Temp-Dependent PL in Perovskite QDs

• Temperature-dependent photoluminescence in perovskite QDs is a phenomenon where optical emissions shift with temperature due to quantum confinement, electron–phonon interactions, and phase transitions.
• It reveals critical insights into bandgap tuning, excitonic fine structure, and the balance between radiative and nonradiative processes essential for optoelectronic and quantum device optimization.
• Experimental and theoretical studies combine temperature-resolved spectroscopy with advanced modeling to elucidate carrier dynamics, trap activation, and strategies for enhancing thermal stability.

Temperature-dependent photoluminescence (PL) in perovskite quantum dots (QDs) serves as a crucial probe of quantum confinement, exciton-phonon coupling, quantum efficiency, and structural dynamics as a function of thermal environment. This phenomenon underlies fundamental materials science, device engineering, and emerging quantum technologies based on perovskite nanomaterials. The interplay between temperature, composition, surface passivation, quantum confinement, and local environment yields complex and highly tunable PL signatures that encode information on structural phase, carrier dynamics, and optoelectronic functionality.

1. Fundamental Physical Principles of Temperature-Dependent Photoluminescence in Perovskite QDs

The temperature dependence of PL in halide perovskite QDs arises from competition and interplay between lattice thermal expansion, electron–phonon interactions, ion migration, quantum confinement, and surface or defect-mediated recombination channels. Upon increasing temperature, several distinct and sometimes counteracting effects are observed:

• Bandgap Shifts: Depending on halide composition and phase, the PL peak energy may blue-shift or red-shift with temperature. In CsPbBr₃ QDs, a linear blue-shift with T (0.25 meV/K for T < 220 K) is observed owing to dominant thermal expansion; at higher T, electron–phonon coupling counterbalances expansion, leading to temperature-independent chromaticity (Wei et al., 2016). By contrast, CsPbCl₃-rich QDs display a sign reversal (negative temperature coefficient), controlled by an anomalous electron–phonon coupling involving Cs rattling and octahedral tilting, overtaking the thermal expansion contribution at Cl > 40% and driving the bandgap to decrease with T (Fasahat et al., 20 Nov 2024). The total temperature derivative of the gap is

$$\frac{dE_g}{dT} = \left.\frac{\partial E_g}{\partial T}\right|_\text{TE} + \sum_i \left.\frac{\partial E_g}{\partial T}\right|_{\text{EP},i}$$

where the TE (thermal expansion) term is typically positive and the anomalous EP (electron–phonon) contribution can be negative.

• Excitonic Fine Structure and Confined States: At cryogenic temperatures, individual CsPbBr₃ QDs display well-resolved band-edge multiplets from bright-triplet excitons, with size-dependent energy splittings ($\Delta \sim 1.3\ \mathrm{meV}$), fully attributable to quantum confinement effects enhancing electron–hole exchange (Amara et al., 2023). Boltzmann population statistics direct the intensity distribution among these split states, so even modest changes in T (e.g., from 10 K to 16 K) alter the relative PL peak strengths. Trion and biexciton binding energies, scaling as $E_\mathrm{shift} = A + B/L^2$, are similarly sharpened and tunable.
• PL Linewidth and Broadening: As T increases, the PL spectrum typically broadens. The FWHM is effectively modeled as

$$\Gamma(T) = \Gamma_\mathrm{inh} + \frac{\gamma_\mathrm{ph}}{\exp(E_a/k_B T) - 1}$$

with the activation energy $E_a$ linked to quantum confinement or LO phonon energies (Kulebyakina et al., 2023, Kozlov et al., 2018). The dominant broadening processes transition from inhomogeneous (static) at low T to dynamic (phonon-coupled, carrier activation, surface trapping) at higher T.

• Carrier Trapping and Nonradiative Channels: At low T, radiative recombination is the prevailing process, but as T increases, nonradiative channels—including carrier activation to trap states, structural transformations, and increased surface interactions—result in PL quenching and faster decay (Kulebyakina et al., 2023, Kozlov et al., 2018). For ensembles with high defect or trap densities, a population of QDs transitions from "emissive" at low T to "nonemissive" at higher T due to ultrafast trapping.
• Phase Transitions: The orthorhombic–tetragonal–cubic transitions in perovskites (e.g., MAPbI₃, MAPbBr₃) lead to abrupt changes in both PL energy and lineshape. Intensity ratios of multiple emission peaks track the fraction of material in different phases, and carrier transfer between domains modulates the observed PL (Campanari et al., 2020, Niesner et al., 2016).

