing method and the rich literature on intentionally doped ZnS, this study shows a possible dominant contribution of impurities and impurity-containing defects on the luminescence of bulk “undoped” ZnS. Hence, there is no need to resort to complex mechanisms to explain the luminescence, but rather the metal and halide impurities and their defect complexes determine the main characteristics of luminescence in this wide-bandgap semiconductor.

Alumina‐Protected, Durable and Photostable Zinc Sulfide Particles from Scalable Atomic Layer Deposition

“…The TRPL decays show two different lifetimes: a short lifetime (≈µs) and a long lifetime component (≈ms). For both radiative centers (SA and BCu; most likely originating from chloride and/or copper impurities of the industrially produced ZnS [24] ), lifetimes in the µs-regime have been reported, [47] in good agreement with the short lifetime component measured in this work. Due to electron traps that draw electrons from the after UV irradiation with a pulsed 355-nm nanosecond laser as a function of the illumination time (peak power density of the laser: 10.5 kW cm −2 ).…”

“…The uncoated ZnS shows a significant emission between 400 and 600 nm, most likely due to self-activated (SA) centers and/or Cu-interstitials (B-Cu) originating from trace amounts of chloride and/or copper, respectively, [23] which are common impurities in industrially produced undoped ZnS as reported in ref. [24]. For uncoated ZnS, the PL band decreases significantly with UV illumination time due to photocorrosion (R1-R4) of ZnS in the presence of water ( Figure 1a).…”

Femtosecond Double-Pulse Laser Ablation and Deposition of Co-Doped ZnS Thin Films

“…The PL spectrum of the Co:ZnS sample deposited on a Si substrate with 2 × 10 6 double pulse sequences and an interpulse delay of 10 ps ( Figure 5 c) shows a broad emission between 1.6 and 3.2 eV that can be deconvoluted into five Gaussian peaks centered at 2.84 eV (437 nm), 2.62 eV (473 nm), 2.35 eV (528 nm), 2.13 eV (582 nm), and 1.93 eV (642 nm), respectively. These emissions are related to native defects and/or impurities which introduce different levels in the band gap [ 68 ]. Precisely, the 2.84 eV peak is commonly attributed to sulfur vacancies acting as donor states [ 69 ], while the 2.62 eV band corresponds to the so-called self-activated emission of ZnS.…”

“…Although there is a general agreement that such luminescence is due to a DAP transition, the origin of the defects involved has not been clearly ascertained. Zinc vacancies, sulfur interstitials and Cu impurities are frequently proposed as the acceptor levels, while possible donors include sulfur vacancies, Al, or Cl impurities [ 68 , 72 , 73 , 74 ]. The intensity of the green PL has been found to increase in Co-doped ZnS thin films with the dopant concentration, which is attributed to the role played by Co 2+ ions as sensitizing agents enhancing the corresponding radiative recombination process [ 21 ].…”

Оптические свойства нанопорошков сульфида цинка и гетеронаноструктур ZnS/Ag-=SUB=-2-=/SUB=-S

“…Измерения люминесцентных свойств нанопорошков ZnS с близким размером частиц 2, 2.5 и 4 nm в диапазоне от 410 до 820 nm при возбуждении излучением с длиной волны λ = 330 nm (рис. 8) показали, что наноструктурированный сульфид цинка имеет спектр люминесценции с максимумом интенсивности около 430 nm, типичный для крупнокристаллического сульфида цинка [33]. Наблюдаемые спектры связаны с рекомбинацией носителей заряда с участием собственных и примесных дефектов, происходящей по донорно-акцепторному механизму.…”