My extended abstract for more depth!

Introduction

Halide perovskites are a family of materials making big waves in the science world for next-generation technology, including medical biosensing, light-emitting diodes (LEDs), and solar cells. Usually, these materials are lead-based. However, traditional lead-based perovskites face two major roadblocks: lead is super toxic, and the materials tend to degrade quickly when exposed to normal air and moisture.

To solve this, scientists are working to develop lead-free alternatives that are both environmentally friendly and stable. One method to supercharge these new materials is a process called "doping". Which is introducing tiny amounts of rare-earth elements, like Erbium (Er³⁺). These rare-earth elements act like internal light bulbs, producing incredibly sharp, predictable colors of light when energized.

This study investigates how Erbium doping changes the optical behavior of two lead-free materials: CAIC (Cs₂AgInCl₆) and CMBC (Cs₄MnBi₂Cl₁₂). To see how well they fluoresce, we compared them to a classic lead-based benchmark material: KPC (KPb₂Cl₅).

Goals and Methods:

The primary goals of this study were:

1. Synthesize the Erbium-doped lead-free materials using a high pressure, hydrothermal method.
2. Characterize exactly how these materials absorb and emit light using a spectrofluorometer.
3. Compare our lead-free creations to the lead-based benchmark (KPC).

Hydrothermal Synthesis

To create these crystals, we used a hydrothermal method, which acts like an ultra-high-temperature pressure cooker to force high-quality crystal growth. This method involved:

• Carefully weighing out precise precursor chemicals.
• Placing the mixture into a tightly sealed, acid-resistant teflon vessel with 10 mL of hydrochloric acid (HCl).
• Locking the vessel inside a stainless steel jacket and heating it in a furnace at 180°C (356°F) for 48 hours.
• Safely cooling the mixture to room temperature, washing the brand-new crystal powders with ethanol, and drying them.

Characterization Techniques

To analyze how our new crystals handle light, we placed them into a spectrofluorometer to perform:

• Emission scans - Shining a fixed laser (like a UV or blue laser) at the sample to see what color it glows.
• Excitation scans - Shifting through different wavelengths of light to find out exactly which energy level triggers the absolute brightest glow.

Results

Visible Fluorescence

Both Er: CMBC and Er: KPC exhibited strong visible fluorescence under UV light, whereas Er: CAIC did not show significant emission. This suggests that the host material plays a critical role in the optical activity of Er³⁺ ions.

Excitation and Emission Spectroscopy

• Er: KPC showed incredibly sharp, easily-identifiable peaks that align with the characteristics of Er³⁺ transitions.
• Er: CMBC, however, presented broad energy bands. This tells us that the Manganese (Mn²⁺) is absorbing broad spectrum light and efficiently passing that energy off to our Erbium ions.

Sample Calculation: Er³⁺ Transition Energy

To verify the origin of the observed emission peaks, transition energies were calculated using the known electronic energy levels of Er³⁺ from a Dieke diagram.

Using the equation λ = 10⁷ / ΔE allows for the wavelengths emitted/absorbed by different electron transitions. For example:

For the transition ⁴I_15/2 → ⁴S_3/2:

ΔE = E_final - E_initial → 18500cm^-1 - 0

So... ΔE = 18500cm^-1

λ = 10⁷ / 18500cm^-1 = 540.5 nm

Conclusions

1. Success without Lead: The high-pressure hydrothermal method effectively cooks up brilliant, optically active crystals without needing toxic lead ingredients.
2. The Host with the Most... Fluorescence: The choice of host material plays a huge role in the final performance. Multiple different colors can be achieved (or the light can be snuffed entirely) by swapping the structural host lattice.
3. Direct vs. Hand-off Energy: Er:KPC displays direct excitation paths, whereas Er:CMBC relies on broad Mn²⁺ interactions to absorb light and pass it off to the Er³⁺.
4. Customizable Tech: Because we can alter emission pathways and colors effortlessly, lead-free perovskites prove to be highly tunable and useful for future green tech, biophotonics, and future commercial lighting.