2. Experimental Signatures and Modeling of Temperature-Dependent PL

Several experimental platforms and analyses elucidate the nuances of temperature dependence:

• Temperature-Resolved Steady-State and Time-Resolved PL Spectroscopy: Routine mapping from cryogenic (6 K) to near-ambient (>300 K) reveals nonmonotonic intensity, peak position, and linewidth variations (Kulebyakina et al., 2023, Wei et al., 2016, Kozlov et al., 2018). In glass-matrix CsPbBr₃ or CsPb(Cl,Br)₃ QDs, multiexponential PL decay with temperature-evolving components ($\sim$1 ns, 10 ns, 1 μs) traces the balance between direct radiative recombination, trap relaxation, and thermal activation (Kulebyakina et al., 2023).

Temperature Regime	Dominant PL Mechanism	Characteristic Behavior
<40 K	Direct radiative/exciton fine structure	Sharp peaks, slow nonradiative decay
40–140 K	Trap-assisted, phonon-limited	Onset of linewidth broadening, emergent trap processes
>140 K	Thermally-activated recombination	Intensity quenching, short-lived, nonradiative dominated

• Fine Structure and Polarization: Polarization-resolved experiments correlate spectral structure to the orientation of multiple, orthogonal excitonic dipoles, enabling the simulation of observed PL variations as a function of $T$ and QD orientation (Amara et al., 2023).
• Fitting Models: Rate equations capturing the interplay between exciton ground, trap, and excited states, augmented by thermally-activated rate constants and phonon occupation factors (Bose–Einstein), quantitatively reproduce the multi-component decay and intensity quenching in CsPbBr₃ and CsPb(Cl,Br)₃ QDs (Kulebyakina et al., 2023, Kozlov et al., 2018). For carrier trapping regimes, a model in which "switching off" of NCs depends on a Poisson distribution of surface traps successfully accounts for the observed temperature quenching (Kulebyakina et al., 2023). In CdTe or CdSe/ZnS QDs, similar approaches but with different physical interpretations have been developed (Murphy et al., 2016, Lan et al., 2015).

3. Influence of Composition, Quantum Confinement, and Surface Passivation

• Halide Composition & Structure: The sign and slope of the PL peak shift with temperature is governed by the halide content and associated phase. In CsPb(Br₁₋ₓClₓ)₃ NCs, moving beyond 40% Cl fundamentally changes the electron–phonon coupling mechanism and thus the temperature dependence of the band gap (Fasahat et al., 20 Nov 2024).
• Quantum Confinement: PL fine structure—both the observed energy splittings and the presence of phonon replicas—exhibits a characteristic dependence on QD size, with stronger confinement (smaller NCs) inducing higher splittings and enhanced exciton–phonon coupling (indexed by increased Huang–Rhys factors) (Amara et al., 2023). Nevertheless, the phonon energies themselves remain nearly constant, supporting their assignment to bulk rather than surface modes.
• Surface Chemistry: Surface passivation is a principal determinant of nonradiative recombination rates at elevated temperatures (Ijaz et al., 2020). Nanocrystals passivated with quaternary ammonium bromide (QAB) ligands exhibit more robust, monoexponential PL decay over a wide T range and higher PL intensities, as thermal energy competes less readily with strong ligand binding. Residual PL quenching at high T suggests that new, even more robust passivation schemes are needed for device applications.
• Trap State Formation and Distribution: QD ensembles embedded in glass or as films display temperature-induced transitions from emissive to nonemissive states, governed by structural dynamics at surfaces or interiors and not simply by a gradual rise in nonradiative rates (Kozlov et al., 2018). The nonemissive fraction can grow from ~40% at 20 K to >90% at 300 K. High-concentration or poorly passivated monolayers show stronger PL quenching due to increased trap density (Murphy et al., 2016).

4. Theoretical Formulation: Planck Law, Chemical Potential, and Phonon Effects

• Generalized Planck Law: A quantum-statistical view of PL, incorporating the temperature- and carrier-density-dependent chemical potential $\mu$, is essential for describing emission under non-equilibrium conditions. When $\mu>0$, nonthermal PL dominates; at a critical temperature $T_c$ where $\mu\to0$, PL transitions to thermal emission (Kurtulik et al., 2020). The generalized Planck law is

$$L(\nu,T) = \epsilon \frac{2\nu^2}{c^3}\frac{(h\nu-\mu)}{\exp{\left( (h\nu-\mu)/(k_BT) \right)}-1}$$

In perovskite QDs, this paradigm rationalizes observed blue-shifts and emission conservation below $T_c$, as well as the eventual transition to thermally driven emission at high T.

• Phonon-Induced Quenching and Universal Points: Phonon interactions, particularly in a three-level system, give rise to temperature-dependent nonradiative processes and photon rate “quenching” below $T_c$. The emissivity is constrained by the external quantum efficiency (EQE), yielding a universal crossing point in the emission rate-versus-temperature curves (Kurtulik et al., 2020).
• Mathematical Frameworks for Trap Activation: The activation of nonradiative processes and spectral broadening are describable via Arrhenius-type activated rates and mutually coupled differential rates for trap occupation and release, for both shallow and deep traps.

5. Phase Segregation, Ion Migration, and Dynamic Disorder

• Mixed-Halide Perovskites: In MAPbBr₂.₅I₀.₅ and analogs, illumination-induced phase segregation is directly tracked in the temperature evolution of PL. Upon photoexcitation, iodine rapidly segregates into domains (lowering the bandgap), yielding transient intermediate PL peaks—a process strongly retarded at low T and accelerated at elevated T (Verkhogliadov et al., 2023). The evolution of PL lifetimes (extracted via bi-exponential fits) and intensity traces the kinetics of migration and phase transition (orthorhombic–tetragonal, 110–180 K), which both modulate the funneling of carriers and stability against photodamage or trapping.
• Defects and Phase Transitions: In MAPbI₃, the interplay of phase coexistence and defect bands at low T gives rise to a complex structure of PL peaks, with carrier transfer, state filling, and defect band saturation leading to nontrivial dependences of intensity ratios and blue/red-shifts as T and excitation density are varied (Campanari et al., 2020). The onset of amplified spontaneous emission under high excitation at low T aligns with the suppression of defect-related recombination and mirrors the behavior in direct-gap inorganic semiconductors.

6. Environmental Engineering and Cavity Integration

• Nanoantenna and Cavity Coupling: Lithographically defined nanoantenna arrays (e.g., q-BIC structures (Csányi et al., 2023)) and plasmonic ring microcavities (Li et al., 11 Aug 2025) offer non-invasive means to tune and enhance perovskite QD PL via Purcell effect and electromagnetic mode engineering. For CsPbBr₃ QDs in plasmonic cavities, deterministic integration realizes a four-fold PL intensity enhancement and up to threefold lifetime reduction at room temperature, with a twofold reduction recorded at 4 K for single QDs (Li et al., 11 Aug 2025). Polarization control and localized field engineering can further modulate both the emission wavelength (tunable over ~39 nm range) and the directionality of emission, stabilizing against some thermal broadening and intensity losses even under varying environmental conditions.

Method	PL Shift/Tuning Range	Intensity Enhancement	Lifetime Reduction	Temperature Regime
Plasmonic ring cavity	-	4× (ensembles)	3× at RT, 2× at 4 K	4 K–300 K (Li et al., 11 Aug 2025)
q-BIC nanoantenna array	~39 nm	up to 21×	-	Ambient (Csányi et al., 2023)

• Stability Considerations: Because q-BIC and plasmonic approaches manipulate optical modes rather than the QD chemical structure, performance is robust to moderate temperature variations, with field enhancement and spectral tuning "overriding" many thermal quenching effects characteristic of conventional approaches.

7. Implications for Device Applications and Research Outlook

The intricate temperature dependence of PL in perovskite QDs, governed by the interplay of structural, compositional, and environmental factors, has profound implications for optoelectronic device design:

• Light Emission Technologies: Temperature-stable chromaticity, maximized via careful control of lattice expansion and electron–phonon coupling, directly improves color-stable light-emitting diodes and lasers (Wei et al., 2016, Csányi et al., 2023).
• Quantum Information Processing: Enhanced, directional, and fast-decay single-photon emission through cavity integration supports the realization of perovskite-based quantum photonic circuits (Li et al., 11 Aug 2025).
• Thermal Sensing and Memory: The irreversible PL shift upon heating in certain QDs enables thermal history nanosensors for environments where real-time temperature logging is infeasible (Lan et al., 2015).
• Material Engineering: Understanding the role of dynamic disorder (e.g., Cs rattlers, octahedral tiltings) and optimizing passivation, crystal phase, and compositional tuning (Br/Cl/I ratio) is key for further enhancing quantum efficiency and operational stability under varying temperatures (Fasahat et al., 20 Nov 2024, Ijaz et al., 2020, Verkhogliadov et al., 2023).

A growing body of work elucidates the theoretical underpinnings (generalized Planck/chemical potential formalism (Kurtulik et al., 2020)), advances deterministic integration strategies (Li et al., 11 Aug 2025), and exploits environmental engineering of radiative channels (Csányi et al., 2023), which together position perovskite QDs as versatile, highly tunable materials at the forefront of next-generation quantum and optoelectronic technologies.